[LTP] [PATCH v3] syscalls/prctl04: Fix false positive report when SECCOMP_MODE_FILTER is not supported

[He Zhe]

The child process really should not receive the expected siganl, SIGSYS, when
kernel doesn't support SECCOMP_MODE_FILTER.

This patch tests if SECCOMP_MODE_FILTER is supported in setup and adds a
variable to record it.

Before this patch:
root@xilinx-zynq:~# /opt/ltp/testcases/bin/prctl04
tst_test.c:1431: TINFO: Timeout per run is 0h 05m 00s
---- snip ----
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:204: TFAIL: SECCOMP_MODE_FILTER permits exit() unexpectedly
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER

After this patch:
root@xilinx-zynq:~# /opt/ltp/testcases/bin/prctl04
tst_test.c:1431: TINFO: Timeout per run is 0h 05m 00s
---- snip ----
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER
prctl04.c:154: TCONF: kernel doesn't support SECCOMP_MODE_FILTER

Signed-off-by: He Zhe <zhe.he@windriver.com>
---
v2: Add a variable to record the support status instead of exit(1)
v3: Move mode_filter_not_supported check a bit upper to save a prctl call

 testcases/kernel/syscalls/prctl/prctl04.c | 30 +++++++++++++++++------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/testcases/kernel/syscalls/prctl/prctl04.c b/testcases/kernel/syscalls/prctl/prctl04.c
index b9f4c2a10..d3de4b0d6 100644
--- a/testcases/kernel/syscalls/prctl/prctl04.c
+++ b/testcases/kernel/syscalls/prctl/prctl04.c
@@ -93,6 +93,9 @@ static struct tcase {
 	"SECCOMP_MODE_FILTER doesn't permit exit()"}
 };
 
+
+static int mode_filter_not_supported;
+
 static void check_filter_mode_inherit(void)
 {
 	int childpid;
@@ -154,16 +157,17 @@ static void check_filter_mode(int val)
 {
 	int fd;
 
+	if (mode_filter_not_supported == 1) {
+		tst_res(TCONF, "kernel doesn't support SECCOMP_MODE_FILTER");
+		return;
+	}
+
 	fd = SAFE_OPEN(FNAME, O_RDWR | O_CREAT, 0666);
 
 	TEST(prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &strict));
 	if (TST_RET == -1) {
-		if (TST_ERR == EINVAL)
-			tst_res(TCONF,
-				"kernel doesn't support SECCOMP_MODE_FILTER");
-		else
-			tst_res(TFAIL | TERRNO,
-				"prctl(PR_SET_SECCOMP) sets SECCOMP_MODE_FILTER failed");
+		tst_res(TFAIL | TERRNO,
+			"prctl(PR_SET_SECCOMP) sets SECCOMP_MODE_FILTER failed");
 		return;
 	}
 
@@ -208,7 +212,7 @@ static void verify_prctl(unsigned int n)
 			return;
 		}
 
-		if (tc->pass_flag == 2)
+		if (mode_filter_not_supported == 0 && tc->pass_flag == 2)
 			tst_res(TFAIL,
 				"SECCOMP_MODE_FILTER permits exit() unexpectedly");
 	}
@@ -218,7 +222,17 @@ static void setup(void)
 {
 	TEST(prctl(PR_GET_SECCOMP));
 	if (TST_RET == 0) {
-		tst_res(TINFO, "kernel support PR_GET/SET_SECCOMP");
+		tst_res(TINFO, "kernel supports PR_GET/SET_SECCOMP");
+
+		TEST(prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, NULL));
+		if (TST_RET == -1)
+			if (TST_ERR == EINVAL) {
+				mode_filter_not_supported = 1;
+				return;
+			}
+
+		tst_res(TINFO, "kernel supports SECCOMP_MODE_FILTER");
+
 		return;
 	}
 
-- 
2.25.1