[LTP] [PATCH v5] Refactor fork14 using new LTP API

[Martin Doucha]

Hi,
there's a stale pointer issue in memvec if you run the test with 
multiple iterations. See below.

On 22. 03. 24 10:04, Andrea Cervesato wrote:
> From: Andrea Cervesato <andrea.cervesato@suse.com>
> 
> Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
> ---
> .skip_in_compat usage
> Fixed typos
> Fixed license
> 
>   testcases/kernel/syscalls/fork/fork14.c | 205 +++++++++++-------------
>   1 file changed, 92 insertions(+), 113 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/fork/fork14.c b/testcases/kernel/syscalls/fork/fork14.c
> index 93af2ebac..421f2caa3 100644
> --- a/testcases/kernel/syscalls/fork/fork14.c
> +++ b/testcases/kernel/syscalls/fork/fork14.c
> @@ -1,143 +1,122 @@
> -/*********************************************************************
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
>    * Copyright (C) 2014  Red Hat, Inc.
> - *
> - * This program is free software; you can redistribute it and/or
> - * modify it under the terms of version 2 of the GNU General Public
> - * License as published by the Free Software Foundation.
> - *
> - * This program is distributed in the hope that it would be useful,
> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> - *
> - * Further, this software is distributed without any warranty that it
> - * is free of the rightful claim of any third person regarding
> - * infringement or the like.  Any license provided herein, whether
> - * implied or otherwise, applies only to this software file.  Patent
> - * licenses, if any, provided herein do not apply to combinations of
> - * this program with other software, or any other product whatsoever.
> - *
> - * You should have received a copy of the GNU General Public License
> - * along with this program; if not, write the Free Software
> - * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> - * 02110-1301, USA.
> + * Copyright (C) 2023 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
> + */
> +
> +/*\
> + * [Description]
>    *
>    * This test is a reporducer for this patch:
> - *              https://lkml.org/lkml/2012/4/24/328
> + * https://lore.kernel.org/lkml/1335289853-2923-1-git-send-email-siddhesh.poyarekar@gmail.com/
>    * Since vma length in dup_mmap is calculated and stored in a unsigned
>    * int, it will overflow when length of mmaped memory > 16 TB. When
> - * overflow occur, fork will  incorrectly succeed. The patch above
> - * fixed it.
> - ********************************************************************/
> + * overflow occurs, fork will incorrectly succeed. The patch above fixed it.
> + */
>   
> -#include <sys/mman.h>
> +#include "tst_test.h"
> +#include <stdlib.h>
>   #include <sys/wait.h>
> -#include <stdio.h>
> -#include <unistd.h>
> -#include "test.h"
> -#include "safe_macros.h"
> -#include "lapi/abisize.h"
> -
> -char *TCID = "fork14";
> -int TST_TOTAL = 1;
>   
> -#define GB		(1024 * 1024 * 1024L)
> -
> -/* set mmap threshold to 16TB */
>   #define LARGE		(16 * 1024)
>   #define EXTENT		(16 * 1024 + 10)
>   
> -static char **pointer_vec;
> -
> -static void setup(void);
> -static void cleanup(void);
> -static int  fork_test(void);
> +static char **memvec;
>   
> -int main(int ac, char **av)
> +static void run(void)
>   {
> -	int lc, reproduced;
> +	int i, j, ret;
> +	pid_t pid;
> +	void *mem;
> +	int prev_failed = 0;
> +	int passed = 1;
> +	int failures = 0;
>   
> -	tst_parse_opts(ac, av, NULL, NULL);
> -/*
> - * Tested on ppc64/x86_64/i386/s390x. And only 64bit has this issue.
> - * Since a 32bit program can't mmap so many memory.
> - */
> -#ifdef TST_ABI32
> -	tst_brkm(TCONF, NULL, "This test is only for 64bit.");
> -#endif
> -	setup();
> -	for (lc = 0; TEST_LOOPING(lc); lc++) {
> -		tst_count = 0;
> -
> -		reproduced = fork_test();
> -		if (reproduced == 0)
> -			tst_resm(TPASS, "fork failed as expected.");
> -	}
> -	cleanup();
> -	tst_exit();
> -}
> +	for (i = 0; i < EXTENT; i++) {
> +		mem = mmap(NULL, 1 * TST_GB,
> +			PROT_READ | PROT_WRITE,
> +			MAP_PRIVATE | MAP_ANONYMOUS,
> +			0, 0);
>   
> -static void setup(void)
> -{
> -	tst_sig(FORK, DEF_HANDLER, cleanup);
> -	TEST_PAUSE;
> +		if (mem == MAP_FAILED) {
> +			failures++;
>   
> -	pointer_vec = SAFE_MALLOC(cleanup, EXTENT * sizeof(char *));
> -}
> +			tst_res(TINFO, "mmap() failed");
>   
> -static void cleanup(void)
> -{
> -	free(pointer_vec);
> -}
> +			if (failures > 10) {
> +				tst_brk(TCONF, "mmap() fails too many "
> +					"times, so it's almost impossible to "
> +					"get a vm_area_struct sized 16TB.");
> +			}
>   
> -static int fork_test(void)
> -{
> -	int i, j, prev_failed = 0, fails = 0, cnt = 0;
> -	int reproduced = 0;
> -	void *addr;
> +			continue;
> +		}
>   
> -	for (i = 0; i < EXTENT; i++) {
> -		addr = mmap(NULL, 1 * GB, PROT_READ | PROT_WRITE,
> -			    MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> -		if (addr == MAP_FAILED) {
> -			pointer_vec[i] = NULL;
> -			fails++;
> -			/*
> -			 * EXTENT is "16*1024+10", if fails count exceeds 10,
> -			 * we are almost impossible to get an vm_area_struct
> -			 * sized 16TB
> +		memvec[i] = mem;
> +
> +		pid = fork();
> +
> +		if (pid == -1) {
> +			/* keep track of the failed fork() and verify that next one
> +			 * is failing as well.
>   			 */
> -			if (fails == 11) {
> -				tst_brkm(TCONF, cleanup, "mmap() fails too many"
> -					 "times, so we are almost impossible to"
> -					 " get an vm_area_struct sized 16TB.");
> -			}
> -		} else {
> -			pointer_vec[i] = addr;
> +			prev_failed = 1;
> +			continue;
>   		}
> -		cnt++;
>   
> -		switch (tst_fork()) {
> -		case -1:
> -			prev_failed = 1;
> -		break;
> -		case 0:
> +		if (!pid)
>   			exit(0);
> -		default:
> -			SAFE_WAITPID(cleanup, -1, NULL, 0);
>   
> -			if (prev_failed > 0 && i >= LARGE) {
> -				tst_resm(TFAIL, "Fork succeeds incorrectly");
> -				reproduced = 1;
> -				goto clear_memory_map;
> -			}
> +		ret = waitpid(pid, NULL, 0);
> +		if (ret == -1 && errno != ECHILD)
> +			tst_brk(TBROK | TERRNO, "waitpid() error");
> +
> +		if (prev_failed && i >= LARGE) {
> +			passed = 0;
> +			break;
>   		}
> +
> +		prev_failed = 0;
> +
> +		tst_res(TINFO, "fork() passed at %d attempt", i);
>   	}
>   
> -clear_memory_map:
> -	for (j = 0; j < cnt; j++) {
> -		if (pointer_vec[j])
> -			SAFE_MUNMAP(cleanup, pointer_vec[j], 1 * GB);
> +	for (j = 0; j < i; j++) {
> +		if (memvec[j])
> +			SAFE_MUNMAP(memvec[j], 1 * TST_GB);

The memvec array never gets cleared after setup() so if you run the test 
with multiple iterations (e.g. -i 5), non-NULL pointers will accumulate 
in memvec between test iterations and you may end up unmapping an 
address range that was reused by libc.

>   	}
>   
> -	return reproduced;
> +	if (passed)
> +		tst_res(TPASS, "fork() failed as expected");
> +	else
> +		tst_res(TFAIL, "fork() succeeded incorrectly");
>   }
> +
> +static void setup(void)
> +{
> +	memvec = SAFE_MALLOC(EXTENT * sizeof(char *));
> +	memset(memvec, 0, EXTENT);
> +}
> +
> +static void cleanup(void)
> +{
> +	for (long i = 0; i < EXTENT; i++) {
> +		if (memvec && memvec[i])
> +			SAFE_MUNMAP(memvec[i], 1 * TST_GB);
> +	}
> +
> +	if (memvec)
> +		free(memvec);
> +}
> +
> +static struct tst_test test = {
> +	.test_all = run,
> +	.setup = setup,
> +	.cleanup = cleanup,
> +	.forks_child = 1,
> +	.skip_in_compat = 1,
> +	.tags = (const struct tst_tag[]) {
> +		{"linux-git", "7edc8b0ac16c"},
> +		{}
> +	}
> +};

-- 
Martin Doucha   mdoucha@suse.cz
SW Quality Engineer
SUSE LINUX, s.r.o.
CORSO IIa
Krizikova 148/34
186 00 Prague 8
Czech Republic