Taking an extra file reference before call vfs_poll(), else
the file may be released by aio_poll_wake() if an expected
event is triggered immediately (e.g., by the close of a
pair of pipes) after the return of vfs_poll(), and we may
hit a use-after-free splat as shown below:
BUG: KASAN: use-after-free in perf_trace_lock_acquire+0x3ab/0x570
Read of size 8 at addr ffff888379bfd4b0 by task syz-executor.1/4953
CPU: 0 PID: 4953 Comm: syz-executor.1 Not tainted 4.19.24
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xca/0x13e lib/dump_stack.c:113
print_address_description+0x79/0x330 mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report+0x18a/0x2e0 mm/kasan/report.c:412
trace_event_get_offsets_lock_acquire include/trace/events/lock.h:13 [inline]
perf_trace_lock_acquire+0x3ab/0x570 include/trace/events/lock.h:13
trace_lock_acquire include/trace/events/lock.h:13 [inline]
lock_acquire+0x202/0x310 kernel/locking/lockdep.c:3899
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2c/0x40 kernel/locking/spinlock.c:144
spin_lock include/linux/spinlock.h:329 [inline]
aio_poll fs/aio.c:1750 [inline]
io_submit_one+0xb90/0x1b30 fs/aio.c:1853
__do_sys_io_submit fs/aio.c:1919 [inline]
__se_sys_io_submit fs/aio.c:1890 [inline]
__x64_sys_io_submit+0x19b/0x500 fs/aio.c:1890
do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
......
Allocated by task 4953:
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xa0/0xd0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x12f/0x2d0 mm/slub.c:2733
kmalloc include/linux/slab.h:513 [inline]
kzalloc include/linux/slab.h:707 [inline]
alloc_pipe_info+0xdf/0x410 fs/pipe.c:633
get_pipe_inode fs/pipe.c:712 [inline]
create_pipe_files+0x98/0x780 fs/pipe.c:744
__do_pipe_flags+0x35/0x230 fs/pipe.c:781
do_pipe2+0x87/0x150 fs/pipe.c:829
__do_sys_pipe2 fs/pipe.c:847 [inline]
__se_sys_pipe2 fs/pipe.c:845 [inline]
__x64_sys_pipe2+0x55/0x80 fs/pipe.c:845
do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Freed by task 4952:
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x12e/0x180 mm/kasan/kasan.c:521
slab_free_hook mm/slub.c:1371 [inline]
slab_free_freelist_hook mm/slub.c:1398 [inline]
slab_free mm/slub.c:2953 [inline]
kfree+0xeb/0x2f0 mm/slub.c:3906
put_pipe_info+0xb0/0xd0 fs/pipe.c:556
pipe_release+0x1ab/0x240 fs/pipe.c:577
__fput+0x27f/0x7f0 fs/file_table.c:278
task_work_run+0x136/0x1b0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x1a7/0x1d0 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x461/0x580 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
Cc: stable@xxxxxxxxxxxxxxx [4.19+]
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
fs/aio.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/aio.c b/fs/aio.c
index aaaaf4d12c73..ea2f5de4feac 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1763,6 +1763,12 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
/* one for removal from waitqueue, one for this function */
refcount_set(&aiocb->ki_refcnt, 2);
+ /*
+ * file may be released by aio_poll_wake() if an expected event
+ * is triggered immediately after the return of vfs_poll(), so
+ * an extra reference is needed here to prevent use-after-free.
+ */
+ get_file(req->file);
mask = vfs_poll(req->file, &apt.pt) & req->events;
if (unlikely(!req->head)) {
/* we did not manage to set up a waitqueue, done */
@@ -1788,6 +1794,8 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
spin_unlock_irq(&ctx->ctx_lock);
out:
+ /* release the extra reference for vfs_poll() */
+ fput(req->file);
if (unlikely(apt.error)) {
fput(req->file);
return apt.error;
--
2.16.2.dirty
