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AHgh+RoN/gWIglnFN4haZrYJFneXDfVJHZOfcxTZgWviE7JiPcox5wWUZCU7OVa4yzo7g0+d/qqo81BKJ+ai6bk=@vger.kernel.org X-Gm-Message-State: AOJu0Yxvl6fYlduOAmtcgypdZPgIyaKF4gNUg3NZE9Wm/fTwA4AKTDsF tncuTBKcFLMtU3m5PUwvFvEqXbx6Jmit1b//buKB9cTEsGhH4Dv/rM3mSH9GJxQce550vIFmE3P qSnHsO9SS2E3epGznrWxhf7N9d50L+F0= X-Gm-Gg: AR+sD12kjLsHMkNa7z6KQs34tvsvxEP/xNHy8l6aXQ3q6BHnbAyf5Y4dBFxYn5kly/x 5VADybLUoPMV30HneTqAp/XO9h8+0l6JWqDFAgFmRu5NxvgiEbWfLHOhO5KfGpgM+3jK7cF6/vs 7IFy5wri7s3FFZ0TAaD04SGi3MBwk7bbkK/94ngUMcMojaKVcIMTXs4fe9sY0+VHV+LIsLKHCmE rRmsdLRxbHDt6I2KUolRMIZ6D4gP6a4N0BJDT9AW9igGqppYXnM2EaCUC08cEOc37NAPspetG+l O4qy5HgfZWQbU4AqGcCTqTav1jeXxz24pURRn2ZmB7QmuQ== X-Received: by 2002:a05:6402:44da:b0:69a:b38d:403c with SMTP id 4fb4d7f45d1cf-6a0a7c6b782mr1461832a12.7.1785572792620; Sat, 01 Aug 2026 01:26:32 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260726070122.2407344-1-zirajs7@gmail.com> In-Reply-To: From: =?UTF-8?B?7J6E7KSA7ISc?= Date: Sat, 1 Aug 2026 17:26:21 +0900 X-Gm-Features: AUfX_my-pYFZ-XPP8zv7R4daRh3IROnR0mixq9YUOBqskq85YnbAh1a2KU5vdAg Message-ID: Subject: Re: [PATCH bpf] bpf: Reject negative optlen in cgroup getsockopt hook To: Emil Tsalapatis Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Stanislav Fomichev , Song Liu , Yonghong Song , Jiri Olsa , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Sechang Lim Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Thanks for the review. The reproducer already sets ctx->optlen to a negative value (-11) in the cgroup BPF program: /* ctx->optlen =3D -11; */ BPF_MOV64_IMM(BPF_REG_2, -11), BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_2, offsetof(struct bpf_sockopt, optlen)), https://gist.github.com/ZirAjs/a177ec6d8f2c8ed7d93edca6313a9255 The PASS/FAIL output only checks the behavior before and after applying the patch. Without the patch, the negative value reaches copy_to_sockptr() and triggers the warning. With the patch, getsockopt() rejects it with -EFAULT. Would you prefer that I include the reproducer directly in the patch submission rather than only linking to the gist? On Thu, Jul 30, 2026 at 6:36=E2=80=AFAM Emil Tsalapatis wrote: > > On Sun Jul 26, 2026 at 3:01 AM EDT, Junseo Lim wrote: > > A cgroup getsockopt BPF program can shrink ctx->optlen after the > > kernel getsockopt handler has run. The kernel-buffer variant, used by > > TCP_ZEROCOPY_RECEIVE, only rejects values larger than the original > > length. > > > > If BPF writes a negative optlen, that value is accepted and propagated > > back to the TCP getsockopt code. It can then be passed to > > copy_to_sockptr() as a size_t and trigger the hardened usercopy > > bytes > INT_MAX warning. > > > > Reject negative ctx.optlen in __cgroup_bpf_run_filter_getsockopt_kern()= , > > matching the lower-bound validation already present in the sockptr-base= d > > getsockopt hook. > > > > Fixes: 9cacf81f8161 ("bpf: Remove extra lock_sock for TCP_ZEROCOPY_RECE= IVE") > > Signed-off-by: Junseo Lim > > Reviewed-by: Emil Tsalapatis > > It'd be worth resending with a reproducer setting optlen to negative. > > > --- > > Reproducer and warning: > > https://gist.github.com/ZirAjs/a177ec6d8f2c8ed7d93edca6313a9255 > > > > Tested by building and booting the patched kernel. The reproducer > > returns -EFAULT and no longer triggers the hardened usercopy warning. > > > > kernel/bpf/cgroup.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > > index 4355ccb78a9c..c04a244fe2e6 100644 > > --- a/kernel/bpf/cgroup.c > > +++ b/kernel/bpf/cgroup.c > > @@ -2235,7 +2235,7 @@ int __cgroup_bpf_run_filter_getsockopt_kern(struc= t sock *sk, int level, > > if (ret < 0) > > return ret; > > > > - if (ctx.optlen > *optlen) > > + if (ctx.optlen > *optlen || ctx.optlen < 0) > > return -EFAULT; > > > > /* BPF programs can shrink the buffer, export the modifications. >