ppp, slip: Validate VJ compression slot parameters completely

Currently slhc_init() treats out-of-range values of rslots and tslots
as equivalent to 0, except that if tslots is too large it will
dereference a null pointer (CVE-2015-7799).

Add a range-check at the top of the function and make it return an
ERR_PTR() on error instead of NULL.  Change the callers accordingly.

Compile-tested only.

Reported-by: 郭永刚 <guoyonggang@360.cn>
References: http://article.gmane.org/gmane.comp.security.oss.general/17908
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 11 insertions, 9 deletions

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index ed00446759b2..9a863c6a6a33 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -721,10 +721,8 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			val &= 0xffff;
 		}
 		vj = slhc_init(val2+1, val+1);
-		if (!vj) {
-			netdev_err(ppp->dev,
-				   "PPP: no memory (VJ compressor)\n");
-			err = -ENOMEM;
+		if (IS_ERR(vj)) {
+			err = PTR_ERR(vj);
 			break;
 		}
 		ppp_lock(ppp);
diff --git a/drivers/net/slip/slhc.c b/drivers/net/slip/slhc.c
index 079f7adfcde5..27ed25252aac 100644
--- a/drivers/net/slip/slhc.c
+++ b/drivers/net/slip/slhc.c
@@ -84,8 +84,9 @@ static long decode(unsigned char **cpp);
 static unsigned char * put16(unsigned char *cp, unsigned short x);
 static unsigned short pull16(unsigned char **cpp);
 
-/* Initialize compression data structure
+/* Allocate compression data structure
  *	slots must be in range 0 to 255 (zero meaning no compression)
+ * Returns pointer to structure or ERR_PTR() on error.
  */
 struct slcompress *
 slhc_init(int rslots, int tslots)
@@ -94,11 +95,14 @@ slhc_init(int rslots, int tslots)
 	register struct cstate *ts;
 	struct slcompress *comp;
 
+	if (rslots < 0 || rslots > 255 || tslots < 0 || tslots > 255)
+		return ERR_PTR(-EINVAL);
+
 	comp = kzalloc(sizeof(struct slcompress), GFP_KERNEL);
 	if (! comp)
 		goto out_fail;
 
-	if ( rslots > 0  &&  rslots < 256 ) {
+	if (rslots > 0) {
 		size_t rsize = rslots * sizeof(struct cstate);
 		comp->rstate = kzalloc(rsize, GFP_KERNEL);
 		if (! comp->rstate)
@@ -106,7 +110,7 @@ slhc_init(int rslots, int tslots)
 		comp->rslot_limit = rslots - 1;
 	}
 
-	if ( tslots > 0  &&  tslots < 256 ) {
+	if (tslots > 0) {
 		size_t tsize = tslots * sizeof(struct cstate);
 		comp->tstate = kzalloc(tsize, GFP_KERNEL);
 		if (! comp->tstate)
@@ -141,7 +145,7 @@ out_free2:
 out_free:
 	kfree(comp);
 out_fail:
-	return NULL;
+	return ERR_PTR(-ENOMEM);
 }
 
 
diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index 05387b1e2e95..a17d86a57734 100644
--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c
@@ -164,7 +164,7 @@ static int sl_alloc_bufs(struct slip *sl, int mtu)
 	if (cbuff == NULL)
 		goto err_exit;
 	slcomp = slhc_init(16, 16);
-	if (slcomp == NULL)
+	if (IS_ERR(slcomp))
 		goto err_exit;
 #endif
 	spin_lock_bh(&sl->lock);