selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 126 insertions, 0 deletions

diff --git a/tools/testing/selftests/filelock/.gitignore b/tools/testing/selftests/filelock/.gitignore
new file mode 100644
index 000000000..825e899a1
--- /dev/null
+++ b/tools/testing/selftests/filelock/.gitignore
@@ -0,0 +1 @@
+ofdlocks
diff --git a/tools/testing/selftests/filelock/Makefile b/tools/testing/selftests/filelock/Makefile
new file mode 100644
index 000000000..478e82f8b
--- /dev/null
+++ b/tools/testing/selftests/filelock/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_GEN_PROGS := ofdlocks
+
+include ../lib.mk
diff --git a/tools/testing/selftests/filelock/ofdlocks.c b/tools/testing/selftests/filelock/ofdlocks.c
new file mode 100644
index 000000000..68bac28b2
--- /dev/null
+++ b/tools/testing/selftests/filelock/ofdlocks.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include "kselftest.h"
+
+static int lock_set(int fd, struct flock *fl)
+{
+	int ret;
+
+	fl->l_pid = 0;		// needed for OFD locks
+	fl->l_whence = SEEK_SET;
+	ret = fcntl(fd, F_OFD_SETLK, fl);
+	if (ret)
+		ksft_perror("fcntl()");
+	return ret;
+}
+
+static int lock_get(int fd, struct flock *fl)
+{
+	int ret;
+
+	fl->l_pid = 0;		// needed for OFD locks
+	fl->l_whence = SEEK_SET;
+	ret = fcntl(fd, F_OFD_GETLK, fl);
+	if (ret)
+		ksft_perror("fcntl()");
+	return ret;
+}
+
+int main(void)
+{
+	int rc;
+	struct flock fl, fl2;
+	int fd = open("/tmp/aa", O_RDWR | O_CREAT | O_EXCL, 0600);
+	int fd2 = open("/tmp/aa", O_RDONLY);
+
+	ksft_print_header();
+	ksft_set_plan(4);
+
+	unlink("/tmp/aa");
+	assert(fd != -1);
+	assert(fd2 != -1);
+	ksft_print_msg("opened fds %i %i\n", fd, fd2);
+
+	/* Set some read lock */
+	fl.l_type = F_RDLCK;
+	fl.l_start = 5;
+	fl.l_len = 3;
+	rc = lock_set(fd, &fl);
+	ksft_test_result(rc == 0, "set OFD read lock on first fd\n");
+	if (rc != 0)
+		ksft_finished();
+
+	/* Make sure read locks do not conflict on different fds. */
+	fl.l_type = F_RDLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd2, &fl);
+	if (rc != 0)
+		ksft_finished();
+	if (fl.l_type != F_UNLCK)
+		ksft_exit_fail_msg("read locks conflicted\n");
+
+	/* Make sure read/write locks do conflict on different fds. */
+	fl.l_type = F_WRLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd2, &fl);
+	if (rc != 0)
+		ksft_finished();
+	ksft_test_result(fl.l_type != F_UNLCK,
+			 "read and write locks conflicted\n");
+	if (fl.l_type == F_UNLCK)
+		ksft_finished();
+
+	/* Get info about the lock on first fd. */
+	fl.l_type = F_UNLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd, &fl);
+	if (rc != 0)
+		ksft_exit_fail_msg("F_OFD_GETLK with F_UNLCK not supported\n");
+	ksft_test_result(fl.l_type != F_UNLCK,
+			 "F_OFD_GETLK with F_UNLCK returned lock info\n");
+	if (fl.l_type == F_UNLCK)
+		ksft_exit_fail();
+	ksft_print_msg("F_UNLCK test returns: locked, type %i pid %i len %zi\n",
+		       fl.l_type, fl.l_pid, fl.l_len);
+
+	/* Try the same but by locking everything by len==0. */
+	fl2.l_type = F_UNLCK;
+	fl2.l_start = 0;
+	fl2.l_len = 0;
+	rc = lock_get(fd, &fl2);
+	if (rc != 0)
+		ksft_exit_fail_msg
+		    ("F_OFD_GETLK with F_UNLCK not supported\n");
+	ksft_test_result(memcmp(&fl, &fl2, sizeof(fl)) == 0,
+			 "F_UNLCK with len==0 returned the same\n");
+	if (memcmp(&fl, &fl2, sizeof(fl))) {
+		ksft_exit_fail_msg
+		    ("F_UNLCK test returns: locked, type %i pid %i len %zi\n",
+		     fl.l_type, fl.l_pid, fl.l_len);
+	}
+
+	/* Get info about the lock on second fd - no locks on it. */
+	fl.l_type = F_UNLCK;
+	fl.l_start = 0;
+	fl.l_len = 0;
+	lock_get(fd2, &fl);
+	ksft_test_result(fl.l_type == F_UNLCK,
+			 "F_OFD_GETLK with F_UNLCK return lock info from another fd\n");
+
+	ksft_finished();
+}