[PATCH 3.2 060/153] s390: fix handling of -1 in set{,fs}[gu]id16 syscalls

[Ben Hutchings]

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eugene Syromiatnikov <esyr@xxxxxxxxxx>

commit 6dd0d2d22aa363fec075cb2577ba273ac8462e94 upstream.

For some reason, the implementation of some 16-bit ID system calls
(namely, setuid16/setgid16 and setfsuid16/setfsgid16) used type cast
instead of low2highgid/low2highuid macros for converting [GU]IDs, which
led to incorrect handling of value of -1 (which ought to be considered
invalid).

Discovered by strace test suite.

Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/s390/kernel/compat_linux.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/arch/s390/kernel/compat_linux.c
+++ b/arch/s390/kernel/compat_linux.c
@@ -114,7 +114,7 @@ asmlinkage long sys32_setregid16(u16 rgi
 
 asmlinkage long sys32_setgid16(u16 gid)
 {
-	return sys_setgid((gid_t)gid);
+	return sys_setgid(low2highgid(gid));
 }
 
 asmlinkage long sys32_setreuid16(u16 ruid, u16 euid)
@@ -124,7 +124,7 @@ asmlinkage long sys32_setreuid16(u16 rui
 
 asmlinkage long sys32_setuid16(u16 uid)
 {
-	return sys_setuid((uid_t)uid);
+	return sys_setuid(low2highuid(uid));
 }
 
 asmlinkage long sys32_setresuid16(u16 ruid, u16 euid, u16 suid)
@@ -163,12 +163,12 @@ asmlinkage long sys32_getresgid16(u16 __
 
 asmlinkage long sys32_setfsuid16(u16 uid)
 {
-	return sys_setfsuid((uid_t)uid);
+	return sys_setfsuid(low2highuid(uid));
 }
 
 asmlinkage long sys32_setfsgid16(u16 gid)
 {
-	return sys_setfsgid((gid_t)gid);
+	return sys_setfsgid(low2highgid(gid));
 }
 
 static int groups16_to_user(u16 __user *grouplist, struct group_info *group_info)