| From | Ben Hutchings <> | Date | Mon, 06 Nov 2017 23:03:07 +0000 | Subject | [PATCH 3.2 036/147] audit: Fix use after free in audit_remove_watch_rule() |
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3.2.95-rc1 review patch. If anyone has any objections, please let me know.
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From: Jan Kara <jack@suse.cz>
commit d76036ab47eafa6ce52b69482e91ca3ba337d6d6 upstream.
audit_remove_watch_rule() drops watch's reference to parent but then continues to work with it. That is not safe as parent can get freed once we drop our reference. The following is a trivial reproducer:
mount -o loop image /mnt touch /mnt/file auditctl -w /mnt/file -p wax umount /mnt auditctl -D <crash in fsnotify_destroy_mark()>
Grab our own reference in audit_remove_watch_rule() earlier to make sure mark does not get freed under us.
Reported-by: Tony Jones <tonyj@suse.de> Signed-off-by: Jan Kara <jack@suse.cz> Tested-by: Tony Jones <tonyj@suse.de> Signed-off-by: Paul Moore <paul@paul-moore.com> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- kernel/audit_watch.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
--- a/kernel/audit_watch.c +++ b/kernel/audit_watch.c @@ -471,13 +471,15 @@ void audit_remove_watch_rule(struct audi list_del(&krule->rlist); if (list_empty(&watch->rules)) { + /* + * audit_remove_watch() drops our reference to 'parent' which + * can get freed. Grab our own reference to be safe. + */ + audit_get_parent(parent); audit_remove_watch(watch); - - if (list_empty(&parent->watches)) { - audit_get_parent(parent); + if (list_empty(&parent->watches)) fsnotify_destroy_mark(&parent->mark); - audit_put_parent(parent); - } + audit_put_parent(parent); } }
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