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>

4 files changed, 15 insertions, 15 deletions

diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
index 86f9abebcb72..9c1e8adaf4fc 100644
--- a/drivers/isdn/i4l/isdn_ppp.c
+++ b/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;
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);