Date: Sat, 11 May 2024 22:45:06 +0800
From: lee bruce <xrivendell7@...il.com>
To: syzbot+68619f9e9e69accd8e0a@...kaller.appspotmail.com, luto@...nel.org, 
	peterz@...radead.org, Thomas Gleixner <tglx@...utronix.de>, ebiederm@...ssion.com
Cc: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	clf700383@...il.com, michael.christie@...cle.com, mst@...hat.com, 
	Christian Brauner <brauner@...nel.org>
Subject: Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in
 kill_orphaned_pgrp (2)

Hello, I found a reproducer for this bug.

If you fix this issue, please add the following tag to the commit:
Reported-by: xingwei lee <xrivendell7@...il.com>
Reported-by: lingfei cheng <clf700383@...il.com>

I use the same kernel as syzbot instance
Kernel Commit: upstream dccb07f2914cdab2ac3a5b6c98406f765acab803
Kernel Config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=6d14c12b661fb43
with KASAN enabled

Since the same title bug is triggered in
https://syzkaller.appspot.com/bug?id=70492b96ff47ff70cfc433be100586119310670b.
I make a simple RCA.
In the old-syzbot instance the bug still trigger the title "KASAN:
slab-use-after-free Read in kill_orphaned_pgrp” and in the lastest
syzbot the bug report as

TITLE: WARNING in signal_wake_up_state
------------[ cut here ]------------
WARNING: CPU: 3 PID: 8591 at kernel/signal.c:762
signal_wake_up_state+0xf8/0x130 kernel/signal.c:762
Modules linked in:
CPU: 3 PID: 8591 Comm: file0 Not tainted 6.9.0-rc7-00012-gdccb07f2914c #6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.16.0-2.fc37 04/01/2014
RIP: 0010:signal_wake_up_state+0xf8/0x130 kernel/signal.c:762
Code: 31 c0 31 c9 31 f6 e9 b2 1f 73 0a e8 42 6f 3a 00 48 89 df 5b 41
5e 41 5f 5d 31 c0 31 c9 31 f6 e9 ce 27 0a 00 ec
RSP: 0000:ffffc900154af918 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8880239a0000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880239a0000
R13: ffff88802bd80908 R14: 0000000000000108 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff88823bc80000(0000) knlGS:0000000000000000
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000259fa000 CR4: 0000000000750ef0
PKRU: 55555554
Call Trace:
<TASK>
signal_wake_up include/linux/sched/signal.h:448 [inline]
zap_process fs/coredump.c:373 [inline]
zap_threads fs/coredump.c:392 [inline]
coredump_wait fs/coredump.c:410 [inline]
do_coredump+0x8ff/0x2b60 fs/coredump.c:571
get_signal+0x13fa/0x1740 kernel/signal.c:2896
arch_do_signal_or_restart+0x96/0x870 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
irqentry_exit_to_user_mode+0x79/0x280 kernel/entry/common.c:231
exc_page_fault+0x577/0x8b0 arch/x86/mm/fault.c:1535
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0033:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 002b:00000000ff9bfe10 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>

This is also the reason why there are so many people in my cc list.

I debug this bug for a while and found that when our PoC process call vhost:
vhost_dev_set_owner
 vhost_worker_create
   copy_process

It will call copy_process to create a “vhost-xxxx” thread in workqueue
to run vhost_task_fn.

Also, PoC create a invalid elf “file0" and execute it afterwards.
It is conceivable that execute syscall will fail and kill itself in
put_task_struct prograss.
However, when the workQueue thread “vhost-xxxx” call vhost_task_fn

static int vhost_task_fn(void *data)
{
struct vhost_task *vtsk = data;
bool dead = false;

for (;;) {
bool did_work;

if (!dead && signal_pending(current)) {
struct ksignal ksig;
/*
* Calling get_signal will block in SIGSTOP,
* or clear fatal_signal_pending, but remember
* what was set.
*
* This thread won't actually exit until all
* of the file descriptors are closed, and
* the release function is called.
*/
dead = get_signal(&ksig);
if (dead)
clear_thread_flag(TIF_SIGPENDING);
}

/* mb paired w/ vhost_task_stop */
set_current_state(TASK_INTERRUPTIBLE);

if (test_bit(VHOST_TASK_FLAGS_STOP, &vtsk->flags)) {
__set_current_state(TASK_RUNNING);
break;
}

did_work = vtsk->fn(vtsk->data);
if (!did_work)
schedule();
}

complete(&vtsk->exited);
do_exit(0);
}

I found, which seems a bit strange but I’m not sure:

gef> bt
#0 kill_orphaned_pgrp (tsk=0xffff888107833780, parent=parent@...ry=0x0
<fixed_percpu_data>) at ./include/linux/sched/signal.h:694
#1 0xffffffff811ff54d in exit_notify (group_dead=0x1,
tsk=0xffff888245e0d340) at kernel/exit.c:737
#2 do_exit (code=code@...ry=0x0) at kernel/exit.c:894
#3 0xffffffff812331ea in vhost_task_fn (data=0xffff88824570c700) at
kernel/vhost_task.c:61
#4 0xffffffff810d7f7c in ret_from_fork (prev=<optimized out>,
regs=0xffffc90007eaff58, fn=0xffffffff81233110 <vhost_task_fn>,
fn_arg=0xffff88824570c700)
at arch/x86/kernel/process.c:147
#5 0xffffffff81002431 in ret_from_fork_asm () at arch/x86/entry/entry_64.S:304
#6 0x00007fff1f50a958 in ?? ()
#7 0x00007fff1f50a870 in ?? ()
#8 0x0000000000000011 in fixed_percpu_data ()
#9 0xffffffffffffffb0 in ?? ()
#10 0x00007fe268ae3220 in ?? ()
#11 0x00007fe268ae36c0 in ?? ()
#12 0x0000000000000203 in ?? ()
#13 0x0000000000000000 in ?? ()
gef> p tsk->comm
$64 = "PoC", '\\000' <repeats 12 times>


the vhost_task_fn trying to call kill_orphaned_pgrp to and cause a UAF
because the PoC task is feed by idle in the KASAN report.

I don't know if my analysis is correct, please feel free to correct me.


=* repro.c =*
#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.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>

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[2] = {0xffffffffffffffff, 0xffffffffffffffff};

void execute_call(int call) {
 intptr_t res = 0;
 switch (call) {
   case 0:
     memcpy((void*)0x20000280, "./file0\000", 8);
     res = syscall(__NR_creat, /*file=*/0x20000280ul,
                   /*mode=*/0xecf86c37d53049ccul);
     if (res != -1) r[0] = res;
     break;
   case 1:
     *(uint8_t*)0x20000440 = 0x7f;
     *(uint8_t*)0x20000441 = 0x45;
     *(uint8_t*)0x20000442 = 0x4c;
     *(uint8_t*)0x20000443 = 0x46;
     *(uint8_t*)0x20000444 = 0;
     *(uint8_t*)0x20000445 = 0;
     *(uint8_t*)0x20000446 = 0;
     *(uint8_t*)0x20000447 = 0;
     *(uint64_t*)0x20000448 = 0;
     *(uint16_t*)0x20000450 = 2;
     *(uint16_t*)0x20000452 = 0x3e;
     *(uint32_t*)0x20000454 = 0;
     *(uint32_t*)0x20000458 = 0;
     *(uint32_t*)0x2000045c = 0x38;
     *(uint32_t*)0x20000460 = 0;
     *(uint32_t*)0x20000464 = 0;
     *(uint16_t*)0x20000468 = 0xeb0;
     *(uint16_t*)0x2000046a = 0x20;
     *(uint16_t*)0x2000046c = 2;
     *(uint16_t*)0x2000046e = 0;
     *(uint16_t*)0x20000470 = 0;
     *(uint16_t*)0x20000472 = 0;
     *(uint32_t*)0x20000478 = 0;
     *(uint32_t*)0x2000047c = 0;
     *(uint32_t*)0x20000480 = 0;
     *(uint32_t*)0x20000484 = 0;
     *(uint32_t*)0x20000488 = 0;
     *(uint32_t*)0x2000048c = 0;
     *(uint32_t*)0x20000490 = 0;
     *(uint32_t*)0x20000494 = 0;
     memset((void*)0x20000498, 0, 256);
     memset((void*)0x20000598, 0, 256);
     memset((void*)0x20000698, 0, 256);
     memset((void*)0x20000798, 0, 256);
     memset((void*)0x20000898, 0, 256);
     memset((void*)0x20000998, 0, 256);
     memset((void*)0x20000a98, 0, 256);
     syscall(__NR_write, /*fd=*/r[0], /*data=*/0x20000440ul, /*len=*/0x758ul);
     break;
   case 2:
     syscall(__NR_close, /*fd=*/r[0]);
     break;
   case 3:
     memcpy((void*)0x20000000, "/dev/vhost-net\000", 15);
     res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul,
                   /*file=*/0x20000000ul, /*flags=*/2ul, /*mode=*/0ul);
     if (res != -1) r[1] = res;
     break;
   case 4:
     syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/0xaf01, /*v=*/0ul);
     break;
   case 5:
     memcpy((void*)0x20000400, "./file0\000", 8);
     syscall(__NR_execve, /*file=*/0x20000400ul, /*argv=*/0ul, /*envp=*/0ul);
     break;
 }
}
int main(void) {
 syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 loop();
 return 0;
}

=* repro.txt =*
r0 = creat(&(0x7f0000000280)='./file0\x00', 0xecf86c37d53049cc)
write$binfmt_elf32(r0, &(0x7f0000000440)={{0x7f, 0x45, 0x4c, 0x46,
0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x3e, 0x0, 0x0, 0x38, 0x0, 0x0, 0xeb0,
0x20, 0x2}, [{}], "", ['\x00', '\x00', '\x00', '\x00', '\x00', '\x00',
'\x00']}, 0x758)
close(r0)
r1 = openat$vnet(0xffffffffffffff9c, &(0x7f0000000000), 0x2, 0x0)
ioctl$int_in(r1, 0x40000000af01, 0x0)
execve(&(0x7f0000000400)='./file0\x00', 0x0, 0x0)

and see also in
https://gist.github.com/xrivendell7/c1540d905cdbcc43fc134a76dd364f6d

I hope it helps.
Best regards

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