[PATCH net v2] rds: fix out-of-bounds conn_path walks via handshake exthdrs

[Henry Martin <bsdhenrymartin@gmail.com>]

Both the lane and the connection-generation negotiation are driven by
extension headers in handshake packets, and both are processed
unconditionally, even on transports that are not multipath capable.
A non-MP connection (t_mp_capable unset) owns exactly one
rds_conn_path slot, so a peer claiming up to RDS_MPATH_WORKERS lanes
makes every subsequent fan-out walk conn->c_path[0..7] at 504-byte
strides past the single allocated slot (KASAN: "Read of size 8 in
rds_conn_path_connect_if_down"); the generation negotiation opens a
similar out-of-bounds walk on the same array.

Only process handshake extension headers when the connection's
transport is multipath capable, so a peer can never make us walk
lanes that do not exist.  Both call sites in rds_recv_incoming() are
gated.

This is a port of the Oracle UEK fix for the same issue, picked up
where Paula's series of the same change left off.

This issue was discovered by Tencent CodeBuddy Security.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/netdev/20260825120132.51636-1-pamoutafpro@gmail.com/
Link: https://github.com/oracle/linux-uek/commit/2fdeb0513f18
Fixes: 840df162b3eb ("rds: reduce memory footprint for RDS when transport is RDMA")
Fixes: 905dd4184e07 ("RDS: TCP: Track peer's connection generation number")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
---

v2: Replace the two allocation-bound clamps with a port of the UEK
    t_mp_capable handshake gating (suggested by Allison Henderson),
    correct the Fixes tags and link Paula's series.

 net/rds/recv.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/rds/recv.c b/net/rds/recv.c
index 6204e577a90ae..93ee4546ae362 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -379,7 +379,8 @@ void rds_recv_incoming(struct rds_connection *conn, struct in6_addr *saddr,
 		rds_stats_inc(s_recv_ping);
 		rds_send_pong(cp, inc->i_hdr.h_sport);
 		/* if this is a handshake ping, start multipath if necessary */
-		if (RDS_HS_PROBE(be16_to_cpu(inc->i_hdr.h_sport),
+		if (conn->c_trans->t_mp_capable &&
+		    RDS_HS_PROBE(be16_to_cpu(inc->i_hdr.h_sport),
 				 be16_to_cpu(inc->i_hdr.h_dport))) {
 			rds_recv_hs_exthdrs(&inc->i_hdr, cp->cp_conn);
 			rds_start_mprds(cp->cp_conn);
@@ -387,7 +388,8 @@ void rds_recv_incoming(struct rds_connection *conn, struct in6_addr *saddr,
 		goto out;
 	}
 
-	if (be16_to_cpu(inc->i_hdr.h_dport) ==  RDS_FLAG_PROBE_PORT &&
+	if (conn->c_trans->t_mp_capable &&
+	    be16_to_cpu(inc->i_hdr.h_dport) ==  RDS_FLAG_PROBE_PORT &&
 	    inc->i_hdr.h_sport == 0) {
 		rds_recv_hs_exthdrs(&inc->i_hdr, cp->cp_conn);
 		/* if this is a handshake pong, start multipath if necessary */
-- 
2.43.7