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Wed, 11 Nov 2026 14:51:55 -0800 (PST) Received: from sid-dev-env.cgrhrlrrq2nuffriizdlnb1x4b.xx.internal.cloudapp.net ([4.155.54.158]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8baaa86dd0fsm2471575b3a.22.2026.11.11.14.51.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 14:51:54 -0800 (PST) From: Siddharth Chintamaneni To: Kuniyuki Iwashima , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Shuah Khan , Kirill Tkhai , apais@microsoft.com, hargar@linux.microsoft.com, rlmenge@gmail.com, egoriluk@gmail.com, netdev@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Siddharth Chintamaneni Subject: [PATCH net v2 1/2] af_unix: Fix scm_stat.nr_fds leak in unix_dgram_disconnected(). Date: Wed, 11 Nov 2026 22:51:47 +0000 Message-ID: <20261111225148.88506-2-sidchintamaneni@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261111225148.88506-1-sidchintamaneni@gmail.com> References: <20261111225148.88506-1-sidchintamaneni@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When a connected SOCK_DGRAM socket disconnects (e.g. via connect() with AF_UNSPEC), reconnects to a different peer, or observes a dead peer in unix_dgram_sendmsg(), unix_dgram_disconnected() purges all unread datagrams from sk->sk_receive_queue via skb_queue_purge_reason(). Because skb_queue_purge_reason() frees each skb without calling scm_stat_del(sk, skb), any SCM_RIGHTS file descriptors attached to the purged skbs remain permanently accounted in u->scm_stat.nr_fds (reported as scm_fds in /proc//fdinfo/) for the remaining lifetime of the socket. Move scm_stat_add() and scm_stat_del() above unix_dgram_disconnected(), splice sk->sk_receive_queue onto a local list under the queue lock, and call scm_stat_del() before kfree_skb_reason() on each purged skb. Fixes: 3c32da19a858 ("unix: Show number of pending scm files of receive queue in fdinfo") Signed-off-by: Siddharth Chintamaneni --- net/unix/af_unix.c | 59 +++++++++++++++++++++++++++------------------- 1 file changed, 35 insertions(+), 24 deletions(-) diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 98fcfd7301f6..990a98330d9c 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -609,6 +609,28 @@ static void unix_write_space(struct sock *sk) rcu_read_unlock(); } +static void scm_stat_add(struct sock *sk, struct sk_buff *skb) +{ + struct scm_fp_list *fp = UNIXCB(skb).fp; + struct unix_sock *u = unix_sk(sk); + + if (unlikely(fp && fp->count)) { + atomic_add(fp->count, &u->scm_stat.nr_fds); + unix_add_edges(fp, u); + } +} + +static void scm_stat_del(struct sock *sk, struct sk_buff *skb) +{ + struct scm_fp_list *fp = UNIXCB(skb).fp; + struct unix_sock *u = unix_sk(sk); + + if (unlikely(fp && fp->count)) { + atomic_sub(fp->count, &u->scm_stat.nr_fds); + unix_del_edges(fp); + } +} + /* When dgram socket disconnects (or changes its peer), we clear its receive * queue of packets arrived from previous peer. First, it allows to do * flow control based only on wmem_alloc; second, sk connected to peer @@ -616,8 +638,19 @@ static void unix_write_space(struct sock *sk) static void unix_dgram_disconnected(struct sock *sk, struct sock *other) { if (!skb_queue_empty(&sk->sk_receive_queue)) { - skb_queue_purge_reason(&sk->sk_receive_queue, - SKB_DROP_REASON_UNIX_DISCONNECT); + struct sk_buff_head tmp; + struct sk_buff *skb; + + __skb_queue_head_init(&tmp); + + spin_lock(&sk->sk_receive_queue.lock); + skb_queue_splice_init(&sk->sk_receive_queue, &tmp); + spin_unlock(&sk->sk_receive_queue.lock); + + while ((skb = __skb_dequeue(&tmp)) != NULL) { + scm_stat_del(sk, skb); + kfree_skb_reason(skb, SKB_DROP_REASON_UNIX_DISCONNECT); + } wake_up_interruptible_all(&unix_sk(sk)->peer_wait); @@ -2058,28 +2091,6 @@ static bool unix_skb_scm_eq(const struct sock *sk, struct sk_buff *skb, unix_secdata_eq(scm, skb); } -static void scm_stat_add(struct sock *sk, struct sk_buff *skb) -{ - struct scm_fp_list *fp = UNIXCB(skb).fp; - struct unix_sock *u = unix_sk(sk); - - if (unlikely(fp && fp->count)) { - atomic_add(fp->count, &u->scm_stat.nr_fds); - unix_add_edges(fp, u); - } -} - -static void scm_stat_del(struct sock *sk, struct sk_buff *skb) -{ - struct scm_fp_list *fp = UNIXCB(skb).fp; - struct unix_sock *u = unix_sk(sk); - - if (unlikely(fp && fp->count)) { - atomic_sub(fp->count, &u->scm_stat.nr_fds); - unix_del_edges(fp); - } -} - static void unix_orphan_scm(struct sock *sk, struct sk_buff *skb) { scm_stat_del(sk, skb); -- 2.43.0