From: cuigaosheng <cuigaosheng1@huawei.com>
To: Paul Moore <paul@paul-moore.com>, Jan Kara <jack@suse.cz>,
<cuigaosheng1@huawei.com>
Cc: mszeredi@redhat.com, amir73il@gmail.com,
linux-kernel@vger.kernel.org, eparis@redhat.com,
linux-audit@redhat.com
Subject: Re: [PATCH next] audit: fix potential double free on error path from fsnotify_add_inode_mark
Date: Tue, 23 Aug 2022 10:06:24 +0800 [thread overview]
Message-ID: <ab871457-8754-2d06-20f3-7743289d1ae9@huawei.com> (raw)
In-Reply-To: <CAHC9VhTpLqvZ7PCi3kn1NE6Sq967wLZA1MgnONUVYa0+j_EXbA@mail.gmail.com>
在 2022/8/23 6:49, Paul Moore 写道:
> On Mon, Aug 22, 2022 at 1:59 PM Jan Kara <jack@suse.cz> wrote:
>> On Mon 22-08-22 13:39:23, Paul Moore wrote:
>>> On Mon, Aug 22, 2022 at 11:20 AM Jan Kara <jack@suse.cz> wrote:
>>>> On Mon 22-08-22 10:34:15, Paul Moore wrote:
>>>>> On Mon, Aug 22, 2022 at 4:50 AM Jan Kara <jack@suse.cz> 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@huawei.com>
>>>>>> Good spotting! The patch looks good to me. Feel free to add:
>>>>>>
>>>>>> Reviewed-by: Jan Kara <jack@suse.cz>
>>>>>>
>>>>>>> ---
>>>>>>> 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!
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prev parent reply other threads:[~2022-08-23 2:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-22 2:29 [PATCH next] audit: fix potential double free on error path from fsnotify_add_inode_mark Gaosheng Cui
2022-08-22 8:50 ` Jan Kara
2022-08-22 14:34 ` Paul Moore
2022-08-22 15:20 ` Jan Kara
2022-08-22 17:39 ` Paul Moore
2022-08-22 17:59 ` Jan Kara
2022-08-22 22:49 ` Paul Moore
2022-08-23 2:06 ` cuigaosheng [this message]
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