fsnotify: Fix NULL ptr deref in fanotify_get_fsid()
fanotify_get_fsid() is reading mark->connector->fsid under srcu. It can happen that it sees mark not fully initialized or mark that is already detached from the object list. In these cases mark->connector can be NULL leading to NULL ptr dereference. Fix the problem by being careful when reading mark->connector and check it for being NULL. Also use WRITE_ONCE when writing the mark just to prevent compiler from doing something stupid. Reported-by: syzbot+15927486a4f1bfcbaf91@syzkaller.appspotmail.com Fixes: 77115225 ("fanotify: cache fsid in fsnotify_mark_connector") Signed-off-by: Jan Kara <jack@suse.cz>
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