netdev - Re: What is lock_sock() before skb_free

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Message-Id: <200904191412.GIF95380.SVFJOHOFOQtLMF@I-love.SAKURA.ne.jp>
Date:	Sun, 19 Apr 2009 14:12:15 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: What is lock_sock() before skb_free_datagram() for?

David Miller wrote:
> We worked so hard to split out this common code, it is simply
> a non-starter for anyone to start putting protocol specific test
> into here, or even worse to move this code back to being locally
> copied into every protocol implementation.
You don't want LSM modules to perform protocol specific test inside
__skb_recv_datagram(). I see.

> You may want to think about how you can achieve your goals by putting
> these unpleasant hooks into some other location.
May I insert security_socket_post_recv_datagram() into the caller of
skb_recv_datagram() (as shown below)?

 include/linux/security.h |   39 +++++++++++++++++++++++++++++++++++++++
 net/ipv4/raw.c           |    5 +++++
 net/ipv4/udp.c           |    7 +++++++
 net/ipv6/raw.c           |    5 +++++
 net/ipv6/udp.c           |    7 +++++++
 net/socket.c             |    5 +++++
 security/capability.c    |   13 +++++++++++++
 security/security.c      |   11 +++++++++++
 8 files changed, 92 insertions(+)

--- security-testing-2.6.git.orig/net/ipv4/raw.c
+++ security-testing-2.6.git/net/ipv4/raw.c
@@ -666,6 +666,11 @@ static int raw_recvmsg(struct kiocb *ioc
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb)
 		goto out;
+	err = security_socket_post_recv_datagram(sk, skb, flags);
+	if (err) {
+		skb_kill_datagram(sk, skb, flags);
+		goto out;
+	}
 
 	copied = skb->len;
 	if (len < copied) {
--- security-testing-2.6.git.orig/net/ipv4/udp.c
+++ security-testing-2.6.git/net/ipv4/udp.c
@@ -901,6 +901,13 @@ try_again:
 				  &peeked, &err);
 	if (!skb)
 		goto out;
+	err = security_socket_post_recv_datagram(sk, skb, flags);
+	if (err) {
+		lock_sock(sk);
+		skb_kill_datagram(sk, skb, flags);
+		release_sock(sk);
+		goto out;
+	}
 
 	ulen = skb->len - sizeof(struct udphdr);
 	copied = len;
--- security-testing-2.6.git.orig/net/ipv6/raw.c
+++ security-testing-2.6.git/net/ipv6/raw.c
@@ -465,6 +465,11 @@ static int rawv6_recvmsg(struct kiocb *i
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb)
 		goto out;
+	err = security_socket_post_recv_datagram(sk, skb, flags);
+	if (err) {
+		skb_kill_datagram(sk, skb, flags);
+		goto out;
+	}
 
 	copied = skb->len;
 	if (copied > len) {
--- security-testing-2.6.git.orig/net/ipv6/udp.c
+++ security-testing-2.6.git/net/ipv6/udp.c
@@ -208,6 +208,13 @@ try_again:
 				  &peeked, &err);
 	if (!skb)
 		goto out;
+	err = security_socket_post_recv_datagram(sk, skb, flags);
+	if (err) {
+		lock_sock(sk);
+		skb_kill_datagram(sk, skb, flags);
+		release_sock(sk);
+		goto out;
+	}
 
 	ulen = skb->len - sizeof(struct udphdr);
 	copied = len;
--
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