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

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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 d9f21b3613 ("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>
This commit is contained in:
Kuniyuki Iwashima
2025-11-15 02:08:35 +00:00
committed by Jakub Kicinski
parent da8fc7a39b
commit 384900542d
3 changed files with 6 additions and 8 deletions
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4
net/unix/af_unix.c
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@@ -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)