linux-kernel - [PATCH] s390: fix setgid16/setuid16 handling of -1

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Date:   Mon, 15 Jan 2018 12:52:42 +0100
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     linux-s390@...r.kernel.org
Cc:     Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] s390: fix setgid16/setuid16 handling of -1

For some reason, the implementation of these two 16-bit ID system calls
used cast instead of low2highgid/low2highuid macros for converting [GU]IDs,
which leads to incorrect handling of value of -1 (which ought to be
considered invalid).

Discovered by strace test suite.

Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
---
 arch/s390/kernel/compat_linux.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
index f04db37..e48a31a 100644
--- a/arch/s390/kernel/compat_linux.c
+++ b/arch/s390/kernel/compat_linux.c
@@ -110,7 +110,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setregid16, u16, rgid, u16, egid)
 
 COMPAT_SYSCALL_DEFINE1(s390_setgid16, u16, gid)
 {
-	return sys_setgid((gid_t)gid);
+	return sys_setgid(low2highgid(gid));
 }
 
 COMPAT_SYSCALL_DEFINE2(s390_setreuid16, u16, ruid, u16, euid)
@@ -120,7 +120,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setreuid16, u16, ruid, u16, euid)
 
 COMPAT_SYSCALL_DEFINE1(s390_setuid16, u16, uid)
 {
-	return sys_setuid((uid_t)uid);
+	return sys_setuid(low2highuid(uid));
 }
 
 COMPAT_SYSCALL_DEFINE3(s390_setresuid16, u16, ruid, u16, euid, u16, suid)
-- 
2.9.3