From: Sidraya Jayagond Date: Mon, 3 Aug 2026 07:07:01 +0000 (+0200) Subject: net/smc: fix TOCTOU race between smc_listen_out() and listener close X-Git-Url: http://git.ipfire.org/index.cgi?a=commitdiff_plain;h=185a4caeecabc150106deda1da170b09f2ad803f;p=thirdparty%2Fkernel%2Flinux.git net/smc: fix TOCTOU race between smc_listen_out() and listener close smc_listen_out() reads lsmc->sk.sk_state without the listener lock, then acquires lock_sock_nested() only after the check passes. This opens a window where smc_close_active() can transition the listener to SMC_CLOSED, call smc_close_cleanup_listen() to drain the accept queue, and release the lock, all between the lockless read and the delayed lock acquisition: smc_listen_work (smc_hs_wq) smc_close_active() ------------------------------- ------------------------- release_sock(child) if (sk_state == SMC_LISTEN) TRUE lock_sock(listener) sk_state = SMC_CLOSED smc_close_cleanup_listen() release_sock(listener) flush_work(tcp_listen_work) lock_sock_nested(listener) smc_accept_enqueue(listener, child) /* child enqueued on dead listener */ smc_close_active() flushes only tcp_listen_work. Work items already dispatched onto smc_hs_wq for the CLC handshake continue running unguarded. smc_accept_enqueue() takes a sock_hold() on the child that is never released, so the child smc_sock, its clcsock, and the reference all leak. A remote peer that opens TCP connections while the server calls close() can exhaust kernel memory. Move lock_sock_nested() to before the sk_state check so that the test and the enqueue are atomic under the listener lock. Fixes: fd57770dd198 ("net/smc: wait for pending work before clcsock release_sock") Reviewed-by: Mahanta Jambigi Signed-off-by: Sidraya Jayagond Reviewed-by: Breno Leitao Reviewed-by: Dust Li Link: https://patch.msgid.link/20260803070701.126339-1-sidraya@linux.ibm.com Signed-off-by: Paolo Abeni --- diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index b5db69073e20..00403175b740 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -1931,11 +1931,12 @@ static void smc_listen_out(struct smc_sock *new_smc) atomic_dec(&lsmc->queued_smc_hs); release_sock(newsmcsk); /* lock in smc_listen_work() */ + lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING); if (lsmc->sk.sk_state == SMC_LISTEN) { - lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING); smc_accept_enqueue(&lsmc->sk, newsmcsk); release_sock(&lsmc->sk); } else { /* no longer listening */ + release_sock(&lsmc->sk); smc_close_non_accepted(newsmcsk); }