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>

drivers/isdn/i4l/isdn_ppp.c

@@ -322,9 +322,9 @@ isdn_ppp_open(int min, struct file *file)
 	 * VJ header compression init
 	 */
 	is->slcomp = slhc_init(16, 16);	/* not necessary for 2. link in bundle */
-	if (!is->slcomp) {
+	if (IS_ERR(is->slcomp)) {
 		isdn_ppp_ccp_reset_free(is);
-		return -ENOMEM;
+		return PTR_ERR(is->slcomp);
 	}
 #endif
 #ifdef CONFIG_IPPP_FILTER
@@ -573,10 +573,8 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
 			is->maxcid = val;
 #ifdef CONFIG_ISDN_PPP_VJ
 			sltmp = slhc_init(16, val);
-			if (!sltmp) {
-				printk(KERN_ERR "ippp, can't realloc slhc struct\n");
-				return -ENOMEM;
-			}
+			if (IS_ERR(sltmp))
+				return PTR_ERR(sltmp);
 			if (is->slcomp)
 				slhc_free(is->slcomp);
 			is->slcomp = sltmp;

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);

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)
@@ -94,19 +95,22 @@ 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)
 			goto out_free;
 		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 @@ slhc_init(int rslots, int tslots)
 out_free:
 	kfree(comp);
 out_fail:
-	return NULL;
+	return ERR_PTR(-ENOMEM);
 }
 
 

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);