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SubjectRe: [BUG] ALSA: seq: a possible sleep-in-atomic-context bug in snd_virmidi_dev_receive_event()
On Tue, 17 Dec 2019 14:24:21 +0100,
Jia-Ju Bai wrote:
> The driver may sleep while holding a read lock.
> The function call path (from bottom to top) in Linux 4.19 is:
> sound/core/seq/seq_memory.c, 96:
>     copy_from_user in snd_seq_dump_var_event
> sound/core/seq/seq_virmidi.c, 97:
>     snd_seq_dump_var_event in snd_virmidi_dev_receive_event
> sound/core/seq/seq_virmidi.c, 88:
>     _raw_read_lock in snd_virmidi_dev_receive_event

This can't happen. snd_virmidi_dev_receive_event() takes
conditionally either read_lock or rw_sem depending on the atomic
argument. And the data including user-space pointer is handled always
with atomic=1, hence down_read() is used instead of read_lock() here.



> copy_from_user() can sleep at runtime.
> I am not sure how to properly fix this possible bug, so I only report it.
> This bug is found by a static analysis tool STCheck written by myself.
> Best wishes,
> Jia-Ju Bai

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