[PATCH net] RDS/IB: validate receive completion payload length

[PATCH net] RDS/IB: validate receive completion payload length

[sungbyeongchan]

An RDS/RDMA peer can declare a fragment length larger than the payload
reported by the receive completion. The receive path attaches the recycled
receive fragment without validating those lengths, allowing recvmsg() to
return stale bytes beyond the actual payload.

Validate data_len against the expected current-fragment length before
transferring fragment ownership. Disconnect and reconnect on mismatch.

The issue reproduced in two clean QEMU boots. A peer declared 4096 bytes
while posting only 16 bytes, and a receiver under a different UID obtained
4080-byte tails from prior messages in all 256 attempts in each boot. With
this change, the malformed message was not delivered, reconnection
succeeded, and a subsequent normal 4096-byte message was delivered intact.

Fixes: 1e23b3ee0e94 ("RDS/IB: Receive datagrams via IB")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: sungbyeongchan <tjdqudcks0424@naver.com>
---
 net/rds/ib_recv.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c
index bd6cb3ffaa571..0daddb108c8a7 100644
--- a/net/rds/ib_recv.c
+++ b/net/rds/ib_recv.c
@@ -949,6 +949,15 @@ static void rds_ib_process_recv(struct rds_connection *conn,
 		}
 	}
 
+	if (data_len != min_t(u32, ic->i_recv_data_rem, RDS_FRAG_SIZE)) {
+		rds_ib_conn_error(conn,
+				  "incoming fragment payload length %u, expected %u; "
+				  "disconnecting and reconnecting\n",
+				  data_len,
+				  min_t(u32, ic->i_recv_data_rem, RDS_FRAG_SIZE));
+		goto done;
+	}
+
 	list_add_tail(&recv->r_frag->f_item, &ibinc->ii_frags);
 	recv->r_frag = NULL;
 
-- 
2.43.0

Re: [PATCH net] RDS/IB: validate receive completion payload length

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net] RDS/IB: validate receive completion payload length

[Allison Henderson]

On Wed, 2026-10-07 at 05:52 +0900, sungbyeongchan wrote:
> An RDS/RDMA peer can declare a fragment length larger than the payload
> reported by the receive completion. The receive path attaches the recycled
> receive fragment without validating those lengths, allowing recvmsg() to
> return stale bytes beyond the actual payload.
> 
> Validate data_len against the expected current-fragment length before
> transferring fragment ownership. Disconnect and reconnect on mismatch.
> 
> The issue reproduced in two clean QEMU boots. A peer declared 4096 bytes
> while posting only 16 bytes, and a receiver under a different UID obtained
> 4080-byte tails from prior messages in all 256 attempts in each boot. With
> this change, the malformed message was not delivered, reconnection
> succeeded, and a subsequent normal 4096-byte message was delivered intact.
> 
> Fixes: 1e23b3ee0e94 ("RDS/IB: Receive datagrams via IB")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: sungbyeongchan <tjdqudcks0424@naver.com>

Hi Sungbyeongchan,

Thanks for sending this, and for following up on the earlier feedback so
quickly.  However, I realized after I sent it that another contributor had
already publicly sent an equivalent fix earlier today, and the convention is
to take the first correct patch on the list.
https://lore.kernel.org/netdev/20261006125720.81227-1-shubham@octane.security/

So no need to follow up with the sashiko review, and I apologize for the
miss-communication, but I will ask your Reported-by tag to be applied since you
were the first to report the same bug. This was a solid find, and the reproduction
was very well done. Please continue to send RDS fixes as you find them.

Thank you!
Allison

> ---
>  net/rds/ib_recv.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c
> index bd6cb3ffaa571..0daddb108c8a7 100644
> --- a/net/rds/ib_recv.c
> +++ b/net/rds/ib_recv.c
> @@ -949,6 +949,15 @@ static void rds_ib_process_recv(struct rds_connection *conn,
>  		}
>  	}
>  
> +	if (data_len != min_t(u32, ic->i_recv_data_rem, RDS_FRAG_SIZE)) {
> +		rds_ib_conn_error(conn,
> +				  "incoming fragment payload length %u, expected %u; "
> +				  "disconnecting and reconnecting\n",
> +				  data_len,
> +				  min_t(u32, ic->i_recv_data_rem, RDS_FRAG_SIZE));
> +		goto done;
> +	}
> +
>  	list_add_tail(&recv->r_frag->f_item, &ibinc->ii_frags);
>  	recv->r_frag = NULL;
>