Re: [PATCH AUTOSEL 3.18 6/6] ubifs: Check for name being NULL while mounting

[Sasha Levin <sashal@kernel.org>]

On Fri, Oct 05, 2018 at 06:24:42PM +0200, Richard Weinberger wrote:
>Sasha,
>
>Am Freitag, 5. Oktober 2018, 18:17:50 CEST schrieb Sasha Levin:
>> From: Richard Weinberger <richard@nod.at>
>>
>> [ Upstream commit 37f31b6ca4311b94d985fb398a72e5399ad57925 ]
>>
>> The requested device name can be NULL or an empty string.
>> Check for that and refuse to continue. UBIFS has to do this manually
>> since we cannot use mount_bdev(), which checks for this condition.
>>
>> Fixes: 1e51764a3c2ac ("UBIFS: add new flash file system")
>> Reported-by: syzbot+38bd0f7865e5c6379280@syzkaller.appspotmail.com
>> Signed-off-by: Richard Weinberger <richard@nod.at>
>> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
>
>I'm not sure whether it makes sense to apply this patch to stable.
>1. You need to be the real root to hit this code path.
>2. Access is read-only, for an attacker it is useless.
>
>If we look at the code:
>        if (name[0] != 'u' || name[1] != 'b' || name[2] != 'i')
>                return ERR_PTR(-EINVAL);
>
>        /* ubi:NAME method */
>        if ((name[3] == ':' || name[3] == '!') && name[4] != '\0')
>
>name can be NULL, so we access just a few bytes.
>
>Thanks,
>//richard

Hi Richard,

I wasn't really looking at it from a security perspective. My thought
process was that if a user (root or not) is doing action A, expecting
result B but instead unexpectedly sees result C then it's a bug worth
fixing in stable.

If you think it's a risky change for stable I'd be happy to drop it.


--
Thanks,
Sasha