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bh=IyGOw4U4ix5P0wWcI0DA7kOT20fFy32UpdeDywIjYwA=; b=dGCzR00m9UIpEy5m7VlUEVwJdxrJnrQ+CrWjVndRowk/uUUXXg3pBKqXZNXccj48IH0YvJ dzbZDs9RE2dOBwLcSqs725Trr6vV9p/KeIVJM4nxFvqJMHMnGsmE/9hkDw3rCYqwXBZOOr Gq4ngQkcPJXqQXqqbWoRnbeuxo9EzXmHZXLivj6y+t5Bw9U0nldC++JSJl7Bdt8XYbxTR7 cxvYC5HCYi5ale2ogffV1bwiWhLD0wRsM+NgRzcH8yUB+LqyTtqHgkPrCOtXYA5XfnkA1U jLa1ed52EwcN/+vjtXW5mCskKLIZVqKEAgYMO7Shf6TmN8SPS2CTzdMsjGrfFw== From: Miquel Raynal To: Griffin Kroah-Hartman Cc: Richard Weinberger , Vignesh Raghavendra , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mtd: parsers: afs: add size check to v2 partition In-Reply-To: <20260824-mtd_break_looper-v1-1-e46d7f02faab@kroah.com> (Griffin Kroah-Hartman's message of "Mon, 24 Aug 2026 15:50:27 +0200") References: <20260824-mtd_break_looper-v1-1-e46d7f02faab@kroah.com> User-Agent: mu4e 1.12.12; emacs 30.2 Date: Tue, 25 Aug 2026 15:42:35 +0200 Message-ID: <87cxv6gvuc.fsf@bootlin.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Last-TLS-Session-Version: TLSv1.3 Hello Griffin, Thanks for the patch! On 24/08/2026 at 15:50:27 +02, Griffin Kroah-Hartman wr= ote: > Add a size check to the loop in afs_parse_v2_partition(), avoiding > walking out of the imginfo[] array bounds if a malicious packet fakes a "packet" refers to network wording, whereas here, in the MTD world, we would rather talk about a malicious image. > large region count. > > Assisted-by: gkh_clanker_t1000 > Signed-off-by: Griffin Kroah-Hartman I guess such a fix would require a Fixes tag, as well as Cc'ing the stable@vger.kernel.org alias. > --- > drivers/mtd/parsers/afs.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/drivers/mtd/parsers/afs.c b/drivers/mtd/parsers/afs.c > index 26116694c821..2c6f8768312c 100644 > --- a/drivers/mtd/parsers/afs.c > +++ b/drivers/mtd/parsers/afs.c > @@ -287,12 +287,18 @@ static int afs_parse_v2_partition(struct mtd_info *= mtd, > block_start, block_end); >=20=20 > for (i =3D 0; i < region_count; i++) { > - u32 region_load_addr =3D imginfo[pad + 3 + i*4]; > - u32 region_size =3D imginfo[pad + 4 + i*4]; > - u32 region_offset =3D imginfo[pad + 5 + i*4]; > + u32 region_load_addr; > + u32 region_size; > + u32 region_offset; > u32 region_start; > u32 region_end; >=20=20 > + if (pad + 5 + i*4 >=3D ARRAY_SIZE(imginfo)) > + break; > + region_load_addr =3D imginfo[pad + 3 + i*4]; > + region_size =3D imginfo[pad + 4 + i*4]; > + region_offset =3D imginfo[pad + 5 + i*4]; > + Looking at the code, I see that just above the loop there is an actual check bailing out early in case the region count is overly big. In practice: - pad can only be 0, 1 or 2 - imginfo array size is 36 The check is: if (region_count > (ARRAY_SIZE(imginfo) - pad - 3) / 4) return -EINVAL; And the loop goes at most through: pad + 5 + (region_count - 1) * 4 So the only possibilities are: pad | max(region_count) | max(index) ----+-------------------+----------- 0 | 8 | 33 1 | 8 | 34 2 | 7 | 31 It seems like none of those situations could actually lead to a reachable/exploitable bug. So while I understand the wish for a more defensive hardening, the check you add seems redundant. I would therefore suggest to just keep the driver as-is. Thanks, Miqu=C3=A8l