[PATCH 1/4] [PATCH] net: Limit socket I/O iovec total length to INT_MAX - CVE-2010-3859

[paolo.pisati at canonical.com]

From: Paolo Pisati <paolo.pisati at canonical.com>

BugLink: http://bugs.launchpad.net/bugs/708839

commit 8acfe468b0384e834a303f08ebc4953d72fb690a upstream.

This helps protect us from overflow issues down in the
individual protocol sendmsg/recvmsg handlers.  Once
we hit INT_MAX we truncate out the rest of the iovec
by setting the iov_len members to zero.

This works because:

1) For SOCK_STREAM and SOCK_SEQPACKET sockets, partial
   writes are allowed and the application will just continue
   with another write to send the rest of the data.

2) For datagram oriented sockets, where there must be a
   one-to-one correspondance between write() calls and
   packets on the wire, INT_MAX is going to be far larger
   than the packet size limit the protocol is going to
   check for and signal with -EMSGSIZE.

Based upon a patch by Linus Torvalds.

CVE-2010-3859

Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
Signed-off-by: Brad Figg <brad.figg at canonical.com>

Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 net/compat.c     |   10 ++++++----
 net/core/iovec.c |   15 +++++++--------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/net/compat.c b/net/compat.c
index 8d73905..2a2659b 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -40,10 +40,12 @@ static inline int iov_from_user_compat_to_kern(struct iovec *kiov,
 		compat_size_t len;
 
 		if (get_user(len, &uiov32->iov_len) ||
-		   get_user(buf, &uiov32->iov_base)) {
-			tot_len = -EFAULT;
-			break;
-		}
+		    get_user(buf, &uiov32->iov_base))
+			return -EFAULT;
+
+		if (len > INT_MAX - tot_len)
+			len = INT_MAX - tot_len;
+
 		tot_len += len;
 		kiov->iov_base = compat_ptr(buf);
 		kiov->iov_len = (__kernel_size_t) len;
diff --git a/net/core/iovec.c b/net/core/iovec.c
index 16ad45d..b6a4780 100644
--- a/net/core/iovec.c
+++ b/net/core/iovec.c
@@ -60,14 +60,13 @@ int verify_iovec(struct msghdr *m, struct iovec *iov, struct sockaddr *address,
 	err = 0;
 
 	for (ct = 0; ct < m->msg_iovlen; ct++) {
-		err += iov[ct].iov_len;
-		/*
-		 * Goal is not to verify user data, but to prevent returning
-		 * negative value, which is interpreted as errno.
-		 * Overflow is still possible, but it is harmless.
-		 */
-		if (err < 0)
-			return -EMSGSIZE;
+		size_t len = iov[ct].iov_len;
+
+		if (len > INT_MAX - err) {
+			len = INT_MAX - err;
+			iov[ct].iov_len = len;
+		}
+		err += len;
 	}
 
 	return err;
-- 
1.7.4.1