TL;DR: This doesn't appear to be ext4 specific, and seems to involve an unholy combination of the perf_event_open(2) and sendfile(2) system calls. On Mon, Feb 25, 2019 at 10:50:05PM -0800, syzbot wrote: > syzbot found the following crash on: > > HEAD commit: 8a61716ff2ab Merge tag 'ceph-for-5.0-rc8' of git://github... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=161b71d4c00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=7132344728e7ec3f > dashboard link: https://syzkaller.appspot.com/bug?extid=7d19c5fe6a3f1161abb7 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=103908f8c00000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=105e5cd0c00000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+7d19c5fe6a3f1161abb7@xxxxxxxxxxxxxxxxxxxxxxxxx > > audit: type=1400 audit(1550814986.750:36): avc: denied { map } for > pid=8058 comm="syz-executor004" path="/root/syz-executor004991115" > dev="sda1" ino=1426 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 > tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1 > hrtimer: interrupt took 42841 ns > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: > rcu: (detected by 1, t=10502 jiffies, g=5873, q=2) > rcu: All QSes seen, last rcu_preempt kthread activity 10502 > (4295059997-4295049495), jiffies_till_next_fqs=1, root ->qsmask 0x0 > syz-executor004 R running task 26448 8069 8060 0x00000000 This particular repro seems to induce similar failures when I tried it with xfs and btrfs as well as ext4. The repro seems to involve the perf_event_open(2) and sendfile(2) system calls, and killing the process which is performing the sendfile(2). The repro also uses the sched_setattr(2) system call, but when I commented it out, the failure still happened, so this appears to be another case of "Syzkaller? We don't need to bug developers with a minimal test case! Open source developers are a free unlimited resource, after all!" :-) Commenting out the perf_event_open(2) does seem to make the problem go away. Since there are zillions of ways to self-DOS a Linux server without having to resert to exotic combination of system calls, this isn't something I'm going to prioritize for myself, but I'm hoping someone else has time and curiosity. - Ted
// autogenerated by syzkaller (https://github.com/google/syzkaller) #define _GNU_SOURCE #include <dirent.h> #include <endian.h> #include <errno.h> #include <fcntl.h> #include <pthread.h> #include <signal.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/ioctl.h> #include <sys/mount.h> #include <sys/prctl.h> #include <sys/stat.h> #include <sys/syscall.h> #include <sys/types.h> #include <sys/wait.h> #include <time.h> #include <unistd.h> #include <linux/futex.h> unsigned long long procid; static void sleep_ms(uint64_t ms) { usleep(ms * 1000); } static uint64_t current_time_ms(void) { struct timespec ts; if (clock_gettime(CLOCK_MONOTONIC, &ts)) exit(1); return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000; } static void use_temporary_dir(void) { char tmpdir_template[] = "./syzkaller.XXXXXX"; char* tmpdir = mkdtemp(tmpdir_template); if (!tmpdir) exit(1); if (chmod(tmpdir, 0777)) exit(1); if (chdir(tmpdir)) exit(1); } static void thread_start(void* (*fn)(void*), void* arg) { pthread_t th; pthread_attr_t attr; pthread_attr_init(&attr); pthread_attr_setstacksize(&attr, 128 << 10); int i; for (i = 0; i < 100; i++) { if (pthread_create(&th, &attr, fn, arg) == 0) { pthread_attr_destroy(&attr); return; } if (errno == EAGAIN) { usleep(50); continue; } break; } exit(1); } #define BITMASK(bf_off, bf_len) (((1ull << (bf_len)) - 1) << (bf_off)) #define STORE_BY_BITMASK(type, htobe, addr, val, bf_off, bf_len) \ *(type*)(addr) = \ htobe((htobe(*(type*)(addr)) & ~BITMASK((bf_off), (bf_len))) | \ (((type)(val) << (bf_off)) & BITMASK((bf_off), (bf_len)))) typedef struct { int state; } event_t; static void event_init(event_t* ev) { ev->state = 0; } static void event_reset(event_t* ev) { ev->state = 0; } static void event_set(event_t* ev) { if (ev->state) exit(1); __atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE); syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG); } static void event_wait(event_t* ev) { while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0); } static int event_isset(event_t* ev) { return __atomic_load_n(&ev->state, __ATOMIC_ACQUIRE); } static int event_timedwait(event_t* ev, uint64_t timeout) { uint64_t start = current_time_ms(); uint64_t now = start; for (;;) { uint64_t remain = timeout - (now - start); struct timespec ts; ts.tv_sec = remain / 1000; ts.tv_nsec = (remain % 1000) * 1000 * 1000; syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, &ts); if (__atomic_load_n(&ev->state, __ATOMIC_RELAXED)) return 1; now = current_time_ms(); if (now - start > timeout) return 0; } } #define FS_IOC_SETFLAGS _IOW('f', 2, long) static void remove_dir(const char* dir) { DIR* dp; struct dirent* ep; int iter = 0; retry: while (umount2(dir, MNT_DETACH) == 0) { } dp = opendir(dir); if (dp == NULL) { if (errno == EMFILE) { exit(1); } exit(1); } while ((ep = readdir(dp))) { if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0) continue; char filename[FILENAME_MAX]; snprintf(filename, sizeof(filename), "%s/%s", dir, ep->d_name); while (umount2(filename, MNT_DETACH) == 0) { } struct stat st; if (lstat(filename, &st)) exit(1); if (S_ISDIR(st.st_mode)) { remove_dir(filename); continue; } int i; for (i = 0;; i++) { if (unlink(filename) == 0) break; if (errno == EPERM) { int fd = open(filename, O_RDONLY); if (fd != -1) { long flags = 0; if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0) close(fd); continue; } } if (errno == EROFS) { break; } if (errno != EBUSY || i > 100) exit(1); if (umount2(filename, MNT_DETACH)) exit(1); } } closedir(dp); int i; for (i = 0;; i++) { if (rmdir(dir) == 0) break; if (i < 100) { if (errno == EPERM) { int fd = open(dir, O_RDONLY); if (fd != -1) { long flags = 0; if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0) close(fd); continue; } } if (errno == EROFS) { break; } if (errno == EBUSY) { if (umount2(dir, MNT_DETACH)) exit(1); continue; } if (errno == ENOTEMPTY) { if (iter < 100) { iter++; goto retry; } } } exit(1); } } static void kill_and_wait(int pid, int* status) { kill(-pid, SIGKILL); kill(pid, SIGKILL); int i; for (i = 0; i < 100; i++) { if (waitpid(-1, status, WNOHANG | __WALL) == pid) return; usleep(1000); } DIR* dir = opendir("/sys/fs/fuse/connections"); if (dir) { for (;;) { struct dirent* ent = readdir(dir); if (!ent) break; if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0) continue; char abort[300]; snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort", ent->d_name); int fd = open(abort, O_WRONLY); if (fd == -1) { continue; } if (write(fd, abort, 1) < 0) { } close(fd); } closedir(dir); } else { } while (waitpid(-1, status, __WALL) != pid) { } } #define SYZ_HAVE_SETUP_TEST 1 static void setup_test() { prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0); setpgrp(); } #define SYZ_HAVE_RESET_TEST 1 static void reset_test() { int fd; for (fd = 3; fd < 30; fd++) close(fd); } struct thread_t { int created, call; event_t ready, done; }; static struct thread_t threads[16]; static void execute_call(int call); static int running; static void* thr(void* arg) { struct thread_t* th = (struct thread_t*)arg; for (;;) { event_wait(&th->ready); event_reset(&th->ready); execute_call(th->call); __atomic_fetch_sub(&running, 1, __ATOMIC_RELAXED); event_set(&th->done); } return 0; } static void execute_one(void) { int i, call, thread; int collide = 0; again: for (call = 0; call < 5; call++) { for (thread = 0; thread < (int)(sizeof(threads) / sizeof(threads[0])); thread++) { struct thread_t* th = &threads[thread]; if (!th->created) { th->created = 1; event_init(&th->ready); event_init(&th->done); event_set(&th->done); thread_start(thr, th); } if (!event_isset(&th->done)) continue; event_reset(&th->done); th->call = call; __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED); event_set(&th->ready); if (collide && (call % 2) == 0) break; event_timedwait(&th->done, 45); break; } } for (i = 0; i < 100 && __atomic_load_n(&running, __ATOMIC_RELAXED); i++) sleep_ms(1); if (!collide) { collide = 1; goto again; } } static void execute_one(void); #define WAIT_FLAGS __WALL static void loop(void) { int iter; for (iter = 0;; iter++) { char cwdbuf[32]; sprintf(cwdbuf, "./%d", iter); if (mkdir(cwdbuf, 0777)) exit(1); int pid = fork(); if (pid < 0) exit(1); if (pid == 0) { if (chdir(cwdbuf)) exit(1); setup_test(); execute_one(); reset_test(); exit(0); } int status = 0; uint64_t start = current_time_ms(); for (;;) { if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid) break; sleep_ms(1); if (current_time_ms() - start < 5 * 1000) continue; kill_and_wait(pid, &status); break; } remove_dir(cwdbuf); } } #ifndef __NR_sched_setattr #define __NR_sched_setattr 314 #endif uint64_t r[1] = {0xffffffffffffffff}; void execute_call(int call) { long res; switch (call) { case 0: memcpy((void*)0x20000040, "./bus\000", 6); res = syscall(__NR_open, 0x20000040, 0x1fe, 0); if (res != -1) r[0] = res; break; case 1: memcpy((void*)0x200001c0, "\x15\x8a\xdd\x00", 4); syscall(__NR_write, r[0], 0x200001c0, 4); break; case 2: *(uint32_t*)0x20000800 = 1; *(uint32_t*)0x20000804 = 0x70; *(uint8_t*)0x20000808 = 0; *(uint8_t*)0x20000809 = 0; *(uint8_t*)0x2000080a = 0; *(uint8_t*)0x2000080b = 0; *(uint32_t*)0x2000080c = 0; *(uint64_t*)0x20000810 = 0x50a; *(uint64_t*)0x20000818 = 0; *(uint64_t*)0x20000820 = 0; STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 0, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 1, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 2, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 3, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 4, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 7, 5, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 6, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 7, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 8, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 9, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 10, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 11, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 12, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 13, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0x7fff, 14, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 15, 2); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 17, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 18, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 19, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 20, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 21, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 22, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 23, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 24, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 25, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 26, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 27, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 28, 1); STORE_BY_BITMASK(uint64_t, , 0x20000828, 0, 29, 35); *(uint32_t*)0x20000830 = 0; *(uint32_t*)0x20000834 = 0; *(uint64_t*)0x20000838 = 0; *(uint64_t*)0x20000840 = 0; *(uint64_t*)0x20000848 = 0; *(uint64_t*)0x20000850 = 0; *(uint32_t*)0x20000858 = 0; *(uint32_t*)0x2000085c = 0; *(uint64_t*)0x20000860 = 0; *(uint32_t*)0x20000868 = 0xfffffffd; *(uint16_t*)0x2000086c = 0; *(uint16_t*)0x2000086e = 0; syscall(__NR_perf_event_open, 0x20000800, 0, -1, -1, 0); break; case 3: *(uint64_t*)0x20000000 = 0; syscall(__NR_sendfile, r[0], r[0], 0x20000000, 0x8080fffffffe); break; #if 0 case 4: *(uint32_t*)0x200002c0 = 0; *(uint32_t*)0x200002c4 = 2; *(uint64_t*)0x200002c8 = 0; *(uint32_t*)0x200002d0 = 0; *(uint32_t*)0x200002d4 = 3; *(uint64_t*)0x200002d8 = 0; *(uint64_t*)0x200002e0 = 0; *(uint64_t*)0x200002e8 = 0; syscall(__NR_sched_setattr, 0, 0x200002c0, 0); break; #endif } } int main(void) { syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0); for (procid = 0; procid < 6; procid++) { if (fork() == 0) { use_temporary_dir(); loop(); } } sleep(1000000); return 0; }
