[34-longterm 236/247] irda: prevent integer underflow in IRLMP_ENUMDEVICES

[Paul Gortmaker]

From: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit fdac1e0697356ac212259f2147aa60c72e334861 upstream.

If the user-provided len is less than the expected offset, the
IRLMP_ENUMDEVICES getsockopt will do a copy_to_user() with a very large
size value.  While this isn't be a security issue on x86 because it will
get caught by the access_ok() check, it may leak large amounts of kernel
heap on other architectures.  In any event, this patch fixes it.

Signed-off-by: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 net/irda/af_irda.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/irda/af_irda.c b/net/irda/af_irda.c
index 6fae047..e63c226 100644
--- a/net/irda/af_irda.c
+++ b/net/irda/af_irda.c
@@ -2278,6 +2278,14 @@ static int __irda_getsockopt(struct socket *sock, int level, int optname,
 
 	switch (optname) {
 	case IRLMP_ENUMDEVICES:
+
+		/* Offset to first device entry */
+		offset = sizeof(struct irda_device_list) -
+			sizeof(struct irda_device_info);
+
+		if (len < offset)
+			return -EINVAL;
+
 		/* Ask lmp for the current discovery log */
 		discoveries = irlmp_get_discoveries(&list.len, self->mask.word,
 						    self->nslots);
@@ -2287,15 +2295,9 @@ static int __irda_getsockopt(struct socket *sock, int level, int optname,
 		err = 0;
 
 		/* Write total list length back to client */
-		if (copy_to_user(optval, &list,
-				 sizeof(struct irda_device_list) -
-				 sizeof(struct irda_device_info)))
+		if (copy_to_user(optval, &list, offset))
 			err = -EFAULT;
 
-		/* Offset to first device entry */
-		offset = sizeof(struct irda_device_list) -
-			sizeof(struct irda_device_info);
-
 		/* Copy the list itself - watch for overflow */
 		if(list.len > 2048)
 		{
-- 
1.7.4.4

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