NFC: llcp: integer underflow in nfc_llcp_set_remote_gb()

If gb_len is less than 3 it would cause an integer underflow and
possibly memory corruption in nfc_llcp_parse_gb_tlv().

I removed the old test for gb_len == 0.  I also removed the test for
->remote_gb == NULL.  It's not possible for ->remote_gb to be NULL and
we have already dereferenced ->remote_gb_len so it's too late to test.

The old test return -ENODEV but my test returns -EINVAL.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/net/nfc/llcp/llcp.c b/net/nfc/llcp/llcp.c
index 85bc75c38dea..746f5a2f9804 100644
--- a/net/nfc/llcp/llcp.c
+++ b/net/nfc/llcp/llcp.c
@@ -549,14 +549,13 @@ int nfc_llcp_set_remote_gb(struct nfc_dev *dev, u8 *gb, u8 gb_len)
                 pr_err("No LLCP device\n");
                 return -ENODEV;
         }
+        if (gb_len < 3)
+                return -EINVAL;
 
         memset(local->remote_gb, 0, NFC_MAX_GT_LEN);
         memcpy(local->remote_gb, gb, gb_len);
         local->remote_gb_len = gb_len;
 
-        if (local->remote_gb == NULL || local->remote_gb_len == 0)
-                return -ENODEV;
-
         if (memcmp(local->remote_gb, llcp_magic, 3)) {
                 pr_err("MAC does not support LLCP\n");
                 return -EINVAL;