Messages in this thread | | | From | David Howells <> | Subject | Re: [syzbot] possible deadlock in pipe_write | Date | Mon, 21 Mar 2022 16:03:48 +0000 |
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Jann Horn <jannh@google.com> wrote:
> The syz reproducer is: > > #{"threaded":true,"procs":1,"slowdown":1,"sandbox":"","close_fds":false} > pipe(&(0x7f0000000240)={<r0=>0xffffffffffffffff, <r1=>0xffffffffffffffff}) > pipe2(&(0x7f00000001c0)={0xffffffffffffffff, <r2=>0xffffffffffffffff}, 0x80) > splice(r0, 0x0, r2, 0x0, 0x1ff, 0x0) > vmsplice(r1, &(0x7f00000006c0)=[{&(0x7f0000000080)="b5", 0x1}], 0x1, 0x0) > > That 0x80 is O_NOTIFICATION_PIPE (==O_EXCL). > > It looks like the bug is that when you try to splice between a normal > pipe and a notification pipe, get_pipe_info(..., true) fails, so > splice() falls back to treating the notification pipe like a normal > pipe - so we end up in iter_file_splice_write(), which first locks the > input pipe, then calls vfs_iter_write(), which locks the output pipe. > > I think this probably (?) can't actually lead to deadlocks, since > you'd need another way to nest locking a normal pipe into locking a > watch_queue pipe, but the lockdep annotations don't make that clear.
Is this then a bug/feature in iter_file_splice_write() rather than in the watch queue code, per se?
David
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