Re: [LTP] coredump01: New core_pattern specifiers test

Re: [LTP] coredump01: New core_pattern specifiers test

[linuxtestproject.agent]

Hi Andrea,

On Aug 20, 2026, Andrea Cervesato wrote:
> coredump01: New core_pattern specifiers test

> 	ssize_t rval, i;
> 	int fd, elf;
>
> 	if (bytes >= 4 && !memcmp(magic, "\177ELF", 4))
> 		elf = 1;
>
> 	dprintf(fd, "exe=%s pid=%s sig=%s bytes=%lld elf=%d\n",
> 		argv[1], argv[2], argv[3], bytes, elf);

Could `elf` be initialized to zero? For short or non-ELF input the
condition does not assign it, so `dprintf()` reads an indeterminate value.
A nonzero value can make the test accept a malformed core stream as ELF.

> 	SAFE_PRCTL(PR_GET_DUMPABLE, 1, 0, 0, 0);

Should this use `PR_SET_DUMPABLE`? `PR_GET_DUMPABLE` only returns the
current state and ignores arg2, so this call does not ensure that
`abort()` can produce a core dump.

> 	/* the kernel spawns the helper asynchronously */
> 	if (TST_RETRY_FN_EXP_BACKOFF(access(res, F_OK), TST_RETVAL_EQ0, HELPER_TIMEOUT)) {
> 		tst_res(TFAIL, "%s did not report any core dump", HELPER);

Could kernels with `CONFIG_STATIC_USERMODEHELPER` be rejected with TCONF
before this check? In particular, an empty
`CONFIG_STATIC_USERMODEHELPER_PATH` intentionally disables the helper, so
this timeout reports TFAIL without testing specifier expansion.

> 	set_pattern("|%s/%s %%e %%p %%s %s/res.%%p", helper_dir, HELPER, cwd);
>
> 	len = SAFE_READLINK("/proc/self/exe", helper_dir, sizeof(helper_dir) - 1);

Could the pipe case require the initial mount namespace, or otherwise use
paths visible there? The kernel resolves and runs a `core_pattern` pipe
handler in the initial mount namespace. If LTP runs in another mount
namespace, these helper and result paths may not exist there, producing a
spurious TFAIL.

> /*
>  * Core dump collector for the piped core_pattern tested by coredump01.
>  *
>  * Avoiding the LTP API here is correct, since the kernel spawns the helper
>  * through ``call_usermodehelper()`` without the LTP IPC environment.
>  */
>
> int main(int argc, char *argv[])

Could this helper follow the LTP helper-binary convention by defining
`TST_NO_DEFAULT_MAIN` and including `tst_test.h`? The missing IPC
environment means it should avoid IPC-backed result calls, but does not
require avoiding the helper API form itself.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] coredump01: New core_pattern specifiers test

[Andrea Cervesato via ltp]

> > 	ssize_t rval, i;
> > 	int fd, elf;
> >
> > 	if (bytes >= 4 && !memcmp(magic, "\177ELF", 4))
> > 		elf = 1;
> >
> > 	dprintf(fd, "exe=%s pid=%s sig=%s bytes=%lld elf=%d\n",
> > 		argv[1], argv[2], argv[3], bytes, elf);
> 
> Could `elf` be initialized to zero? For short or non-ELF input the
> condition does not assign it, so `dprintf()` reads an indeterminate value.
> A nonzero value can make the test accept a malformed core stream as ELF.

This can be fixed.

> 
> > 	SAFE_PRCTL(PR_GET_DUMPABLE, 1, 0, 0, 0);
> 
> Should this use `PR_SET_DUMPABLE`? `PR_GET_DUMPABLE` only returns the
> current state and ignores arg2, so this call does not ensure that
> `abort()` can produce a core dump.
> 
> > 	/* the kernel spawns the helper asynchronously */
> > 	if (TST_RETRY_FN_EXP_BACKOFF(access(res, F_OK), TST_RETVAL_EQ0, HELPER_TIMEOUT)) {
> > 		tst_res(TFAIL, "%s did not report any core dump", HELPER);
> 
> Could kernels with `CONFIG_STATIC_USERMODEHELPER` be rejected with TCONF
> before this check? In particular, an empty
> `CONFIG_STATIC_USERMODEHELPER_PATH` intentionally disables the helper, so
> this timeout reports TFAIL without testing specifier expansion.

This can be added in needs_kconfig.

> 
> > 	set_pattern("|%s/%s %%e %%p %%s %s/res.%%p", helper_dir, HELPER, cwd);
> >
> > 	len = SAFE_READLINK("/proc/self/exe", helper_dir, sizeof(helper_dir) - 1);
> 
> Could the pipe case require the initial mount namespace, or otherwise use
> paths visible there? The kernel resolves and runs a `core_pattern` pipe
> handler in the initial mount namespace. If LTP runs in another mount
> namespace, these helper and result paths may not exist there, producing a
> spurious TFAIL.
> 
> > /*
> >  * Core dump collector for the piped core_pattern tested by coredump01.
> >  *
> >  * Avoiding the LTP API here is correct, since the kernel spawns the helper
> >  * through ``call_usermodehelper()`` without the LTP IPC environment.
> >  */
> >
> > int main(int argc, char *argv[])
> 
> Could this helper follow the LTP helper-binary convention by defining
> `TST_NO_DEFAULT_MAIN` and including `tst_test.h`? The missing IPC
> environment means it should avoid IPC-backed result calls, but does not
> require avoiding the helper API form itself.

It doesn't make any sense. We can skip this one.

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

[LTP] [PATCH v2] coredump01: New core_pattern specifiers test

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

LTP has no coverage for the core_pattern specifiers expansion, neither
for the pipe flavor of core_pattern, where the kernel spawns a user
space helper and writes the core dump into its standard input.

The new test verifies that %e, %p and %s are expanded both in the core
file name and in the arguments of a piped helper, checking also that
the helper really receives an ELF core dump.

Root is required to rewrite the system wide core_pattern, which is
restored by the test library on all exit paths.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
Add a simple coredump01 test that simulate a coredump and verify that it
actually works. This is a small coverage that is missing inside LTP
testing suite.
---
Changes in v2:
- fix CI agent spotted errors
- Link to v1: https://lore.kernel.org/20260820-coredump-v1-1-7ce51603cefb@suse.com
---
 runtest/kernel_misc                           |   1 +
 testcases/kernel/Makefile                     |   1 +
 testcases/kernel/coredump/.gitignore          |   2 +
 testcases/kernel/coredump/Makefile            |   7 +
 testcases/kernel/coredump/coredump01.c        | 221 ++++++++++++++++++++++++++
 testcases/kernel/coredump/coredump01_helper.c |  66 ++++++++
 6 files changed, 298 insertions(+)

diff --git a/runtest/kernel_misc b/runtest/kernel_misc
index cc3562cb7..ecf9ee2a2 100644
--- a/runtest/kernel_misc
+++ b/runtest/kernel_misc
@@ -17,3 +17,4 @@ zram02 zram02.sh
 zram03 zram03
 umip_basic_test umip_basic_test
 aslr01 aslr01
+coredump01 coredump01
diff --git a/testcases/kernel/Makefile b/testcases/kernel/Makefile
index ac816e4e8..6b303c14b 100644
--- a/testcases/kernel/Makefile
+++ b/testcases/kernel/Makefile
@@ -19,6 +19,7 @@ SUBDIRS			+= lib
 SUBDIRS			+= connectors \
 			   containers \
 			   controllers \
+			   coredump \
 			   crypto \
 			   device-drivers \
 			   firmware \
diff --git a/testcases/kernel/coredump/.gitignore b/testcases/kernel/coredump/.gitignore
new file mode 100644
index 000000000..cd0b51700
--- /dev/null
+++ b/testcases/kernel/coredump/.gitignore
@@ -0,0 +1,2 @@
+/coredump01
+/coredump01_helper
diff --git a/testcases/kernel/coredump/Makefile b/testcases/kernel/coredump/Makefile
new file mode 100644
index 000000000..951a3e976
--- /dev/null
+++ b/testcases/kernel/coredump/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2026 Linux Test Project
+
+top_srcdir		?= ../../..
+
+include $(top_srcdir)/include/mk/testcases.mk
+include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/kernel/coredump/coredump01.c b/testcases/kernel/coredump/coredump01.c
new file mode 100644
index 000000000..a958d8307
--- /dev/null
+++ b/testcases/kernel/coredump/coredump01.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 Linux Test Project
+ */
+
+/*\
+ * Verify that the kernel expands the :manpage:`core(5)` specifiers %e
+ * (executable name), %p (PID) and %s (signal number) when it creates a
+ * core dump.
+ *
+ * Both flavors of ``/proc/sys/kernel/core_pattern`` are tested:
+ *
+ * - a plain file name, where the specifiers become part of the core file
+ *   name
+ * - a pipe to a user space helper, where the specifiers are expanded in
+ *   the helper arguments and the core dump is written to the helper
+ *   standard input
+ *
+ * The test needs root because it rewrites the system wide core_pattern.
+ * The original value is saved and restored by the test library on all
+ * exit paths.
+ *
+ * [Algorithm]
+ *
+ * - Point core_pattern into the test temporary directory
+ * - Fork a child which aborts itself to produce a core dump
+ * - For the file pattern check that ``core.<exe>.<pid>.<signal>`` was created
+ * - For the pipe pattern check the arguments the helper was called with
+ *   and that it received an ELF core dump on its standard input
+ */
+
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "tst_test.h"
+#include "tst_kconfig.h"
+#include "lapi/prctl.h"
+
+#define PATTERN_MAX 128
+#define HELPER "coredump01_helper"
+#define HELPER_TIMEOUT 10
+
+static char helper_dir[PATH_MAX];
+static char cwd[PATH_MAX];
+
+static void set_pattern(const char *fmt, ...)
+{
+	char pattern[PATTERN_MAX];
+	va_list va;
+	int len;
+
+	va_start(va, fmt);
+	len = vsnprintf(pattern, sizeof(pattern), fmt, va);
+	va_end(va);
+
+	if (len >= PATTERN_MAX)
+		tst_brk(TCONF, "core_pattern does not fit into %i bytes", PATTERN_MAX - 1);
+
+	SAFE_FILE_PRINTF(PATH_KERN_CORE_PATTERN, "%s", pattern);
+
+	tst_res(TINFO, "core_pattern is '%s'", pattern);
+}
+
+static pid_t crash_child(void)
+{
+	int status;
+	pid_t pid;
+
+	pid = SAFE_FORK();
+	if (!pid)
+		abort();
+
+	SAFE_WAITPID(pid, &status, 0);
+
+	if (!WIFSIGNALED(status) || !WCOREDUMP(status))
+		tst_brk(TFAIL, "Child did not dump core");
+
+	return pid;
+}
+
+static void verify_file_pattern(void)
+{
+	char dump[PATH_MAX + 32];
+	pid_t pid;
+
+	tst_res(TINFO, "Testing file core_pattern");
+
+	set_pattern("%s/core.%%e.%%p.%%s", cwd);
+
+	pid = crash_child();
+
+	snprintf(dump, sizeof(dump), "%s/core.coredump01.%d.%d", cwd, pid, SIGABRT);
+
+	TST_EXP_PASS(access(dump, F_OK), "core.%%e.%%p.%%s expanded to core.coredump01.%d.%d",
+		     pid, SIGABRT);
+}
+
+/* PID 2 is kthreadd only if we can see the initial PID namespace */
+static int have_init_pid_ns(void)
+{
+	char comm[16] = {0};
+	int fd, len;
+
+	fd = open("/proc/2/comm", O_RDONLY);
+	if (fd < 0)
+		return 0;
+
+	len = SAFE_READ(0, fd, comm, sizeof(comm) - 1);
+	SAFE_CLOSE(fd);
+
+	return len > 0 && !strncmp(comm, "kthreadd\n", 9);
+}
+
+/*
+ * The kernel resolves @path the way /proc/2/root (kthreadd lives in the
+ * initial namespaces) resolves it.
+ */
+static int same_in_init_mnt_ns(const char *path)
+{
+	char init_path[PATH_MAX + 32];
+	struct stat our_st, init_st;
+
+	SAFE_STAT(path, &our_st);
+
+	snprintf(init_path, sizeof(init_path), "/proc/2/root%s", path);
+
+	if (stat(init_path, &init_st))
+		return 0;
+
+	return init_st.st_dev == our_st.st_dev && init_st.st_ino == our_st.st_ino;
+}
+
+static void verify_pipe_pattern(void)
+{
+	char res[PATH_MAX + 32], exe[PATH_MAX], helper[PATH_MAX + 32];
+	struct tst_kconfig_var kconfig = TST_KCONFIG_INIT("CONFIG_STATIC_USERMODEHELPER");
+	int pid_seen, sig_seen, elf;
+	long long bytes;
+	pid_t pid;
+
+	tst_kconfig_read(&kconfig, 1);
+	if (kconfig.choice == 'y') {
+		tst_res(TCONF, "CONFIG_STATIC_USERMODEHELPER is enabled, skipping pipe core_pattern");
+		return;
+	}
+
+	snprintf(helper, sizeof(helper), "%s/%s", helper_dir, HELPER);
+
+	/*
+	 * The kernel always execs the pipe helper in the initial mount
+	 * namespace (core(5)), no matter where the crashing process lives.
+	 * Skip unless both the helper and the result directory are the very
+	 * same objects there, otherwise the kernel would not find them and
+	 * the test would fail spuriously, e.g. inside a container.
+	 */
+	if (!have_init_pid_ns() || !same_in_init_mnt_ns(helper) ||
+	    !same_in_init_mnt_ns(cwd)) {
+		tst_res(TCONF, "Pipe helper or result dir not visible in the initial mount namespace");
+		return;
+	}
+
+	tst_res(TINFO, "Testing pipe core_pattern");
+
+	set_pattern("|%s/%s %%e %%p %%s %s/res.%%p", helper_dir, HELPER, cwd);
+
+	pid = crash_child();
+
+	snprintf(res, sizeof(res), "%s/res.%d", cwd, pid);
+
+	/* the kernel spawns the helper asynchronously */
+	if (TST_RETRY_FN_EXP_BACKOFF(access(res, F_OK), TST_RETVAL_EQ0, HELPER_TIMEOUT)) {
+		tst_res(TFAIL, "%s did not report any core dump", HELPER);
+		return;
+	}
+
+	SAFE_FILE_SCANF(res, "exe=%15s pid=%d sig=%d bytes=%lld elf=%d",
+			exe, &pid_seen, &sig_seen, &bytes, &elf);
+
+	TST_EXP_EQ_STR(exe, "coredump01");
+	TST_EXP_EQ_LI(pid_seen, pid);
+	TST_EXP_EQ_LI(sig_seen, SIGABRT);
+	TST_EXP_EXPR(elf && bytes > 0, "%s read %lli bytes of ELF core dump", HELPER, bytes);
+}
+
+static void run(unsigned int n)
+{
+	if (n)
+		verify_pipe_pattern();
+	else
+		verify_file_pattern();
+}
+
+static void setup(void)
+{
+	struct rlimit rl = {RLIM_INFINITY, RLIM_INFINITY};
+	ssize_t len;
+
+	SAFE_SETRLIMIT(RLIMIT_CORE, &rl);
+
+	SAFE_PRCTL(PR_SET_DUMPABLE, 1, 0, 0, 0);
+
+	SAFE_GETCWD(cwd, sizeof(cwd));
+
+	len = SAFE_READLINK("/proc/self/exe", helper_dir, sizeof(helper_dir) - 1);
+	helper_dir[len] = '\0';
+	*strrchr(helper_dir, '/') = '\0';
+}
+
+static struct tst_test test = {
+	.test = run,
+	.tcnt = 2,
+	.setup = setup,
+	.needs_root = 1,
+	.needs_tmpdir = 1,
+	.forks_child = 1,
+	.save_restore = (const struct tst_path_val[]) {
+		{PATH_KERN_CORE_PATTERN, NULL, TST_SR_TCONF},
+		{}
+	},
+};
diff --git a/testcases/kernel/coredump/coredump01_helper.c b/testcases/kernel/coredump/coredump01_helper.c
new file mode 100644
index 000000000..41091b428
--- /dev/null
+++ b/testcases/kernel/coredump/coredump01_helper.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 Linux Test Project
+ */
+
+/*
+ * Core dump collector for the piped core_pattern tested by coredump01.
+ *
+ * Avoiding the LTP API here is correct, since the kernel spawns the helper
+ * through ``call_usermodehelper()`` without the LTP IPC environment.
+ *
+ * The helper is called as:
+ *
+ *	coredump01_helper <exe> <pid> <signal> <result file>
+ *
+ * and stores what it received in the result file, which is published with
+ * :manpage:`rename()` so that the polling test never reads a partial line.
+ */
+
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[])
+{
+	char buf[4096], tmp[PATH_MAX], magic[4];
+	long long bytes = 0;
+	ssize_t rval, i;
+	int fd, elf = 0;
+
+	if (argc < 5)
+		return 1;
+
+	/*
+	 * A core dump embeds the ELF images it has mapped, so the magic is
+	 * only meaningful at the very beginning of the stream. Collect it
+	 * across reads, since a pipe read can return less than 4 bytes.
+	 */
+	while ((rval = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
+		for (i = 0; i < rval && bytes + i < 4; i++)
+			magic[bytes + i] = buf[i];
+
+		bytes += rval;
+	}
+
+	if (rval < 0)
+		return 1;
+
+	if (bytes >= 4 && !memcmp(magic, "\177ELF", 4))
+		elf = 1;
+
+	snprintf(tmp, sizeof(tmp), "%s.tmp", argv[4]);
+
+	fd = open(tmp, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+	if (fd < 0)
+		return 1;
+
+	dprintf(fd, "exe=%s pid=%s sig=%s bytes=%lld elf=%d\n",
+		argv[1], argv[2], argv[3], bytes, elf);
+
+	close(fd);
+
+	return rename(tmp, argv[4]) ? 1 : 0;
+}

---
base-commit: e62b1a4731f9c458d65c2659d2f8bb58b93e6d6d
change-id: 20260820-coredump-22fc731bde08

Best regards,
--  
Andrea Cervesato <andrea.cervesato@suse.com>


-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] coredump01: New core_pattern specifiers test

[linuxtestproject.agent]

Hi Andrea,

On August 24, 2026, Andrea Cervesato wrote:
> coredump01: New core_pattern specifiers test

> static struct tst_test test = {
> 	.test = run,
> 	.tcnt = 2,
> 	.setup = setup,
> 	.needs_root = 1,
> 	.needs_tmpdir = 1,
> 	.forks_child = 1,
> 	.save_restore = (const struct tst_path_val[]) {

Could this add a CONFIG_COREDUMP=y entry to .needs_kconfigs?
Without it, the ELF binary format has no core-dump callback, so
vfs_coredump() returns without setting the WCOREDUMP status bit.
crash_child() then reports TFAIL rather than TCONF on a valid kernel
configuration.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] coredump01: New core_pattern specifiers test

[linuxtestproject.agent]

Hi Andrea,

On Mon, 24 Aug 2026, Andrea Cervesato wrote:
> coredump01: New core_pattern specifiers test

Verdict - Reviewed

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp