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([2606:6d00:15:e221::5ac]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-52fbe5495easm18663991cf.2.2026.08.28.11.40.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 11:40:22 -0700 (PDT) Message-ID: Subject: Re: [PATCH] media: v4l2-h264: Fix memcmp() size in B1 reference list comparison From: Nicolas Dufresne To: Haotian Zhang , mchehab@kernel.org Cc: boris.brezillon@collabora.com, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 28 Aug 2026 14:40:21 -0400 In-Reply-To: References: <20260828021739.25766-1-vulab@iscas.ac.cn> Autocrypt: addr=nicolas@ndufresne.ca; prefer-encrypt=mutual; keydata=mDMEaCN2ixYJKwYBBAHaRw8BAQdAM0EHepTful3JOIzcPv6ekHOenE1u0vDG1gdHFrChD /e0J05pY29sYXMgRHVmcmVzbmUgPG5pY29sYXNAbmR1ZnJlc25lLmNhPoicBBMWCgBEAhsDBQsJCA cCAiICBhUKCQgLAgQWAgMBAh4HAheABQkJZfd1FiEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrjo CGQEACgkQ2UGUUSlgcvQlQwD/RjpU1SZYcKG6pnfnQ8ivgtTkGDRUJ8gP3fK7+XUjRNIA/iXfhXMN abIWxO2oCXKf3TdD7aQ4070KO6zSxIcxgNQFtDFOaWNvbGFzIER1ZnJlc25lIDxuaWNvbGFzLmR1Z nJlc25lQGNvbGxhYm9yYS5jb20+iJkEExYKAEECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4 AWIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCaCyyxgUJCWX3dQAKCRDZQZRRKWBy9ARJAP96pFmLffZ smBUpkyVBfFAf+zq6BJt769R0al3kHvUKdgD9G7KAHuioxD2v6SX7idpIazjzx8b8rfzwTWyOQWHC AAS0LU5pY29sYXMgRHVmcmVzbmUgPG5pY29sYXMuZHVmcmVzbmVAZ21haWwuY29tPoiZBBMWCgBBF iEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrGYCGwMFCQll93UFCwkIBwICIgIGFQoJCAsCBBYCAw ECHgcCF4AACgkQ2UGUUSlgcvRObgD/YnQjfi4+L8f4fI7p1pPMTwRTcaRdy6aqkKEmKsCArzQBAK8 bRLv9QjuqsE6oQZra/RB4widZPvphs78H0P6NmpIJ Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-unrg0YqCUSdp2BkNKbCj" User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 --=-unrg0YqCUSdp2BkNKbCj Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Le vendredi 28 ao=C3=BBt 2026 =C3=A0 14:31 -0400, Nicolas Dufresne a =C3=A9= crit=C2=A0: > Le vendredi 28 ao=C3=BBt 2026 =C3=A0 10:17 +0800, Haotian Zhang a =C3=A9c= rit=C2=A0: > > In v4l2_h264_build_b_ref_lists(), the B0/B1 list equality > > check passes the entry count builder->num_valid to memcmp() > > instead of a byte size. Since struct v4l2_h264_reference is > > two bytes (fields and index), only half of each list is > > compared, so distinct lists can be wrongly treated as equal > > and trigger an incorrect swap(b1_reflist[0], b1_reflist[1]). > >=20 > > Change the memcmp() size argument to builder->num_valid * > > sizeof(*b1_reflist) so that the full byte length of both > > reference lists is compared. > >=20 > > Fixes: 624922a2739b ("media: v4l2-core: Add helpers to build the H264 P= /B0/B1 reflists") >=20 > This is the wrong commit. It was fine until I broke it 4 years ago it see= ms. > Boris don't do that kind of silly mistake :-S >=20 > commit 2e2c3d6c0ef88ffac0d6b5079ee88cf8408f5f3b > Author: Nicolas Dufresne > Date: Fri May 13 22:29:03 2022 +0200 >=20 > media: h264: Use v4l2_h264_reference for reflist >=20 >=20 > > Signed-off-by: Haotian Zhang > > --- > > drivers/media/v4l2-core/v4l2-h264.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > >=20 > > diff --git a/drivers/media/v4l2-core/v4l2-h264.c b/drivers/media/v4l2-c= ore/v4l2-h264.c > > index c00197d095e7..1b1421caf488 100644 > > --- a/drivers/media/v4l2-core/v4l2-h264.c > > +++ b/drivers/media/v4l2-core/v4l2-h264.c > > @@ -440,7 +440,8 @@ v4l2_h264_build_b_ref_lists(const struct v4l2_h264_= reflist_builder *builder, > > } > > =20 > > if (builder->num_valid > 1 && > > - !memcmp(b1_reflist, b0_reflist, builder->num_valid)) > > + !memcmp(b1_reflist, b0_reflist, > > + builder->num_valid * sizeof(*b1_reflist))) > > swap(b1_reflist[0], b1_reflist[1]); >=20 > And of course this swap need to be replaced. Ignore this one, I should have read the implementation of the swap macro ..= . its working fine for this case: do { typeof(a) __tmp =3D (a); (a) =3D (b); (b) =3D __tmp; } while (0) >=20 > Nicolas >=20 > > =20 > > print_ref_list_b(builder, b0_reflist, 0); --=-unrg0YqCUSdp2BkNKbCj Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCapHWFQAKCRDZQZRRKWBy 9I5FAP4pAojWSgZldIdug90QOouR8PzyNZHFqoGbppt3z6OHigD/cuCfdNQPMyG+ blOFlkaafAtbJA3hoOlfvFE9Jy+ftw4= =wqfg -----END PGP SIGNATURE----- --=-unrg0YqCUSdp2BkNKbCj--