Patch "af_unix: fix struct pid leaks in OOB support" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    af_unix: fix struct pid leaks in OOB support

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     af_unix-fix-struct-pid-leaks-in-oob-support.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7d3549e6637b492a96883eeafba75d3cabcfa571
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Tue Mar 7 16:45:30 2023 +0000

    af_unix: fix struct pid leaks in OOB support
    
    [ Upstream commit 2aab4b96900272885bc157f8b236abf1cdc02e08 ]
    
    syzbot reported struct pid leak [1].
    
    Issue is that queue_oob() calls maybe_add_creds() which potentially
    holds a reference on a pid.
    
    But skb->destructor is not set (either directly or by calling
    unix_scm_to_skb())
    
    This means that subsequent kfree_skb() or consume_skb() would leak
    this reference.
    
    In this fix, I chose to fully support scm even for the OOB message.
    
    [1]
    BUG: memory leak
    unreferenced object 0xffff8881053e7f80 (size 128):
    comm "syz-executor242", pid 5066, jiffies 4294946079 (age 13.220s)
    hex dump (first 32 bytes):
    01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
    backtrace:
    [<ffffffff812ae26a>] alloc_pid+0x6a/0x560 kernel/pid.c:180
    [<ffffffff812718df>] copy_process+0x169f/0x26c0 kernel/fork.c:2285
    [<ffffffff81272b37>] kernel_clone+0xf7/0x610 kernel/fork.c:2684
    [<ffffffff812730cc>] __do_sys_clone+0x7c/0xb0 kernel/fork.c:2825
    [<ffffffff849ad699>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff849ad699>] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84a0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
    
    Fixes: 314001f0bf92 ("af_unix: Add OOB support")
    Reported-by: syzbot+7699d9e5635c10253a27@xxxxxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Cc: Rao Shoaib <rao.shoaib@xxxxxxxxxx>
    Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230307164530.771896-1-edumazet@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 32ddf8fe32c69..a96026dbdf94e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1970,7 +1970,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 #define UNIX_SKB_FRAGS_SZ (PAGE_SIZE << get_order(32768))
 
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
-static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other)
+static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other,
+		     struct scm_cookie *scm, bool fds_sent)
 {
 	struct unix_sock *ousk = unix_sk(other);
 	struct sk_buff *skb;
@@ -1981,6 +1982,11 @@ static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other
 	if (!skb)
 		return err;
 
+	err = unix_scm_to_skb(scm, skb, !fds_sent);
+	if (err < 0) {
+		kfree_skb(skb);
+		return err;
+	}
 	skb_put(skb, 1);
 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);
 
@@ -2108,7 +2114,7 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
 	if (msg->msg_flags & MSG_OOB) {
-		err = queue_oob(sock, msg, other);
+		err = queue_oob(sock, msg, other, &scm, fds_sent);
 		if (err)
 			goto out_err;
 		sent++;