[PATCH] sys_set_mempolicy() doesnt check if mode < 0

A kernel BUG() is triggered by a call to set_mempolicy() with a negative
first argument.  This is because the mode is declared as an int, and the
validity check doesnt check < 0 values.  Alternatively, mode could be
declared as unsigned int or unsigned long.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/mempolicy.c

@@ -443,7 +443,7 @@ asmlinkage long sys_set_mempolicy(int mode, unsigned long __user *nmask,
 	struct mempolicy *new;
 	DECLARE_BITMAP(nodes, MAX_NUMNODES);
 
-	if (mode > MPOL_MAX)
+	if (mode < 0 || mode > MPOL_MAX)
 		return -EINVAL;
 	err = get_nodes(nodes, nmask, maxnode, mode);
 	if (err)