[PATCH 1/1] af_unix: Fix memory leak in unix_dgram_sendmsg()

[PATCH 1/1] af_unix: Fix memory leak in unix_dgram_sendmsg()

[Adrian Huang]

From: Adrian Huang <ahuang12@lenovo.com>

After running the 'sendmsg02' program of Linux Test Project (LTP),
kmemleak reports the following memory leak:

  # cat /sys/kernel/debug/kmemleak
  unreferenced object 0xffff888243866800 (size 2048):
    comm "sendmsg02", pid 67, jiffies 4294903166
    hex dump (first 32 bytes):
      00 00 00 00 00 00 00 00 5e 00 00 00 00 00 00 00  ........^.......
      01 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00  ...@............
    backtrace (crc 7e96a3f2):
      kmemleak_alloc+0x56/0x90
      kmem_cache_alloc_noprof+0x209/0x450
      sk_prot_alloc.constprop.0+0x60/0x160
      sk_alloc+0x32/0xc0
      unix_create1+0x67/0x2b0
      unix_create+0x47/0xa0
      __sock_create+0x12e/0x200
      __sys_socket+0x6d/0x100
      __x64_sys_socket+0x1b/0x30
      x64_sys_call+0x7e1/0x2140
      do_syscall_64+0x54/0x110
      entry_SYSCALL_64_after_hwframe+0x76/0x7e

Commit 689c398885cc ("af_unix: Defer sock_put() to clean up path in
unix_dgram_sendmsg().") defers sock_put() in the error handling path.
However, it fails to account for the condition 'msg->msg_namelen != 0',
resulting in a memory leak when the code jumps to the 'lookup' label.

Fix issue by calling sock_put() if 'msg->msg_namelen != 0' is met.

Fixes: 689c398885cc ("af_unix: Defer sock_put() to clean up path in unix_dgram_sendmsg().")
Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
---
 net/unix/af_unix.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 34945de1fb1f..cf37a1f92831 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2100,6 +2100,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 		if (!msg->msg_namelen) {
 			err = -ECONNRESET;
 			goto out_sock_put;
+		} else {
+			sock_put(other);
 		}
 
 		goto lookup;
-- 
2.34.1

Re: [PATCH 1/1] af_unix: Fix memory leak in unix_dgram_sendmsg()

[Kuniyuki Iwashima]

From: Adrian Huang <adrianhuang0701@gmail.com>
Date: Mon, 24 Feb 2025 23:28:46 +0800
> From: Adrian Huang <ahuang12@lenovo.com>
> 
> After running the 'sendmsg02' program of Linux Test Project (LTP),
> kmemleak reports the following memory leak:
> 
>   # cat /sys/kernel/debug/kmemleak
>   unreferenced object 0xffff888243866800 (size 2048):
>     comm "sendmsg02", pid 67, jiffies 4294903166
>     hex dump (first 32 bytes):
>       00 00 00 00 00 00 00 00 5e 00 00 00 00 00 00 00  ........^.......
>       01 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00  ...@............
>     backtrace (crc 7e96a3f2):
>       kmemleak_alloc+0x56/0x90
>       kmem_cache_alloc_noprof+0x209/0x450
>       sk_prot_alloc.constprop.0+0x60/0x160
>       sk_alloc+0x32/0xc0
>       unix_create1+0x67/0x2b0
>       unix_create+0x47/0xa0
>       __sock_create+0x12e/0x200
>       __sys_socket+0x6d/0x100
>       __x64_sys_socket+0x1b/0x30
>       x64_sys_call+0x7e1/0x2140
>       do_syscall_64+0x54/0x110
>       entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 
> Commit 689c398885cc ("af_unix: Defer sock_put() to clean up path in
> unix_dgram_sendmsg().") defers sock_put() in the error handling path.
> However, it fails to account for the condition 'msg->msg_namelen != 0',
> resulting in a memory leak when the code jumps to the 'lookup' label.
> 
> Fix issue by calling sock_put() if 'msg->msg_namelen != 0' is met.
> 
> Fixes: 689c398885cc ("af_unix: Defer sock_put() to clean up path in unix_dgram_sendmsg().")
> Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
> ---
>  net/unix/af_unix.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 34945de1fb1f..cf37a1f92831 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2100,6 +2100,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  		if (!msg->msg_namelen) {
>  			err = -ECONNRESET;
>  			goto out_sock_put;
> +		} else {
> +			sock_put(other);
>  		}
>  
>  		goto lookup;

nit: else is not needed:

	if (!msg->msg_namelen) {
		err = -ECONNRESET;
		goto out_sock_put;
	}

	sock_put(other);
	goto lookup;

Thanks!