[PATCH] getgroups16() fix

sys_getgroups16 (or rather groups16_to_user()) returns large gids
truncated.  Needs to be fixed, one way or another.  Don't know why the
other similar casts are still there.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/sched.h

@@ -364,6 +364,12 @@ struct group_info {
 	gid_t *blocks[0];
 };
 
+/*
+ * get_group_info() must be called with the owning task locked (via task_lock())
+ * when task != current.  The reason being that the vast majority of callers are
+ * looking at current->group_info, which can not be changed except by the
+ * current task.  Changing current->group_info requires the task lock, too.
+ */
 #define get_group_info(group_info) do { \
 	atomic_inc(&(group_info)->usage); \
 } while (0)
@@ -930,7 +936,9 @@ static inline int thread_group_empty(task_t *p)
 extern void unhash_process(struct task_struct *p);
 
 /*
- * Protects ->fs, ->files, ->mm, ->ptrace and synchronises with wait4().
+ * Protects ->fs, ->files, ->mm, ->ptrace, ->group_info and synchronises with
+ * wait4().
+ *
  * Nests both inside and outside of read_lock(&tasklist_lock).
  * It must not be nested with write_lock_irq(&tasklist_lock),
  * neither inside nor outside.

kernel/uid16.c

@@ -39,7 +39,7 @@ asmlinkage long sys_setregid16(old_gid_t rgid, old_gid_t egid)
 
 asmlinkage long sys_setgid16(old_gid_t gid)
 {
-	return sys_setgid((gid_t)gid);
+	return sys_setgid(low2highgid(gid));
 }
 
 asmlinkage long sys_setreuid16(old_uid_t ruid, old_uid_t euid)
@@ -49,7 +49,7 @@ asmlinkage long sys_setreuid16(old_uid_t ruid, old_uid_t euid)
 
 asmlinkage long sys_setuid16(old_uid_t uid)
 {
-	return sys_setuid((uid_t)uid);
+	return sys_setuid(low2highuid(uid));
 }
 
 asmlinkage long sys_setresuid16(old_uid_t ruid, old_uid_t euid, old_uid_t suid)
@@ -88,12 +88,12 @@ asmlinkage long sys_getresgid16(old_gid_t __user *rgid, old_gid_t __user *egid,
 
 asmlinkage long sys_setfsuid16(old_uid_t uid)
 {
-	return sys_setfsuid((uid_t)uid);
+	return sys_setfsuid(low2highuid(uid));
 }
 
 asmlinkage long sys_setfsgid16(old_gid_t gid)
 {
-	return sys_setfsgid((gid_t)gid);
+	return sys_setfsgid(low2highgid(gid));
 }
 
 static int groups16_to_user(old_gid_t __user *grouplist,
@@ -103,7 +103,7 @@ static int groups16_to_user(old_gid_t __user *grouplist,
 	old_gid_t group;
 
 	for (i = 0; i < group_info->ngroups; i++) {
-		group = (old_gid_t)GROUP_AT(group_info, i);
+		group = high2lowgid(GROUP_AT(group_info, i));
 		if (put_user(group, grouplist+i))
 			return -EFAULT;
 	}
@@ -120,7 +120,7 @@ static int groups16_from_user(struct group_info *group_info,
 	for (i = 0; i < group_info->ngroups; i++) {
 		if (get_user(group, grouplist+i))
 			return  -EFAULT;
-		GROUP_AT(group_info, i) = (gid_t)group;
+		GROUP_AT(group_info, i) = low2highgid(group);
 	}
 
 	return 0;