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

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Date:   Fri, 05 Oct 2018 18:24:42 +0200
From:   Richard Weinberger <richard@....at>
To:     Sasha Levin <sashal@...nel.org>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: Re: [PATCH AUTOSEL 3.18 6/6] ubifs: Check for name being NULL while mounting

Sasha,

Am Freitag, 5. Oktober 2018, 18:17:50 CEST schrieb Sasha Levin:
> From: Richard Weinberger <richard@....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@...kaller.appspotmail.com
> Signed-off-by: Richard Weinberger <richard@....at>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.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