[PATCH net] af_unix: fix struct pid leaks in OOB support

[PATCH net] af_unix: fix struct pid leaks in OOB support

[Eric Dumazet]

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@syzkaller.appspotmail.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Rao Shoaib <rao.shoaib@oracle.com>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/unix/af_unix.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 347122c3575eaae597405369e2e9d8324d6ad240..0b0f18ecce4470d6fd21c084a3ea49e04dcbb9bd 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2105,7 +2105,8 @@ 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;
@@ -2116,6 +2117,11 @@ 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);
 
@@ -2243,7 +2249,7 @@ 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++;
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

Re: [PATCH net] af_unix: fix struct pid leaks in OOB support

[Kuniyuki Iwashima]

From:   Eric Dumazet <edumazet@google.com>
Date:   Tue,  7 Mar 2023 16:45:30 +0000
> 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@syzkaller.appspotmail.com
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thanks!


> Cc: Rao Shoaib <rao.shoaib@oracle.com>
> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  net/unix/af_unix.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 347122c3575eaae597405369e2e9d8324d6ad240..0b0f18ecce4470d6fd21c084a3ea49e04dcbb9bd 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2105,7 +2105,8 @@ 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;
> @@ -2116,6 +2117,11 @@ 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);
>  
> @@ -2243,7 +2249,7 @@ 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++;
> -- 
> 2.40.0.rc0.216.gc4246ad0f0-goog

Re: [PATCH net] af_unix: fix struct pid leaks in OOB support

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  7 Mar 2023 16:45:30 +0000 you wrote:
> 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())
> 
> [...]

Here is the summary with links:
  - [net] af_unix: fix struct pid leaks in OOB support
    https://git.kernel.org/netdev/net/c/2aab4b969002

You are awesome, thank you!
-- 
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