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rds: drop incoming messages that cross network namespace boundaries

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rds_find_bound() looks up the destination socket using a global
rhashtable keyed solely on (addr, port, scope_id).  Network namespaces
are not part of the key, so a sender in netns A can deliver an incoming
message (inc) to a socket that lives in a different netns B.

When this happens, inc->i_conn points to an rds_connection whose c_net
is netns A, but the receiving rs lives in netns B.  Once the child
process that created netns A exits, cleanup_net() calls
rds_loop_exit_net() -> rds_loop_kill_conns() -> rds_conn_destroy(),
freeing that connection.  If the survivor socket in netns B still holds
the inc, any subsequent dereference of inc->i_conn is a use-after-free.

There are two dangerous sites in rds_clear_recv_queue():
  1. inc->i_conn->c_lcong (offset 88 of freed rds_connection, size 200)
     read via rds_recv_rcvbuf_delta() -- confirmed by KASAN.
  2. inc->i_conn->c_trans->inc_free(inc) (function pointer at offset 80)
     called via rds_inc_put() when the inc refcount reaches zero -- same
     race window, potential call-through-freed-object primitive.

The bug is reachable from unprivileged user namespaces
(CLONE_NEWUSER + CLONE_NEWNET), available since Linux 3.8.

Fix this by rejecting the delivery in rds_recv_incoming() when the
socket returned by rds_find_bound() belongs to a different network
namespace than the connection that carried the message.  Use the
existing rds_conn_net() / sock_net() helpers and net_eq() for the
comparison.

Fixes: c809195f55 ("rds: clean up loopback rds_connections on netns deletion")
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
Reviewed-by: Allison Henderson <achender@kernel.org>
Tested-by: Allison Henderson <achender@kernel.org>
Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260708024314.601139-1-achender@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Aldo Ariel Panzardo 2026-07-07 19:43:14 -07:00 committed by Paolo Abeni
parent e32649b4ba
commit 5521ae71e3
1 changed files with 15 additions and 0 deletions
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15
net/rds/recv.c
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@ -399,6 +399,21 @@ void rds_recv_incoming(struct rds_connection *conn, struct in6_addr *saddr,
goto out;
}
/*
* rds_find_bound() uses a global (netns-agnostic) hash table.
* An RDS connection created in netns A can match a socket bound
* in the init netns, delivering inc cross-netns with inc->i_conn
* pointing into netns A. When cleanup_net() then frees that conn,
* any subsequent dereference of inc->i_conn is a use-after-free.
* Drop the inc if the receiving socket lives in a different netns.
*/
if (!net_eq(sock_net(rds_rs_to_sk(rs)), rds_conn_net(conn))) {
rds_stats_inc(s_recv_drop_no_sock);
rds_sock_put(rs);
rs = NULL;
goto out;
}
/* Process extension headers */
rds_recv_incoming_exthdrs(inc, rs);