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Tue, 11 Aug 2026 07:19:19 -0700 (PDT) From: Junseo Lim To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau Cc: Stanislav Fomichev , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Sechang Lim Subject: [PATCH bpf v2 1/2] bpf: Reject negative optlen in cgroup getsockopt hook Date: Tue, 11 Aug 2026 23:19:07 +0900 Message-ID: <187a4d756275aaaee5d65eecb63c1477b3b66554.1786448307.git.zirajs7@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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-based getsockopt hook. Fixes: 9cacf81f8161 ("bpf: Remove extra lock_sock for TCP_ZEROCOPY_RECEIVE") Reported-by: Sechang Lim Reviewed-by: Emil Tsalapatis Signed-off-by: Junseo Lim --- This issue was found by a custom fuzzer developed by Sechang Lim . 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(struct 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. -- 2.55.0