linux-kernel - [PATCH v2 2/3] selftests: Fix errno checking in syscall_user

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Message-ID: <d11d91e0c27ef78affcef06e00d1cf4cd8747fcc.1740386567.git.dvyukov@google.com>
Date: Mon, 24 Feb 2025 09:45:26 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: krisman@...labora.com, tglx@...utronix.de, luto@...nel.org, 
	peterz@...radead.org, keescook@...omium.org, gregory.price@...verge.com
Cc: Dmitry Vyukov <dvyukov@...gle.com>, Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] selftests: Fix errno checking in syscall_user_dispatch test

Successful syscalls don't change errno, so checking errno is wrong
to ensure that a syscall has failed. For example for the following
sequence:

	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
	EXPECT_EQ(EINVAL, errno);
	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
	EXPECT_EQ(EINVAL, errno);

only the first syscall may fail and set errno, but the second may succeed
and keep errno intact, and the check will falsely pass.
Or if errno happened to be EINVAL before, even the first check may falsely
pass.

Also use EXPECT/ASSERT consistently. Currently there is an inconsistent mix
without obvious reasons for usage of one or another.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Gabriel Krisman Bertazi <krisman@...labora.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Gregory Price <gregory.price@...verge.com>
Cc: Marco Elver <elver@...gle.com>
Cc: linux-kernel@...r.kernel.org
---
 .../syscall_user_dispatch/sud_test.c          | 30 +++++++++----------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/syscall_user_dispatch/sud_test.c b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
index d975a67673299..b0969925ec64c 100644
--- a/tools/testing/selftests/syscall_user_dispatch/sud_test.c
+++ b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
@@ -86,55 +86,53 @@ TEST(bad_prctl_param)
 
 	/* Invalid op */
 	op = -1;
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel);
-	ASSERT_EQ(EINVAL, errno);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel));
+	EXPECT_EQ(EINVAL, errno);
 
 	/* PR_SYS_DISPATCH_OFF */
 	op = PR_SYS_DISPATCH_OFF;
 
 	/* offset != 0 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0));
 	EXPECT_EQ(EINVAL, errno);
 
 	/* len != 0 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0));
 	EXPECT_EQ(EINVAL, errno);
 
 	/* sel != NULL */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel));
 	EXPECT_EQ(EINVAL, errno);
 
 	/* Valid parameter */
-	errno = 0;
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0);
-	EXPECT_EQ(0, errno);
+	EXPECT_EQ(0, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0));
 
 	/* PR_SYS_DISPATCH_ON */
 	op = PR_SYS_DISPATCH_ON;
 
 	/* Dispatcher region is bad (offset > 0 && len == 0) */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, &sel);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, &sel));
 	EXPECT_EQ(EINVAL, errno);
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel));
 	EXPECT_EQ(EINVAL, errno);
 
 	/* Invalid selector */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1);
-	ASSERT_EQ(EFAULT, errno);
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1));
+	EXPECT_EQ(EFAULT, errno);
 
 	/*
 	 * Dispatcher range overflows unsigned long
 	 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel);
-	ASSERT_EQ(EINVAL, errno) {
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel));
+	EXPECT_EQ(EINVAL, errno) {
 		TH_LOG("Should reject bad syscall range");
 	}
 
 	/*
 	 * Allowed range overflows usigned long
 	 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel);
-	ASSERT_EQ(EINVAL, errno) {
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel));
+	EXPECT_EQ(EINVAL, errno) {
 		TH_LOG("Should reject bad syscall range");
 	}
 }
-- 
2.48.1.601.g30ceb7b040-goog