* kernel BUG at fs/inode.c:LINE! (2)
@ 2020-08-28 13:18 syzbot
2020-08-28 15:38 ` Al Viro
0 siblings, 1 reply; 4+ messages in thread
From: syzbot @ 2020-08-28 13:18 UTC (permalink / raw)
To: axboe, linux-fsdevel, linux-kernel, maz, oleg, peterz,
syzkaller-bugs, viro
Hello,
syzbot found the following issue on:
HEAD commit: d012a719 Linux 5.9-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15aa650e900000
kernel config: https://syzkaller.appspot.com/x/.config?x=891ca5711a9f1650
dashboard link: https://syzkaller.appspot.com/bug?extid=c92c93d1f1aaaacdb9db
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12ecb939900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140a19a9900000
The issue was bisected to:
commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682
Author: Marc Zyngier <maz@kernel.org>
Date: Wed Aug 19 16:12:17 2020 +0000
epoll: Keep a reference on files added to the check list
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16a50519900000
final oops: https://syzkaller.appspot.com/x/report.txt?x=15a50519900000
console output: https://syzkaller.appspot.com/x/log.txt?x=11a50519900000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c92c93d1f1aaaacdb9db@syzkaller.appspotmail.com
Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")
------------[ cut here ]------------
kernel BUG at fs/inode.c:1668!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 29571 Comm: syz-executor709 Not tainted 5.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:iput+0x6d8/0x6e0 fs/inode.c:1668
Code: ef ff e9 1a fc ff ff 44 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c c8 fe ff ff 4c 89 ef e8 a2 51 ef ff e9 bb fe ff ff e8 68 77 af ff <0f> 0b 66 0f 1f 44 00 00 55 41 57 41 56 53 48 89 f5 48 89 fb 49 bf
RSP: 0018:ffffc9000e25fda8 EFLAGS: 00010293
RAX: ffffffff81c580b8 RBX: ffff888085112600 RCX: ffff8880a6eea200
RDX: 0000000000000000 RSI: 0000000000000040 RDI: 0000000000000000
RBP: 0000000000000040 R08: ffffffff81c57a40 R09: ffffed10116fe44d
R10: ffffed10116fe44d R11: 0000000000000000 R12: 1ffff11010a224ac
R13: dffffc0000000000 R14: ffff888085112600 R15: ffff888085112560
FS: 0000000001665880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 000000008f752000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__sock_release net/socket.c:608 [inline]
sock_close+0x1c3/0x260 net/socket.c:1277
__fput+0x34f/0x7b0 fs/file_table.c:281
task_work_run+0x137/0x1c0 kernel/task_work.c:141
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop kernel/entry/common.c:140 [inline]
exit_to_user_mode_prepare+0xfa/0x1b0 kernel/entry/common.c:167
syscall_exit_to_user_mode+0x5e/0x1a0 kernel/entry/common.c:242
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4058e1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 6a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 b3 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffc7ca575a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 00000000004058e1
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 0000000000000007 R08: 0000000120080522 R09: 0000000120080522
R10: 0000000120080522 R11: 0000000000000293 R12: 00000000006dbc5c
R13: 0000000000000001 R14: 00000000006dbc50 R15: 0000000000000064
Modules linked in:
---[ end trace 35240c511479d576 ]---
RIP: 0010:iput+0x6d8/0x6e0 fs/inode.c:1668
Code: ef ff e9 1a fc ff ff 44 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c c8 fe ff ff 4c 89 ef e8 a2 51 ef ff e9 bb fe ff ff e8 68 77 af ff <0f> 0b 66 0f 1f 44 00 00 55 41 57 41 56 53 48 89 f5 48 89 fb 49 bf
RSP: 0018:ffffc9000e25fda8 EFLAGS: 00010293
RAX: ffffffff81c580b8 RBX: ffff888085112600 RCX: ffff8880a6eea200
RDX: 0000000000000000 RSI: 0000000000000040 RDI: 0000000000000000
RBP: 0000000000000040 R08: ffffffff81c57a40 R09: ffffed10116fe44d
R10: ffffed10116fe44d R11: 0000000000000000 R12: 1ffff11010a224ac
R13: dffffc0000000000 R14: ffff888085112600 R15: ffff888085112560
FS: 0000000001665880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 000000008f752000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: kernel BUG at fs/inode.c:LINE! (2)
2020-08-28 13:18 kernel BUG at fs/inode.c:LINE! (2) syzbot
@ 2020-08-28 15:38 ` Al Viro
2020-08-28 17:54 ` Al Viro
0 siblings, 1 reply; 4+ messages in thread
From: Al Viro @ 2020-08-28 15:38 UTC (permalink / raw)
To: syzbot
Cc: axboe, linux-fsdevel, linux-kernel, maz, oleg, peterz, syzkaller-bugs
On Fri, Aug 28, 2020 at 06:18:17AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: d012a719 Linux 5.9-rc2
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15aa650e900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=891ca5711a9f1650
> dashboard link: https://syzkaller.appspot.com/bug?extid=c92c93d1f1aaaacdb9db
> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12ecb939900000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140a19a9900000
Trying to reproduce...
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: kernel BUG at fs/inode.c:LINE! (2)
2020-08-28 15:38 ` Al Viro
@ 2020-08-28 17:54 ` Al Viro
2020-08-29 15:55 ` Al Viro
0 siblings, 1 reply; 4+ messages in thread
From: Al Viro @ 2020-08-28 17:54 UTC (permalink / raw)
To: syzbot
Cc: axboe, linux-fsdevel, linux-kernel, maz, oleg, peterz, syzkaller-bugs
On Fri, Aug 28, 2020 at 04:38:25PM +0100, Al Viro wrote:
> On Fri, Aug 28, 2020 at 06:18:17AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: d012a719 Linux 5.9-rc2
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15aa650e900000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=891ca5711a9f1650
> > dashboard link: https://syzkaller.appspot.com/bug?extid=c92c93d1f1aaaacdb9db
> > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12ecb939900000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140a19a9900000
>
> Trying to reproduce...
OK, I think I see what's going on. ep_loop_check_proc() runs into an already
doomed file that has already committed to getting killed (->f_count is already
at 0), but still hadn't gotten through its epitems removal (e.g. has its
eventpoll_release_file() sitting there trying to get epmutex).
Blindly bumping refcount here is worse than useless. Try this, to verify that
this is what's going on; it's _not_ a proper fix, but it should at least tell
if we have something else going on.
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index e0decff22ae2..4590223b2de9 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1995,7 +1995,7 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
* during ep_insert().
*/
if (list_empty(&epi->ffd.file->f_tfile_llink)) {
- get_file(epi->ffd.file);
+ if (get_file_rcu(epi->ffd.file))
list_add(&epi->ffd.file->f_tfile_llink,
&tfile_check_list);
}
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: kernel BUG at fs/inode.c:LINE! (2)
2020-08-28 17:54 ` Al Viro
@ 2020-08-29 15:55 ` Al Viro
0 siblings, 0 replies; 4+ messages in thread
From: Al Viro @ 2020-08-29 15:55 UTC (permalink / raw)
To: syzbot
Cc: axboe, linux-fsdevel, linux-kernel, maz, oleg, peterz, syzkaller-bugs
On Fri, Aug 28, 2020 at 06:54:13PM +0100, Al Viro wrote:
> On Fri, Aug 28, 2020 at 04:38:25PM +0100, Al Viro wrote:
> > On Fri, Aug 28, 2020 at 06:18:17AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: d012a719 Linux 5.9-rc2
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15aa650e900000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=891ca5711a9f1650
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=c92c93d1f1aaaacdb9db
> > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12ecb939900000
> > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=140a19a9900000
> >
> > Trying to reproduce...
>
> OK, I think I see what's going on. ep_loop_check_proc() runs into an already
> doomed file that has already committed to getting killed (->f_count is already
> at 0), but still hadn't gotten through its epitems removal (e.g. has its
> eventpoll_release_file() sitting there trying to get epmutex).
>
> Blindly bumping refcount here is worse than useless. Try this, to verify that
> this is what's going on; it's _not_ a proper fix, but it should at least tell
> if we have something else going on.
... and what I think is the right way to fix the original race is (on top of
mainline) this:
[PATCH] Use list_empty_careful() in eventpoll_release()
... to avoid races with list_del_init() in clear_tfile_check_list().
Get rid of pinning files on check list in eventpoll.c - it's not needed
there.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index e0decff22ae2..39eae45bff18 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1995,7 +1995,6 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
* during ep_insert().
*/
if (list_empty(&epi->ffd.file->f_tfile_llink)) {
- get_file(epi->ffd.file);
list_add(&epi->ffd.file->f_tfile_llink,
&tfile_check_list);
}
@@ -2042,7 +2041,6 @@ static void clear_tfile_check_list(void)
file = list_first_entry(&tfile_check_list, struct file,
f_tfile_llink);
list_del_init(&file->f_tfile_llink);
- fput(file);
}
INIT_LIST_HEAD(&tfile_check_list);
}
@@ -2206,7 +2204,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
if (ep_loop_check(ep, tf.file) != 0)
goto error_tgt_fput;
} else {
- get_file(tf.file);
list_add(&tf.file->f_tfile_llink,
&tfile_check_list);
}
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 8f000fada5a4..e2bdefd90cf8 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -46,11 +46,9 @@ static inline void eventpoll_release(struct file *file)
* Fast check to avoid the get/release of the semaphore. Since
* we're doing this outside the semaphore lock, it might return
* false negatives, but we don't care. It'll help in 99.99% of cases
- * to avoid the semaphore lock. False positives simply cannot happen
- * because the file in on the way to be removed and nobody ( but
- * eventpoll ) has still a reference to this file.
+ * to avoid the semaphore lock.
*/
- if (likely(list_empty(&file->f_ep_links)))
+ if (likely(list_empty_careful(&file->f_ep_links)))
return;
/*
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-08-29 15:56 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2020-08-28 13:18 kernel BUG at fs/inode.c:LINE! (2) syzbot
2020-08-28 15:38 ` Al Viro
2020-08-28 17:54 ` Al Viro
2020-08-29 15:55 ` Al Viro
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