linux-kernel - [PATCH v2] fs/signalfd.c: Fix inconsistent return codes for signalfd4

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Date:   Sat, 30 May 2020 12:07:07 +0200
From:   Helge Deller <deller@....de>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Laurent Vivier <laurent@...ier.eu>
Subject: [PATCH v2] fs/signalfd.c: Fix inconsistent return codes for signalfd4

The kernel signalfd4() syscall returns different error codes when called
either in compat or native mode. This behaviour makes correct emulation in qemu
and testing programs like LTP more complicated.

Fix the code to always return -in both modes- EFAULT for unaccessible user
memory, and EINVAL when called with an invalid signal mask.

Signed-off-by: Helge Deller <deller@....de>

---
Changelog v2:
- Rephrased commit message.

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 44b6845b071c..5b78719be445 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -314,9 +314,10 @@ SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
 {
 	sigset_t mask;

-	if (sizemask != sizeof(sigset_t) ||
-	    copy_from_user(&mask, user_mask, sizeof(mask)))
+	if (sizemask != sizeof(sigset_t))
 		return -EINVAL;
+	if (copy_from_user(&mask, user_mask, sizeof(mask)))
+		return -EFAULT;
 	return do_signalfd4(ufd, &mask, flags);
 }

@@ -325,9 +326,10 @@ SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
 {
 	sigset_t mask;

-	if (sizemask != sizeof(sigset_t) ||
-	    copy_from_user(&mask, user_mask, sizeof(mask)))
+	if (sizemask != sizeof(sigset_t))
 		return -EINVAL;
+	if (copy_from_user(&mask, user_mask, sizeof(mask)))
+		return -EFAULT;
 	return do_signalfd4(ufd, &mask, 0);
 }