kernel/groups.c: fix integer overflow in groups_search

gid_t is a unsigned int.  If group_info contains a gid greater than
MAX_INT, groups_search() function may look on the wrong side of the search
tree.

This solves some unfair "permission denied" problems.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/groups.c b/kernel/groups.c
index 53b1916c9492..253dc0f35cf4 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -143,10 +143,9 @@ int groups_search(const struct group_info *group_info, gid_t grp)
         right = group_info->ngroups;
         while (left < right) {
                 unsigned int mid = (left+right)/2;
-                int cmp = grp - GROUP_AT(group_info, mid);
-                if (cmp > 0)
+                if (grp > GROUP_AT(group_info, mid))
                         left = mid + 1;
-                else if (cmp < 0)
+                else if (grp < GROUP_AT(group_info, mid))
                         right = mid;
                 else
                         return 1;