[PATCH AUTOSEL 5.10 10/23] pidfd: fix test failure due to stack overflow on some arches

[PATCH AUTOSEL 5.10 10/23] pidfd: fix test failure due to stack overflow on some arches

[Sasha Levin]

From: Axel Rasmussen <axelrasmussen@google.com>

[ Upstream commit 4cbd93c3c110447adc66cb67c08af21f939ae2d7 ]

When running the pidfd_fdinfo_test on arm64, it fails for me. After some
digging, the reason is that the child exits due to SIGBUS, because it
overflows the 1024 byte stack we've reserved for it.

To fix the issue, increase the stack size to 8192 bytes (this number is
somewhat arbitrary, and was arrived at through experimentation -- I kept
doubling until the failure no longer occurred).

Also, let's make the issue easier to debug. wait_for_pid() returns an
ambiguous value: it may return -1 in all of these cases:

1. waitpid() itself returned -1
2. waitpid() returned success, but we found !WIFEXITED(status).
3. The child process exited, but it did so with a -1 exit code.

There's no way for the caller to tell the difference. So, at least log
which occurred, so the test runner can debug things.

While debugging this, I found that we had !WIFEXITED(), because the
child exited due to a signal. This seems like a reasonably common case,
so also print out whether or not we have WIFSIGNALED(), and the
associated WTERMSIG() (if any). This lets us see the SIGBUS I'm fixing
clearly when it occurs.

Finally, I'm suspicious of allocating the child's stack on our stack.
man clone(2) suggests that the correct way to do this is with mmap(),
and in particular by setting MAP_STACK. So, switch to doing it that way
instead.

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/testing/selftests/pidfd/pidfd.h         | 13 ++++++++---
 .../selftests/pidfd/pidfd_fdinfo_test.c       | 22 +++++++++++++++----
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 01f8d3c0cf2cb..6922d6417e1cf 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -68,7 +68,7 @@
 #define PIDFD_SKIP 3
 #define PIDFD_XFAIL 4
 
-int wait_for_pid(pid_t pid)
+static inline int wait_for_pid(pid_t pid)
 {
 	int status, ret;
 
@@ -78,13 +78,20 @@ int wait_for_pid(pid_t pid)
 		if (errno == EINTR)
 			goto again;
 
+		ksft_print_msg("waitpid returned -1, errno=%d\n", errno);
 		return -1;
 	}
 
-	if (!WIFEXITED(status))
+	if (!WIFEXITED(status)) {
+		ksft_print_msg(
+		       "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n",
+		       WIFSIGNALED(status), WTERMSIG(status));
 		return -1;
+	}
 
-	return WEXITSTATUS(status);
+	ret = WEXITSTATUS(status);
+	ksft_print_msg("waitpid WEXITSTATUS=%d\n", ret);
+	return ret;
 }
 
 static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
index 22558524f71c3..3fd8e903118f5 100644
--- a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
@@ -12,6 +12,7 @@
 #include <string.h>
 #include <syscall.h>
 #include <sys/wait.h>
+#include <sys/mman.h>
 
 #include "pidfd.h"
 #include "../kselftest.h"
@@ -80,7 +81,10 @@ static inline int error_check(struct error *err, const char *test_name)
 	return err->code;
 }
 
+#define CHILD_STACK_SIZE 8192
+
 struct child {
+	char *stack;
 	pid_t pid;
 	int   fd;
 };
@@ -89,17 +93,22 @@ static struct child clone_newns(int (*fn)(void *), void *args,
 				struct error *err)
 {
 	static int flags = CLONE_PIDFD | CLONE_NEWPID | CLONE_NEWNS | SIGCHLD;
-	size_t stack_size = 1024;
-	char *stack[1024] = { 0 };
 	struct child ret;
 
 	if (!(flags & CLONE_NEWUSER) && geteuid() != 0)
 		flags |= CLONE_NEWUSER;
 
+	ret.stack = mmap(NULL, CHILD_STACK_SIZE, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+	if (ret.stack == MAP_FAILED) {
+		error_set(err, -1, "mmap of stack failed (errno %d)", errno);
+		return ret;
+	}
+
 #ifdef __ia64__
-	ret.pid = __clone2(fn, stack, stack_size, flags, args, &ret.fd);
+	ret.pid = __clone2(fn, ret.stack, CHILD_STACK_SIZE, flags, args, &ret.fd);
 #else
-	ret.pid = clone(fn, stack + stack_size, flags, args, &ret.fd);
+	ret.pid = clone(fn, ret.stack + CHILD_STACK_SIZE, flags, args, &ret.fd);
 #endif
 
 	if (ret.pid < 0) {
@@ -129,6 +138,11 @@ static inline int child_join(struct child *child, struct error *err)
 	else if (r > 0)
 		error_set(err, r, "child %d reported: %d", child->pid, r);
 
+	if (munmap(child->stack, CHILD_STACK_SIZE)) {
+		error_set(err, -1, "munmap of child stack failed (errno %d)", errno);
+		r = -1;
+	}
+
 	return r;
 }
 
-- 
2.34.1

[PATCH AUTOSEL 5.10 11/23] selftests: fixup build warnings in pidfd / clone3 tests

[Sasha Levin]

From: Axel Rasmussen <axelrasmussen@google.com>

[ Upstream commit e2aa5e650b07693477dff554053605976789fd68 ]

These are some trivial fixups, which were needed to build the tests with
clang and -Werror. The following issues are fixed:

- Remove various unused variables.
- In child_poll_leader_exit_test, clang isn't smart enough to realize
  syscall(SYS_exit, 0) won't return, so it complains we never return
  from a non-void function. Add an extra exit(0) to appease it.
- In test_pidfd_poll_leader_exit, ret may be branched on despite being
  uninitialized, if we have !use_waitpid. Initialize it to zero to get
  the right behavior in that case.

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/testing/selftests/clone3/clone3.c    | 2 --
 tools/testing/selftests/pidfd/pidfd_test.c | 6 +++---
 tools/testing/selftests/pidfd/pidfd_wait.c | 5 ++---
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index 076cf4325f783..cd4582129c7d6 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -126,8 +126,6 @@ static void test_clone3(uint64_t flags, size_t size, int expected,
 
 int main(int argc, char *argv[])
 {
-	pid_t pid;
-
 	uid_t uid = getuid();
 
 	ksft_print_header();
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
index 529eb700ac26a..9a2d64901d591 100644
--- a/tools/testing/selftests/pidfd/pidfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -441,7 +441,6 @@ static void test_pidfd_poll_exec(int use_waitpid)
 {
 	int pid, pidfd = 0;
 	int status, ret;
-	pthread_t t1;
 	time_t prog_start = time(NULL);
 	const char *test_name = "pidfd_poll check for premature notification on child thread exec";
 
@@ -500,13 +499,14 @@ static int child_poll_leader_exit_test(void *args)
 	 */
 	*child_exit_secs = time(NULL);
 	syscall(SYS_exit, 0);
+	/* Never reached, but appeases compiler thinking we should return. */
+	exit(0);
 }
 
 static void test_pidfd_poll_leader_exit(int use_waitpid)
 {
 	int pid, pidfd = 0;
-	int status, ret;
-	time_t prog_start = time(NULL);
+	int status, ret = 0;
 	const char *test_name = "pidfd_poll check for premature notification on non-empty"
 				"group leader exit";
 
diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c
index be2943f072f60..17999e082aa71 100644
--- a/tools/testing/selftests/pidfd/pidfd_wait.c
+++ b/tools/testing/selftests/pidfd/pidfd_wait.c
@@ -39,7 +39,7 @@ static int sys_waitid(int which, pid_t pid, siginfo_t *info, int options,
 
 TEST(wait_simple)
 {
-	int pidfd = -1, status = 0;
+	int pidfd = -1;
 	pid_t parent_tid = -1;
 	struct clone_args args = {
 		.parent_tid = ptr_to_u64(&parent_tid),
@@ -47,7 +47,6 @@ TEST(wait_simple)
 		.flags = CLONE_PIDFD | CLONE_PARENT_SETTID,
 		.exit_signal = SIGCHLD,
 	};
-	int ret;
 	pid_t pid;
 	siginfo_t info = {
 		.si_signo = 0,
@@ -88,7 +87,7 @@ TEST(wait_simple)
 
 TEST(wait_states)
 {
-	int pidfd = -1, status = 0;
+	int pidfd = -1;
 	pid_t parent_tid = -1;
 	struct clone_args args = {
 		.parent_tid = ptr_to_u64(&parent_tid),
-- 
2.34.1