fanotify: report full event length for FIONREAD

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fanotify_ioctl(FIONREAD) reports the number of bytes available to read
from the event queue.  It currently accounts only FAN_EVENT_METADATA_LEN
for each queued event.

That underestimates events that carry additional information records, such
as FAN_REPORT_DFID_NAME events.  A userspace program that uses FIONREAD to
size its read buffer can receive a length that is smaller than the next
event.  Reading with that buffer then fails with -EINVAL, while a larger
buffer succeeds and reports a larger metadata.event_len.

Use fanotify_event_len() when summing queued events so FIONREAD includes
all info records.

Fixes: 5e469c830f ("fanotify: copy event fid info to user")
Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
Link: https://patch.msgid.link/20260731021827.602479-1-chenyichong@uniontech.com
Signed-off-by: Jan Kara <jack@suse.cz>

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Yichong Chen 2026-07-31 10:18:27 +08:00 • committed by Jan Kara

parent d7f1cf5be3

commit 68615158c1

1 changed files with 4 additions and 1 deletions

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fs/notify/fanotify/fanotify_user.c

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