Re: [PATCH next] audit: fix potential double free on error path from fsnotify_add_inode_mark
From: cuigaosheng
Date: Mon Aug 22 2022 - 22:06:38 EST
在 2022/8/23 6:49, Paul Moore 写道:
On Mon, Aug 22, 2022 at 1:59 PM Jan Kara <jack@xxxxxxx> wrote:
On Mon 22-08-22 13:39:23, Paul Moore wrote:
On Mon, Aug 22, 2022 at 11:20 AM Jan Kara <jack@xxxxxxx> wrote:
On Mon 22-08-22 10:34:15, Paul Moore wrote:
On Mon, Aug 22, 2022 at 4:50 AM Jan Kara <jack@xxxxxxx> wrote:
On Mon 22-08-22 10:29:05, Gaosheng Cui wrote:
Audit_alloc_mark() assign pathname to audit_mark->path, on error path
from fsnotify_add_inode_mark(), fsnotify_put_mark will free memory
of audit_mark->path, but the caller of audit_alloc_mark will free
the pathname again, so there will be double free problem.
Fix this by resetting audit_mark->path to NULL pointer on error path
from fsnotify_add_inode_mark().
Fixes: 7b1293234084d ("fsnotify: Add group pointer in fsnotify_init_mark()")
Signed-off-by: Gaosheng Cui <cuigaosheng1@xxxxxxxxxx>
Good spotting! The patch looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
kernel/audit_fsnotify.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/audit_fsnotify.c b/kernel/audit_fsnotify.c
index 6432a37ac1c9..c565fbf66ac8 100644
--- a/kernel/audit_fsnotify.c
+++ b/kernel/audit_fsnotify.c
@@ -102,6 +102,7 @@ struct audit_fsnotify_mark *audit_alloc_mark(struct audit_krule *krule, char *pa
ret = fsnotify_add_inode_mark(&audit_mark->mark, inode, 0);
if (ret < 0) {
+ audit_mark->path = NULL;
fsnotify_put_mark(&audit_mark->mark);
As I'm tracing the code path from audit through fsnotify, and back
into audit, I'm wondering if we still have a problem. When
fsnotify_add_inode_mark() fails it will end up freeing not just
audit_mark->path, but audit_mark itself via audit_fsnotify_mark_free()
(via a call into fsnotify_put_mark()), yes?
I don't think so. fsnotify_add_mark_locked() will call fsnotify_put_mark()
but that is just a counter part to fsnotify_get_mark() a few lines above.
The caller of fsnotify_add_inode_mark() still holds its own mark reference
which prevents mark from being freed.
Okay, that sounds reasonable, but I'm still looking for a code path
that only frees audit_mark:path and not the audit_mark itself. What
am I not seeing?
The callers of audit_alloc_mark() call kfree(path) if audit_alloc_mark()
returns error (which is a sensible thing because in some cases path indeed
needs freeing).
Of course! Thanks for that, I think I got a bit of tunnel vision on
this for some reason.
I'll merge this into audit/stable-6.0 now and once testing is complete
I'll send it up to Linus. Thanks everyone!
Thanks for taking the time to review this patch. Thanks everyone!