irda: prevent integer underflow in IRLMP_ENUMDEVICES

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@vsecurity.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/irda/af_irda.c b/net/irda/af_irda.c
index 7f09798..5007541 100644 (file)
--- a/net/irda/af_irda.c
+++ b/net/irda/af_irda.c
@@ -2281,6 +2281,16 @@ 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) {
+                       err = -EINVAL;
+                       goto out;
+               }
+
                /* Ask lmp for the current discovery log */
                discoveries = irlmp_get_discoveries(&list.len, self->mask.word,
                                                    self->nslots);
@@ -2291,15 +2301,9 @@ static int irda_getsockopt(struct socket *sock, int level, int optname,
                }
 
                /* 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) {
                        err = -EINVAL;