From: Greg KH <gregkh@linuxfoundation.org>
To: "Cen Zhang (Microsoft Security FORGE Labs)"
<cenzhang@linux.microsoft.com>
Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz,
jkoolstra@xs4all.nl, neil@brown.name, sandeen@redhat.com,
kees@kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
AutonomousCodeSecurity@microsoft.com, xmei5@asu.edu,
tgopinath@linux.microsoft.com, kys@microsoft.com
Subject: Re: [PATCH] ufs: validate cylinder group free bitmap offset
Date: Wed, 2 Sep 2026 07:53:28 +0200 [thread overview]
Message-ID: <2026090207-threaten-shakiness-a0bc@gregkh> (raw)
In-Reply-To: <20260901180600.10394-1-cenzhang@linux.microsoft.com>
On Tue, Sep 01, 2026 at 02:06:00PM -0400, Cen Zhang (Microsoft Security FORGE Labs) wrote:
> ufs_read_cylinder() copies cg_freeoff from the on-disk cylinder group
> without checking that the free-fragment bitmap fits in the loaded
> cylinder group buffers. A crafted image can place cg_freeoff past those
> buffers so that allocation later indexes ubh->bh[] out of range.
>
> UBSAN: array-index-out-of-bounds in fs/ufs/balloc.c:752:15
> ubh_scanc() fs/ufs/balloc.c:752
> ufs_bitmap_search() fs/ufs/balloc.c
> ufs_alloccg_block() fs/ufs/balloc.c
> ufs_alloc_fragments() fs/ufs/balloc.c
> ufs_new_fragments() fs/ufs/balloc.c
>
> Reject the cylinder group unless the full BITS_TO_BYTES(s_fpg)
> free-fragment bitmap starting at c_freeoff fits in the bytes actually
> loaded for that cylinder group.
Why not fix the userspace fsck tool to fix this instead of working
around it in the kernel?
thanks,
greg k-h
prev parent reply other threads:[~2026-09-02 5:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-01 18:06 [PATCH] ufs: validate cylinder group free bitmap offset Cen Zhang (Microsoft Security FORGE Labs)
2026-09-02 5:53 ` Greg KH [this message]
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