[PATCH 4.9 10/47] af_key: fix buffer overread in parse_exthdrs()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 4e765b4972af7b07adcb1feb16e7a525ce1f6b28 upstream.

If a message sent to a PF_KEY socket ended with an incomplete extension
header (fewer than 4 bytes remaining), then parse_exthdrs() read past
the end of the message, into uninitialized memory.  Fix it by returning
-EINVAL in this case.

Reproducer:

	#include <linux/pfkeyv2.h>
	#include <sys/socket.h>
	#include <unistd.h>

	int main()
	{
		int sock = socket(PF_KEY, SOCK_RAW, PF_KEY_V2);
		char buf[17] = { 0 };
		struct sadb_msg *msg = (void *)buf;

		msg->sadb_msg_version = PF_KEY_V2;
		msg->sadb_msg_type = SADB_DELETE;
		msg->sadb_msg_len = 2;

		write(sock, buf, 17);
	}

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/key/af_key.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -516,6 +516,9 @@ static int parse_exthdrs(struct sk_buff
 		uint16_t ext_type;
 		int ext_len;
 
+		if (len < sizeof(*ehdr))
+			return -EINVAL;
+
 		ext_len  = ehdr->sadb_ext_len;
 		ext_len *= sizeof(uint64_t);
 		ext_type = ehdr->sadb_ext_type;