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[68.48.65.54]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8d30570c305sm77413366d6.48.2026.06.14.06.07.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Jun 2026 06:07:28 -0700 (PDT) From: Michael Bommarito To: Allison Henderson , "David S . Miller" , Jakub Kicinski , Paolo Abeni , Eric Dumazet Cc: Simon Horman , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org Subject: [PATCH net] net: rds: check cmsg_len before reading rds_rdma_args in size pass Date: Sun, 14 Jun 2026 09:07:25 -0400 Message-ID: <20260614130725.2520842-1-michael.bommarito@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit For RDS_CMSG_RDMA_ARGS, rds_rm_size() calls rds_rdma_extra_size() after only CMSG_OK(), without checking that cmsg_len covers struct rds_rdma_args. rds_rdma_extra_size() reads args->local_vec_addr and args->nr_local, so a short control message reads past the copied control buffer. The value bounds an allocation count, so this is an out-of-bounds read in the kernel, not a leak to user space, and an unprivileged AF_RDS socket can trigger it with one short cmsg. The two later RDS_RDMA passes (rds_cmsg_rdma_args() and the rdma-bytes loop in rds_sendmsg()) already reject cmsg_len < CMSG_LEN(sizeof(struct rds_rdma_args)); only this size pass does not. Reject it the same way. Reproduced under KASAN on QEMU via a KUnit driving the real rds_rm_size(); the out-of-bounds read is gone after this change. Fixes: ff87e97a9d70 ("RDS: make m_rdma_op a member of rds_message") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito --- A short RDS_CMSG_RDMA_ARGS placed at a page boundary makes rds_rdma_extra_size() read the args fields past the allocation: BUG: KASAN: slab-out-of-bounds in rds_rdma_extra_size an 8-byte read. On stock it faults; patched it returns -EINVAL with no report. Controls (well-formed args; a short cmsg with args still in bounds) drive the same pass cleanly on both trees. No in-tree selftest exercises rds_rm_size(); I can send the KUnit suite as a separate net-next patch if wanted, kept out so the fix is not held. net/rds/send.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/rds/send.c b/net/rds/send.c index d8b14ff9d366b..6ca3192b1d8af 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -967,6 +967,8 @@ static int rds_rm_size(struct msghdr *msg, int num_sgs, switch (cmsg->cmsg_type) { case RDS_CMSG_RDMA_ARGS: + if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct rds_rdma_args))) + return -EINVAL; if (vct->indx >= vct->len) { vct->len += vct->incr; tmp_iov = base-commit: 5200f5f493f79f14bbdc349e402a40dfb32f23c8 -- 2.53.0