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selftests:core: test coverage for dup_fd() failure handling in unshare_fd()

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At some point there'd been a dumb braino during the dup_fd()
calling conventions change; caught by smatch and immediately fixed.
The trouble is, there had been no test coverage for the dup_fd() failure
handling - neither in kselftests nor in LTP.  Fortunately, it can be
triggered on stock kernel - ENOMEM would require fault injection, but
EMFILE can be had with sysctl alone (fs.nr_open).

Add a test for dup_fd() failure.
Fixed up commit log and short log - Shuah Khan

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
This commit is contained in:
Al Viro 2024-08-22 05:39:32 +01:00 • committed by Shuah Khan
parent c049acee3c
commit 611fbeb44a
2 changed files with 95 additions and 1 deletions
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2
tools/testing/selftests/core/Makefile
View file

@ -1,7 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
CFLAGS += -g $(KHDR_INCLUDES)
TEST_GEN_PROGS := close_range_test
TEST_GEN_PROGS := close_range_test unshare_test
include ../lib.mk

94
tools/testing/selftests/core/unshare_test.c Normal file
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@ -0,0 +1,94 @@
// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/kernel.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syscall.h>
#include <unistd.h>
#include <sys/resource.h>
#include <linux/close_range.h>
#include "../kselftest_harness.h"
#include "../clone3/clone3_selftests.h"
TEST(unshare_EMFILE)
{
pid_t pid;
int status;
struct __clone_args args = {
.flags = CLONE_FILES,
.exit_signal = SIGCHLD,
};
int fd;
ssize_t n, n2;
static char buf[512], buf2[512];
struct rlimit rlimit;
int nr_open;
fd = open("/proc/sys/fs/nr_open", O_RDWR);
ASSERT_GE(fd, 0);
n = read(fd, buf, sizeof(buf));
ASSERT_GT(n, 0);
ASSERT_EQ(buf[n - 1], '\n');
ASSERT_EQ(sscanf(buf, "%d", &nr_open), 1);
ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit));
/* bump fs.nr_open */
n2 = sprintf(buf2, "%d\n", nr_open + 1024);
lseek(fd, 0, SEEK_SET);
write(fd, buf2, n2);
/* bump ulimit -n */
rlimit.rlim_cur = nr_open + 1024;
rlimit.rlim_max = nr_open + 1024;
EXPECT_EQ(0, setrlimit(RLIMIT_NOFILE, &rlimit)) {
lseek(fd, 0, SEEK_SET);
write(fd, buf, n);
exit(EXIT_FAILURE);
}
/* get a descriptor past the old fs.nr_open */
EXPECT_GE(dup2(2, nr_open + 64), 0) {
lseek(fd, 0, SEEK_SET);
write(fd, buf, n);
exit(EXIT_FAILURE);
}
/* get descriptor table shared */
pid = sys_clone3(&args, sizeof(args));
EXPECT_GE(pid, 0) {
lseek(fd, 0, SEEK_SET);
write(fd, buf, n);
exit(EXIT_FAILURE);
}
if (pid == 0) {
int err;
/* restore fs.nr_open */
lseek(fd, 0, SEEK_SET);
write(fd, buf, n);
/* ... and now unshare(CLONE_FILES) must fail with EMFILE */
err = unshare(CLONE_FILES);
EXPECT_EQ(err, -1)
exit(EXIT_FAILURE);
EXPECT_EQ(errno, EMFILE)
exit(EXIT_FAILURE);
exit(EXIT_SUCCESS);
}
EXPECT_EQ(waitpid(pid, &status, 0), pid);
EXPECT_EQ(true, WIFEXITED(status));
EXPECT_EQ(0, WEXITSTATUS(status));
}
TEST_HARNESS_MAIN