af_unix: Don't call wait_for_unix_gc() on every sendmsg().

We have been calling wait_for_unix_gc() on every sendmsg() in case
there are too many inflight AF_UNIX sockets.

This is also because the old GC implementation had poor knowledge
of the inflight sockets and had to suspect every sendmsg().

This was improved by commit d9f21b361333 ("af_unix: Try to run GC
async."), but we do not even need to call wait_for_unix_gc() if the
process is not sending AF_UNIX sockets.

The wait_for_unix_gc() call only helps when a malicious process
continues to create cyclic references, and we can detect that
in a better place and slow it down.

Let's move wait_for_unix_gc() to unix_prepare_fpl() that is called
only when AF_UNIX socket fd is passed via SCM_RIGHTS.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251115020935.2643121-5-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 4a80dac56bbd99eebe7863cdb782ab07acafd45f..34952242bd81a988d41b79ca355d88f404ad61e9 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2098,8 +2098,6 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
        if (err < 0)
                return err;
 
-       wait_for_unix_gc(scm.fp);
-
        if (msg->msg_flags & MSG_OOB) {
                err = -EOPNOTSUPP;
                goto out;
@@ -2393,8 +2391,6 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
        if (err < 0)
                return err;
 
-       wait_for_unix_gc(scm.fp);
-
        if (msg->msg_flags & MSG_OOB) {
                err = -EOPNOTSUPP;
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)

diff --git a/net/unix/af_unix.h b/net/unix/af_unix.h
index 0fb5b348ad9444594909cef2319596b0203d2046..2f1bfe3217c1a6585995c46edb0732b89f9c2308 100644 (file)
--- a/net/unix/af_unix.h
+++ b/net/unix/af_unix.h
@@ -30,7 +30,6 @@ void unix_update_edges(struct unix_sock *receiver);
 int unix_prepare_fpl(struct scm_fp_list *fpl);
 void unix_destroy_fpl(struct scm_fp_list *fpl);
 void unix_schedule_gc(void);
-void wait_for_unix_gc(struct scm_fp_list *fpl);
 
 /* SOCK_DIAG */
 long unix_inq_len(struct sock *sk);

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 190dea73f0abad0f9903e3771b9cb26d57dd2d68..280b9b07b1c0fc5e1f968a58887ed7c1c8113c02 100644 (file)
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -282,6 +282,8 @@ void unix_update_edges(struct unix_sock *receiver)
        }
 }
 
+static void wait_for_unix_gc(struct scm_fp_list *fpl);
+
 int unix_prepare_fpl(struct scm_fp_list *fpl)
 {
        struct unix_vertex *vertex;
@@ -303,6 +305,8 @@ int unix_prepare_fpl(struct scm_fp_list *fpl)
        if (!fpl->edges)
                goto err;
 
+       wait_for_unix_gc(fpl);
+
        return 0;
 
 err:
@@ -628,7 +632,7 @@ void unix_schedule_gc(void)
 #define UNIX_INFLIGHT_TRIGGER_GC 16000
 #define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)
 
-void wait_for_unix_gc(struct scm_fp_list *fpl)
+static void wait_for_unix_gc(struct scm_fp_list *fpl)
 {
        /* If number of inflight sockets is insane,
         * force a garbage collect right now.
@@ -642,8 +646,7 @@ void wait_for_unix_gc(struct scm_fp_list *fpl)
        /* Penalise users who want to send AF_UNIX sockets
         * but whose sockets have not been received yet.
         */
-       if (!fpl || !fpl->count_unix ||
-           READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
+       if (READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
                return;
 
        if (READ_ONCE(gc_in_progress))