[LTP] [PATCH v5] coredump01: New core_pattern specifiers test

[LTP] [PATCH v5] 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 v5:
- resolve path from root for helper
- Link to v4: https://lore.kernel.org/20260902-coredump-v4-1-3f511ea1c96a@suse.com

Changes in v4:
- read back core_pattern after writing and abort with TBROK on mismatch
- read CONFIG_STATIC_USERMODEHELPER once in setup() and cache the result
- remove namespace visibility scaffolding and skip logic from verify_pipe_pattern()
- resolve helper path with tst_get_path() instead of /proc/self/exe readlink
- Link to v3: https://lore.kernel.org/20260824-coredump-v3-1-6429da674718@suse.com

Changes in v3:
- check for CONFIG_COREDUMP=y
- Link to v2: https://lore.kernel.org/20260824-coredump-v2-1-42428acf5216@suse.com

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        | 186 ++++++++++++++++++++++++++
 testcases/kernel/coredump/coredump01_helper.c |  66 +++++++++
 6 files changed, 263 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..fcdffd625
--- /dev/null
+++ b/testcases/kernel/coredump/coredump01.c
@@ -0,0 +1,186 @@
+// 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 "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_path[PATH_MAX];
+static char cwd[PATH_MAX];
+static int static_usermodehelper;
+
+static void set_pattern(const char *fmt, ...)
+{
+	char pattern[PATTERN_MAX];
+	char readback[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);
+
+	SAFE_FILE_LINES_SCANF(PATH_KERN_CORE_PATTERN, "%127[^\n]", readback);
+
+	if (strcmp(pattern, readback))
+		tst_brk(TBROK, "core_pattern readback mismatch: wrote '%s', read '%s'",
+			pattern, readback);
+
+	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);
+}
+
+static void verify_pipe_pattern(void)
+{
+	char res[PATH_MAX + 32], exe[PATH_MAX];
+	int pid_seen, sig_seen, elf;
+	long long bytes;
+	pid_t pid;
+
+	if (static_usermodehelper) {
+		tst_res(TCONF, "CONFIG_STATIC_USERMODEHELPER is enabled, skipping pipe core_pattern");
+		return;
+	}
+
+	tst_res(TINFO, "Testing pipe core_pattern");
+
+	set_pattern("|%s %%e %%p %%s %s/res.%%p", helper_path, 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};
+	struct tst_kconfig_var kconfig = TST_KCONFIG_INIT("CONFIG_STATIC_USERMODEHELPER");
+
+	tst_kconfig_read(&kconfig, 1);
+	static_usermodehelper = (kconfig.choice == 'y');
+
+	SAFE_SETRLIMIT(RLIMIT_CORE, &rl);
+
+	SAFE_PRCTL(PR_SET_DUMPABLE, 1, 0, 0, 0);
+
+	SAFE_GETCWD(cwd, sizeof(cwd));
+
+	char path[PATH_MAX];
+
+	if (tst_get_path(HELPER, path, sizeof(path)))
+		tst_brk(TCONF, "'%s' not found in $PATH", HELPER);
+
+	if (!realpath(path, helper_path))
+		tst_brk(TBROK | TERRNO, "realpath(%s) failed", path);
+}
+
+static struct tst_test test = {
+	.test = run,
+	.tcnt = 2,
+	.setup = setup,
+	.needs_root = 1,
+	.needs_tmpdir = 1,
+	.forks_child = 1,
+	.needs_kconfigs = (const char* []) {
+		"CONFIG_COREDUMP=y",
+		NULL,
+	},
+	.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: 12724413534a6d4160ff9694ba6f09daa4ccb6bd
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 Thu, 3 Sep 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

Re: [LTP] [PATCH v5] coredump01: New core_pattern specifiers test

[Li Wang]

Hi Andrea,

> +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);

Generally this checks is really nice, but it'd be better to
add more checks for the core dump file?

e.g. file size > 0, ELF magic valid, and type == ET_CORE.

FYI:

+static int verify_core_dump(const char *path, long long expected_size)
+{
+       int fd;
+       struct stat st;
+       unsigned char magic[SELFMAG];
+       Elf64_Ehdr ehdr;
+
+       if (access(path, F_OK) != 0) {
+               tst_res(TFAIL, "Core dump file %s does not exist", path);
+               return -1;
+       }
+       tst_res(TPASS, "Core dump file %s exists", path);
+
+       SAFE_STAT(path, &st);
+       TST_EXP_EXPR(st.st_size > 0, "core file size = %ld bytes", st.st_size);
+
+       if (expected_size > 0 && st.st_size != expected_size) {
+               tst_res(TFAIL, "Core dump size mismatch: expected %lld bytes, got %ld",
+                       expected_size, st.st_size);
+               return -1;
+       }
+
+       fd = SAFE_OPEN(path, O_RDONLY, 0);
+       SAFE_READ(0, fd, magic, SELFMAG);
+       SAFE_CLOSE(fd);
+
+       TST_EXP_EXPR(!memcmp(magic, ELFMAG, 4),
+                       "core file has valid ELF magic");
+
+       fd = SAFE_OPEN(path, O_RDONLY, 0);
+       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));
+       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));
+       SAFE_CLOSE(fd);
+
+       TST_EXP_EXPR(ehdr.e_type == ET_CORE,
+                       "ELF type is ET_CORE (got %d)", ehdr.e_type);
+
+       return 0;
+}
+
 static void verify_file_pattern(void)
 {
        char dump[PATH_MAX + 32];
@@ -100,11 +140,14 @@ static void verify_file_pattern(void)

        TST_EXP_PASS(access(dump, F_OK), "core.%%e.%%p.%%s expanded to core.coredump01.%d.%d",
                     pid, SIGABRT);
+
+       verify_core_dump(dump, -1);
 }

 static void verify_pipe_pattern(void)
 {
        char res[PATH_MAX + 32], exe[PATH_MAX];
+       char dump[PATH_MAX + 32];
        int pid_seen, sig_seen, elf;
        long long bytes;
        pid_t pid;
@@ -121,6 +164,7 @@ static void verify_pipe_pattern(void)
        pid = crash_child();

        snprintf(res, sizeof(res), "%s/res.%d", cwd, pid);
+       snprintf(dump, sizeof(dump), "%s/res.%d.core", cwd, pid);

        /* the kernel spawns the helper asynchronously */
        if (TST_RETRY_FN_EXP_BACKOFF(access(res, F_OK), TST_RETVAL_EQ0, HELPER_TIMEOUT)) {
@@ -135,6 +179,8 @@ static void verify_pipe_pattern(void)
        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);
+
+       verify_core_dump(dump, bytes);
 }

> +static void verify_pipe_pattern(void)
> +{
> +	char res[PATH_MAX + 32], exe[PATH_MAX];
> +	int pid_seen, sig_seen, elf;
> +	long long bytes;
> +	pid_t pid;
> +
> +	if (static_usermodehelper) {
> +		tst_res(TCONF, "CONFIG_STATIC_USERMODEHELPER is enabled, skipping pipe core_pattern");
> +		return;
> +	}
> +
> +	tst_res(TINFO, "Testing pipe core_pattern");
> +
> +	set_pattern("|%s %%e %%p %%s %s/res.%%p", helper_path, 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);

Here as well.

Also we need do something in the helper to save dump file.

> +}

-- 
Regards,
Li Wang

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

Re: [LTP] [PATCH v5] coredump01: New core_pattern specifiers test

[Andrea Cervesato via ltp]

Hi Li,

> > +	TST_EXP_PASS(access(dump, F_OK), "core.%%e.%%p.%%s expanded to core.coredump01.%d.%d",
> > +		     pid, SIGABRT);
> 
> Generally this checks is really nice, but it'd be better to
> add more checks for the core dump file?
> 
> e.g. file size > 0, ELF magic valid, and type == ET_CORE.

this is already done, but we can introduce ELF type check (read below).

> 
> FYI:
> 
> +static int verify_core_dump(const char *path, long long expected_size)
> +{
> +       int fd;
> +       struct stat st;
> +       unsigned char magic[SELFMAG];
> +       Elf64_Ehdr ehdr;

Ehdr is not portable on 32 bit systems breaking our testing, so I
wouldn't use it in this case. We need Elf32_Half which is in both
32bit and 64bit.

> +
> +       if (access(path, F_OK) != 0) {
> +               tst_res(TFAIL, "Core dump file %s does not exist", path);
> +               return -1;
> +       }
> +       tst_res(TPASS, "Core dump file %s exists", path);
> +
> +       SAFE_STAT(path, &st);
> +       TST_EXP_EXPR(st.st_size > 0, "core file size = %ld bytes", st.st_size);
> +
> +       if (expected_size > 0 && st.st_size != expected_size) {
> +               tst_res(TFAIL, "Core dump size mismatch: expected %lld bytes, got %ld",
> +                       expected_size, st.st_size);
> +               return -1;
> +       }
> +
> +       fd = SAFE_OPEN(path, O_RDONLY, 0);
> +       SAFE_READ(0, fd, magic, SELFMAG);
> +       SAFE_CLOSE(fd);
> +
> +       TST_EXP_EXPR(!memcmp(magic, ELFMAG, 4),
> +                       "core file has valid ELF magic");
> +
> +       fd = SAFE_OPEN(path, O_RDONLY, 0);
> +       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));
> +       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));

double read? I guess it's an error

I will send a new version with some of the proposed checks

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

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Re: [LTP] [PATCH v5] coredump01: New core_pattern specifiers test

[Li Wang]

> > Generally this checks is really nice, but it'd be better to
> > add more checks for the core dump file?
> > 
> > e.g. file size > 0, ELF magic valid, and type == ET_CORE.
> 
> this is already done, but we can introduce ELF type check (read below).

+1

> > +static int verify_core_dump(const char *path, long long expected_size)
> > +{
> > +       int fd;
> > +       struct stat st;
> > +       unsigned char magic[SELFMAG];
> > +       Elf64_Ehdr ehdr;
> 
> Ehdr is not portable on 32 bit systems breaking our testing, so I
> wouldn't use it in this case. We need Elf32_Half which is in both
> 32bit and 64bit.

+1

> > +
> > +       fd = SAFE_OPEN(path, O_RDONLY, 0);
> > +       SAFE_READ(0, fd, magic, SELFMAG);
> > +       SAFE_CLOSE(fd);
> > +
> > +       TST_EXP_EXPR(!memcmp(magic, ELFMAG, 4),
> > +                       "core file has valid ELF magic");
> > +
> > +       fd = SAFE_OPEN(path, O_RDONLY, 0);
> > +       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));
> > +       SAFE_READ(0, fd, &ehdr, sizeof(ehdr));
> 
> double read? I guess it's an error

Oh sorry, that's a duplicate from the vim y&p.

> I will send a new version with some of the proposed checks

Thanks!


-- 
Regards,
Li Wang

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