Re: [syzbot] [bpf?] KMSAN: uninit-value in bstr_printf

xingwei lee
2024-02-23T15:44:18Z

Hello, I reproduced this bug in the upstream linux.

If you fix this issue, please add the following tag to the commit:
Reported-by: xingwei lee <xrivendell7@gmail.com>

Notice: I use the same config with syzbot dashboard.
kernel version: c1ca10ceffbb289ed02feaf005bc9ee6095b4507
kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e3dd779fba027968
with KASAN enabled
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

=====================================================
BUG: KMSAN: uninit-value in bstr_printf+0x1c57/0x1e30 lib/vsprintf.c:3334
bstr_printf+0x1c57/0x1e30 lib/vsprintf.c:3334
____bpf_snprintf kernel/bpf/helpers.c:1064 [inline]
bpf_snprintf+0x1eb/0x3c0 kernel/bpf/helpers.c:1044
___bpf_prog_run+0x232b/0xe6a0 kernel/bpf/core.c:1986
__bpf_prog_run288+0xc0/0xf0 kernel/bpf/core.c:2226
bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
__bpf_prog_run include/linux/filter.h:651 [inline]
bpf_prog_run include/linux/filter.h:658 [inline]
bpf_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
bpf_flow_dissect+0x13c/0x490 net/core/flow_dissector.c:991
bpf_prog_test_run_flow_dissector+0x78c/0xad0 net/bpf/test_run.c:1359
bpf_prog_test_run+0x74c/0xb90 kernel/bpf/syscall.c:4107
__sys_bpf+0x73b/0xfe0 kernel/bpf/syscall.c:5475
__do_sys_bpf kernel/bpf/syscall.c:5561 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5559 [inline]
__x64_sys_bpf+0xa9/0xf0 kernel/bpf/syscall.c:5559
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

=* repro.c =*
// 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 <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.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>

#ifndef __NR_bpf
#define __NR_bpf 321
#endif

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 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 = 0;
for (; 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);
}

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, 1000000);
}

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_ACQUIRE))
return 1;
now = current_time_ms();
if (now - start > timeout)
return 0;
}
}

static bool write_file(const char* file, const char* what, ...) {
char buf[1024];
va_list args;
va_start(args, what);
vsnprintf(buf, sizeof(buf), what, args);
va_end(args);
buf[sizeof(buf) - 1] = 0;
int len = strlen(buf);
int fd = open(file, O_WRONLY | O_CLOEXEC);
if (fd == -1)
return false;
if (write(fd, buf, len) != len) {
int err = errno;
close(fd);
errno = err;
return false;
}
close(fd);
return true;
}

static void kill_and_wait(int pid, int* status) {
kill(-pid, SIGKILL);
kill(pid, SIGKILL);
for (int 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) {
}
}

static void setup_test() {
prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
setpgrp();
write_file("/proc/self/oom_score_adj", "1000");
}

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;
for (call = 0; call < 6; 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);
event_timedwait(&th->done, 50);
break;
}
}
for (i = 0; i < 100 && __atomic_load_n(&running, __ATOMIC_RELAXED); i++)
sleep_ms(1);
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void) {
int iter = 0;
for (;; iter++) {
int pid = fork();
if (pid < 0)
exit(1);
if (pid == 0) {
setup_test();
execute_one();
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 < 5000)
continue;
kill_and_wait(pid, &status);
break;
}
}
}

uint64_t r[4] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff,
0xffffffffffffffff};

void execute_call(int call) {
intptr_t res = 0;
switch (call) {
case 0:
*(uint32_t*)0x20000340 = 2;
*(uint32_t*)0x20000344 = 4;
*(uint32_t*)0x20000348 = 8;
*(uint32_t*)0x2000034c = 1;
*(uint32_t*)0x20000350 = 0x80;
*(uint32_t*)0x20000354 = 0;
*(uint32_t*)0x20000358 = 0;
memset((void*)0x2000035c, 0, 16);
*(uint32_t*)0x2000036c = 0;
*(uint32_t*)0x20000370 = -1;
*(uint32_t*)0x20000374 = 0;
*(uint32_t*)0x20000378 = 0;
*(uint32_t*)0x2000037c = 0;
*(uint64_t*)0x20000380 = 0;
res =
syscall(__NR_bpf, /*cmd=*/0ul, /*arg=*/0x20000340ul, /*size=*/0x48ul);
if (res != -1)
r[0] = res;
break;
case 1:
*(uint32_t*)0x20000180 = r[0];
*(uint64_t*)0x20000188 = 0x20000100;
*(uint32_t*)0x20000100 = 0;
*(uint64_t*)0x20000190 = 0x20000140;
memcpy((void*)0x20000140, "%pi6 \000", 8);
*(uint64_t*)0x20000198 = 0;
res =
syscall(__NR_bpf, /*cmd=*/2ul, /*arg=*/0x20000180ul, /*size=*/0x20ul);
if (res != -1)
r[1] = *(uint32_t*)0x20000180;
break;
case 2:
*(uint32_t*)0x20000440 = r[1];
*(uint64_t*)0x20000448 = 0x200002c0;
*(uint32_t*)0x200002c0 = 0;
*(uint64_t*)0x20000450 = 0x20000400;
memcpy((void*)0x20000400, "%pS \000", 8);
*(uint64_t*)0x20000458 = 0;
syscall(__NR_bpf, /*cmd=*/2ul, /*arg=*/0x20000440ul, /*size=*/0x20ul);
break;
case 3:
*(uint32_t*)0x200000c0 = r[1];
res =
syscall(__NR_bpf, /*cmd=*/0x16ul, /*arg=*/0x200000c0ul, /*size=*/4ul);
if (res != -1)
r[2] = *(uint32_t*)0x200000c0;
break;
case 4:
*(uint32_t*)0x200004c0 = 0x16;
*(uint32_t*)0x200004c4 = 0x10;
*(uint64_t*)0x200004c8 = 0x20000040;
memcpy((void*)0x20000040,
"\x18\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\xb7\x08\x00\x00\x00\x00\x00\x00\x7b\x8a\xf8\xff\x00\x00\x00\x00"
"\xb7\x08\x00\x00\xff\xff\x0b\x86\x7b\x8a\xf0\xff\x00\x00\x00\x00"
"\xbf\xa1\x00\x00\x00\x00\x00\x00\x07\x01\x00\x00\xf8\xff\xff\xff"
"\xbf\xa4\x00\x00\x00\x00\x00\x00\x07\x04\x00\x00\xf0\xfe\xff\xff"
"\xb7\x02\x00\x00\x08\x00\x00\x00\x18\x23\x00\x00",
92);
*(uint32_t*)0x2000009c = r[2];
memcpy((void*)0x200000a0,
"\x00\x00\x00\x00\x00\x00\x00\x00\xb7\x05\x00\x00\x08\x00\x00\x00"
"\x85\x00\x00\x00\xa5\x00\x00\x00\x95",
25);
*(uint64_t*)0x200004d0 = 0x20000600;
memcpy((void*)0x20000600, "GPL\000", 4);
*(uint32_t*)0x200004d8 = 0;
*(uint32_t*)0x200004dc = 0;
*(uint64_t*)0x200004e0 = 0;
*(uint32_t*)0x200004e8 = 0;
*(uint32_t*)0x200004ec = 0;
memset((void*)0x200004f0, 0, 16);
*(uint32_t*)0x20000500 = 0;
*(uint32_t*)0x20000504 = 0;
*(uint32_t*)0x20000508 = 0;
*(uint32_t*)0x2000050c = 0;
*(uint64_t*)0x20000510 = 0;
*(uint32_t*)0x20000518 = 0;
*(uint32_t*)0x2000051c = 0;
*(uint64_t*)0x20000520 = 0;
*(uint32_t*)0x20000528 = 0;
*(uint32_t*)0x2000052c = 0;
*(uint32_t*)0x20000530 = 0;
*(uint32_t*)0x20000534 = 0;
*(uint64_t*)0x20000538 = 0;
*(uint64_t*)0x20000540 = 0;
*(uint32_t*)0x20000548 = 0;
*(uint32_t*)0x2000054c = 0;
res =
syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x200004c0ul, /*size=*/0x90ul);
if (res != -1)
r[3] = res;
break;
case 5:
*(uint32_t*)0x20000640 = r[3];
*(uint32_t*)0x20000644 = 0;
*(uint32_t*)0x20000648 = 0xe;
*(uint32_t*)0x2000064c = 0;
*(uint64_t*)0x20000650 = 0x20000000;
memcpy((void*)0x20000000,
"\x40\xf0\x53\x8e\xf0\x47\xb2\x1f\xb6\x00\x68\x30\x55\x00", 14);
*(uint64_t*)0x20000658 = 0;
*(uint32_t*)0x20000660 = 0;
*(uint32_t*)0x20000664 = 0;
*(uint32_t*)0x20000668 = 0;
*(uint32_t*)0x2000066c = 0;
*(uint64_t*)0x20000670 = 0;
*(uint64_t*)0x20000678 = 0;
*(uint32_t*)0x20000680 = 0;
*(uint32_t*)0x20000684 = 0;
*(uint32_t*)0x20000688 = 0;
syscall(__NR_bpf, /*cmd=*/0xaul, /*arg=*/0x20000640ul, /*size=*/0x50ul);
break;
}
}
int main(void) {
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul,
/*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
loop();
return 0;
}

Remember to run this repro.txt with the command: syz-execprog -repeat
0 ./repro.txt.

=* repro.txt =*
r0 = bpf$MAP_CREATE_CONST_STR(0x0, &(0x7f0000000340)={0x2, 0x4, 0x8,
0x1, 0x80, 0x0}, 0x48)
bpf$MAP_UPDATE_CONST_STR(0x2, &(0x7f0000000180)={{r0,
<r1=>0xffffffffffffffff}, &(0x7f0000000100), &(0x7f0000000140)='%pi6
\x00'}, 0x20)
bpf$MAP_UPDATE_CONST_STR(0x2, &(0x7f0000000440)={{r1},
&(0x7f00000002c0), &(0x7f0000000400)='%pS \x00'}, 0x20)
bpf$BPF_MAP_CONST_STR_FREEZE(0x16, &(0x7f00000000c0)={r1,
<r2=>0xffffffffffffffff}, 0x4)
r3 = bpf$PROG_LOAD(0x5, &(0x7f00000004c0)={0x16, 0x10,
&(0x7f0000000040)=ANY=[@ANYBLOB="18000000000000000000000000000000b7080000000000007b8af8ff00000000b7080000ffff0b867b8af0ff00000000bfa100000000000007010000f8ffffffbfa400000000000007040000f0feffffb70200000800000018230000",
@ANYRES32=r2, @ANYBLOB="0000000000000000b70500000800000085000000a500000095"],
&(0x7f0000000600)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
0x90)
bpf$BPF_PROG_TEST_RUN(0xa, &(0x7f0000000640)={r3, 0x0, 0xe, 0x0,
&(0x7f0000000000)="40f0538ef047b21fb60068305500", 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0}, 0x50)

and see also in
https://gist.github.com/xrivendell7/baaee5029b1b1d05c66888c29fc1843f.
BTW, this bug maybe similar to this one:
https://syzkaller.appspot.com/bug?extid=c2dc95f7d0825a145992

I hope it helps.
Best regards!
xingwei Lee