linux-kernel - [tip: core/entry] selftests: Fix errno checking in syscall_user

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Message-ID: <174983307279.406.8576482002031316721.tip-bot2@tip-bot2>
Date: Fri, 13 Jun 2025 16:44:32 -0000
From: "tip-bot2 for Dmitry Vyukov" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Dmitry Vyukov <dvyukov@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: core/entry] selftests: Fix errno checking in syscall_user_dispatch test

The following commit has been merged into the core/entry branch of tip:

Commit-ID:     b89732c8c8357487185f260a723a060b3476144e
Gitweb:        https://git.kernel.org/tip/b89732c8c8357487185f260a723a060b3476144e
Author:        Dmitry Vyukov <dvyukov@...gle.com>
AuthorDate:    Wed, 21 May 2025 17:04:28 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 13 Jun 2025 18:36:39 +02:00

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.

Fixes: 179ef035992e ("selftests: Add kselftest for syscall user dispatch")
Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/af6a04dbfef9af8570f5bab43e3ef1416b62699a.1747839857.git.dvyukov@google.com


---
 tools/testing/selftests/syscall_user_dispatch/sud_test.c | 50 +++----
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/tools/testing/selftests/syscall_user_dispatch/sud_test.c b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
index d975a67..48cf01a 100644
--- a/tools/testing/selftests/syscall_user_dispatch/sud_test.c
+++ b/tools/testing/selftests/syscall_user_dispatch/sud_test.c
@@ -79,6 +79,21 @@ TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
 	}
 }
 
+static void prctl_valid(struct __test_metadata *_metadata,
+			unsigned long op, unsigned long off,
+			unsigned long size, void *sel)
+{
+	EXPECT_EQ(0, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, off, size, sel));
+}
+
+static void prctl_invalid(struct __test_metadata *_metadata,
+			  unsigned long op, unsigned long off,
+			  unsigned long size, void *sel, int err)
+{
+	EXPECT_EQ(-1, prctl(PR_SET_SYSCALL_USER_DISPATCH, op, off, size, sel));
+	EXPECT_EQ(err, errno);
+}
+
 TEST(bad_prctl_param)
 {
 	char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
@@ -86,57 +101,42 @@ TEST(bad_prctl_param)
 
 	/* Invalid op */
 	op = -1;
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel);
-	ASSERT_EQ(EINVAL, errno);
+	prctl_invalid(_metadata, op, 0, 0, &sel, EINVAL);
 
 	/* PR_SYS_DISPATCH_OFF */
 	op = PR_SYS_DISPATCH_OFF;
 
 	/* offset != 0 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0);
-	EXPECT_EQ(EINVAL, errno);
+	prctl_invalid(_metadata, op, 0x1, 0x0, 0, EINVAL);
 
 	/* len != 0 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
-	EXPECT_EQ(EINVAL, errno);
+	prctl_invalid(_metadata, op, 0x0, 0xff, 0, EINVAL);
 
 	/* sel != NULL */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
-	EXPECT_EQ(EINVAL, errno);
+	prctl_invalid(_metadata, op, 0x0, 0x0, &sel, EINVAL);
 
 	/* Valid parameter */
-	errno = 0;
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0);
-	EXPECT_EQ(0, errno);
+	prctl_valid(_metadata, 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(EINVAL, errno);
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel);
-	EXPECT_EQ(EINVAL, errno);
+	prctl_invalid(_metadata, op, 0x1, 0x0, &sel, EINVAL);
+	prctl_invalid(_metadata, op, -1L, 0x0, &sel, EINVAL);
 
 	/* Invalid selector */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1);
-	ASSERT_EQ(EFAULT, errno);
+	prctl_invalid(_metadata, op, 0x0, 0x1, (void *) -1, EFAULT);
 
 	/*
 	 * Dispatcher range overflows unsigned long
 	 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel);
-	ASSERT_EQ(EINVAL, errno) {
-		TH_LOG("Should reject bad syscall range");
-	}
+	prctl_invalid(_metadata, PR_SYS_DISPATCH_ON, 1, -1L, &sel, EINVAL);
 
 	/*
 	 * Allowed range overflows usigned long
 	 */
-	prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel);
-	ASSERT_EQ(EINVAL, errno) {
-		TH_LOG("Should reject bad syscall range");
-	}
+	prctl_invalid(_metadata, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel, EINVAL);
 }
 
 /*