niu: Fix kernel buffer overflow for ETHTOOL_GRXCLSRLALL

niu_get_ethtool_tcam_all() assumes that its output buffer is the right
size, and warns before returning if it is not.  However, the output
buffer size is under user control and ETHTOOL_GRXCLSRLALL is an
unprivileged ethtool command.  Therefore this is at least a local
denial-of-service vulnerability.

Change it to check before writing each entry and to return an error if
the buffer is already full.

Compile-tested only.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 10 deletions

diff --git a/drivers/net/niu.c b/drivers/net/niu.c
index b9b950845b0..340cbec4894 100644
--- a/drivers/net/niu.c
+++ b/drivers/net/niu.c
@@ -7272,32 +7272,28 @@ static int niu_get_ethtool_tcam_all(struct niu *np,
         struct niu_parent *parent = np->parent;
         struct niu_tcam_entry *tp;
         int i, idx, cnt;
-        u16 n_entries;
         unsigned long flags;
-
+        int ret = 0;
 
         /* put the tcam size here */
         nfc->data = tcam_get_size(np);
 
         niu_lock_parent(np, flags);
-        n_entries = nfc->rule_cnt;
         for (cnt = 0, i = 0; i < nfc->data; i++) {
                 idx = tcam_get_index(np, i);
                 tp = &parent->tcam[idx];
                 if (!tp->valid)
                         continue;
+                if (cnt == nfc->rule_cnt) {
+                        ret = -EMSGSIZE;
+                        break;
+                }
                 rule_locs[cnt] = i;
                 cnt++;
         }
         niu_unlock_parent(np, flags);
 
-        if (n_entries != cnt) {
-                /* print warning, this should not happen */
-                netdev_info(np->dev, "niu%d: In %s(): n_entries[%d] != cnt[%d]!!!\n",
-                            np->parent->index, __func__, n_entries, cnt);
-        }
-
-        return 0;
+        return ret;
 }
 
 static int niu_get_nfc(struct net_device *dev, struct ethtool_rxnfc *cmd,