On 20/01/2021 01:33, DJ Delorie wrote:
>
> Adhemerval Zanella via Libc-alpha <libc-al...@sourceware.org> writes:
>> - tst-setcontext9 tst-bz20544
>> + tst-setcontext9 tst-bz20544 tst-canon-bz26341
>
> New test, ok.
>
>> +LDLIBS-tst-canon-bz26341 = $(shared-thread-library)
>
> Ok.
>
>> diff --git a/stdlib/tst-canon-bz26341.c b/stdlib/tst-canon-bz26341.c
>
>> +/* Check if realpath does not consume extra stack space based on symlink
>> + existance in the path (BZ #26341)
>
> Is this allowed to be two lines?
Good question. GNU code guidelines does not really restrict a number of
line, it is just says
Also, please write a brief comment at the start of each source file,
with the file name and a line or two about the overall purpose of the file.
We do have other file with two line comments, so I think it should be
fine.
>
>> + Copyright (C) 2020 Free Software Foundation, Inc.
>
> Year is wrong now :-)
Ack.
>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <sys/param.h>
>> +#include <unistd.h>
>
> Ok
>
>> +#define __sysconf sysconf
>> +#include <eloop-threshold.h>
>> +#include <support/check.h>
>> +#include <support/support.h>
>> +#include <support/temp_file.h>
>> +#include <support/xunistd.h>
>> +#include <support/xthread.h>
>
> Ok
>
>> +static char *filename;
>> +static size_t filenamelen;
>> +static char *linkname;
>> +
>> +#ifndef PATH_MAX
>> +# define PATH_MAX 1024
>> +#endif
>
> Ok.
>
>> +static void
>> +create_link (void)
>> +{
>> + int fd = create_temp_file ("tst-canon-bz26341", &filename);
>> + TEST_VERIFY_EXIT (fd != -1);
>> + xclose (fd);
>> +
>> + char *prevlink = filename;
>> + int maxlinks = __eloop_threshold ();
>> + for (int i = 0; i < maxlinks; i++)
>> + {
>> + linkname = xasprintf ("%s%d", filename, i);
>> + xsymlink (prevlink, linkname);
>
> linkname -> prevlink -> filename
>
>> + add_temp_file (linkname);
>> + prevlink = linkname;
>> + }
>> +
>> + filenamelen = strlen (filename);
>> +}
>
> On exit, linkname has the last link created. Needs a comment to that
> effect.
I added prior the link creations.
/* Create MAXLINKS symbolic links to the temporary filename.
On exit, linkname has the last link created. */
>
>
>> +static void *
>> +do_realpath (void *arg)
>> +{
>> + /* Old implementation of realpath allocates a PATH_MAX using alloca
>> + for each symlink in the path, leading to MAXSYMLINKS times PATH_MAX
>> + maximum stack usage.
>> + This stack allocations tries fill the thread allocated stack minus
>> + both the resolved path (plus some slack) and the realpath (plus some
>> + slack).
>> + If realpath uses more than 2 * PATH_MAX plus some slack it will trigger
>> + a stackoverflow. */
>> +
>> + const size_t realpath_usage = 2 * PATH_MAX + 1024;
>> + const size_t thread_usage = 1 * PATH_MAX + 1024;
>> + size_t stack_size = support_small_thread_stack_size ()
>> + - realpath_usage - thread_usage;
>> + char stack[stack_size];
>> + char *resolved = stack + stack_size - thread_usage + 1024;
>
> This points us at PATH_MAX away from the end of stack[]. Ok. Also
> forces most of the stack to get used up :-)
>
>> + char *p = realpath (linkname, resolved);
>
> We assume the test will crash if we use more stack than we allocated.
>
>> + TEST_VERIFY (p != NULL);
>
> realpath() must succeed, ok
>
>> + TEST_COMPARE_BLOB (resolved, filenamelen, filename, filenamelen);
>
> And give us the right result, ok
>
>> + return NULL;
>> +}
>> +
>> +static int
>> +do_test (void)
>> +{
>> + create_link ();
>> +
>> + pthread_t th = xpthread_create (support_small_stack_thread_attribute (),
>> + do_realpath, NULL);
>> + xpthread_join (th);
>> +
>> + return 0;
>> +}
>
> Run the test in a thread with a small stack, ok.
>
>> +#include <support/test-driver.c>
>
> LGTM with that comment.
>
> Reviewed-by: DJ Delorie <d...@redhat.com>
>
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