ppp: clarify parsing of user supplied data in ppp_set_compress()

* Split big conditional statement.
  * Check (data.length <= CCP_MAX_OPTION_LENGTH) only once.
  * Don't read ccp_option[1] if not initialised.

Reading uninitialised ccp_option[1] was harmless, because this could
only happen when data.length was 0 or 1. So even then, we couldn't pass
the (ccp_option[1] < 2 || ccp_option[1] > data.length) test anyway.

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index fc8ad00..04f4eb3 100644 (file)
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -2429,13 +2429,15 @@ ppp_set_compress(struct ppp *ppp, unsigned long arg)
        unsigned char ccp_option[CCP_MAX_OPTION_LENGTH];
 
        err = -EFAULT;
-       if (copy_from_user(&data, (void __user *) arg, sizeof(data)) ||
-           (data.length <= CCP_MAX_OPTION_LENGTH &&
-            copy_from_user(ccp_option, (void __user *) data.ptr, data.length)))
+       if (copy_from_user(&data, (void __user *) arg, sizeof(data)))
                goto out;
+       if (data.length > CCP_MAX_OPTION_LENGTH)
+               goto out;
+       if (copy_from_user(ccp_option, (void __user *) data.ptr, data.length))
+               goto out;
+
        err = -EINVAL;
-       if (data.length > CCP_MAX_OPTION_LENGTH ||
-           ccp_option[1] < 2 || ccp_option[1] > data.length)
+       if (data.length < 2 || ccp_option[1] < 2 || ccp_option[1] > data.length)
                goto out;
 
        cp = try_then_request_module(