dccp: allow probing of CCID-array length

This fixes a problem in the DCCP getsockopt() API: currently there is no way
for a user to a priori know the number of built-in CCIDs, other than trying
DCCP_SOCKOPT_AVAILABLE_CCIDS in a loop, incrementing the option length until
EINVAL is no longer returned.

This patch truncates the array to the user-provided length. No copy is made
when the length is <= 0.

Due to the length restriction in do_dccp_getsockopt() to sizeof(int), the
minimum array length remains 4, which is a reasonable default (only 3
CCIDs, CCID-2..4, are currently defined).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 5 deletions

diff --git a/net/dccp/ccid.c b/net/dccp/ccid.c
index ff16e9df1969..49d27c556bec 100644
--- a/net/dccp/ccid.c
+++ b/net/dccp/ccid.c
@@ -63,14 +63,13 @@ int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
         u8 *ccid_array, array_len;
         int err = 0;
 
-        if (len < ARRAY_SIZE(ccids))
-                return -EINVAL;
-
         if (ccid_get_builtin_ccids(&ccid_array, &array_len))
                 return -ENOBUFS;
 
-        if (put_user(array_len, optlen) ||
-            copy_to_user(optval, ccid_array, array_len))
+        if (put_user(array_len, optlen))
+                err = -EFAULT;
+        else if (len > 0 && copy_to_user(optval, ccid_array,
+                                         len > array_len ? array_len : len))
                 err = -EFAULT;
 
         kfree(ccid_array);