linux-kernel - [PATCH] Fix compat_sys_sigpending breakage introduced by v4.13-rc1~6^2~12

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Date:   Sat, 5 Aug 2017 23:00:50 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        Anatoly Pugachev <matorola@...il.com>,
        Eugene Syromyatnikov <evgsyr@...il.com>
Subject: [PATCH] Fix compat_sys_sigpending breakage introduced by
 v4.13-rc1~6^2~12

The latest change of compat_sys_sigpending has broken it in two ways.

First, it tries to write 4 bytes more than userspace expects:
sizeof(old_sigset_t) == sizeof(long) == 8 instead of
sizeof(compat_old_sigset_t) == sizeof(u32) == 4.

Second, on big endian architectures these bytes are being written
in the wrong order.

This bug was found by strace test suite.

Reported-by: Anatoly Pugachev <matorola@...il.com>
Inspired-by: Eugene Syromyatnikov <evgsyr@...il.com>
Fixes: 8f13621abced ("sigpending(): move compat to native")
Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
---
 kernel/signal.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index caed913..7e33f8c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3303,12 +3303,15 @@ SYSCALL_DEFINE1(sigpending, old_sigset_t __user *, set)
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE1(sigpending, compat_old_sigset_t __user *, set32)
 {
+#ifdef __BIG_ENDIAN
 	sigset_t set;
-	int err = do_sigpending(&set, sizeof(old_sigset_t)); 
-	if (err == 0)
-		if (copy_to_user(set32, &set, sizeof(old_sigset_t)))
-			err = -EFAULT;
+	int err = do_sigpending(&set, sizeof(set.sig[0]));
+	if (!err)
+		err = put_user(set.sig[0], set32);
 	return err;
+#else
+	return sys_rt_sigpending((sigset_t __user *)set32, sizeof(*set32));
+#endif
 }
 #endif
 
-- 
ldv