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Re: [PATCH] Avoid concurrency problem in ldconfig (bug 23973)
- From: Andreas Schwab <schwab at suse dot de>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Thu, 18 Apr 2019 14:59:46 +0200
- Subject: Re: [PATCH] Avoid concurrency problem in ldconfig (bug 23973)
- References: <email@example.com> <firstname.lastname@example.org>
On Apr 18 2019, Florian Weimer <email@example.com> wrote:
> * Andreas Schwab:
>> Use a unique name for the temporary file when updating the ld.so cache, so
>> that two concurrent runs of ldconfig don't write to the same file.
>> * elf/cache.c (save_cache): Use unique temporary name.
>> (save_aux_cache): Likewise.
> The downside of this change is that if ldconfig is interrupted, the
> temporary file never goes away.
> Ideally, we would use O_TMPFILE if supported by the (file) system, but
> that can get quite involved.
That shortens the window, but won't close it, since we need a name to
pass to rename in any case.
>> diff --git a/elf/cache.c b/elf/cache.c
>> index b8e9e6ccc3..ec7d94b0bc 100644
>> --- a/elf/cache.c
>> +++ b/elf/cache.c
>> @@ -427,12 +427,12 @@ save_cache (const char *cache_name)
>> /* Write out the cache. */
>> /* Write cache first to a temporary file and rename it later. */
>> - char *temp_name = xmalloc (strlen (cache_name) + 2);
>> - sprintf (temp_name, "%s~", cache_name);
>> + char *temp_name;
>> + if (asprintf (&temp_name, "%s.XXXXXX", cache_name) < 0)
>> + error (EXIT_FAILURE, errno, _("Can't allocate temporary name for cache file"));
>> /* Create file. */
>> - int fd = open (temp_name, O_CREAT|O_WRONLY|O_TRUNC|O_NOFOLLOW,
>> - S_IRUSR|S_IWUSR);
>> + int fd = mkostemp (temp_name, O_NOFOLLOW);
> I think you can use mkstemp because O_NOFOLLOW is implied by its use of
Yes, O_NOFOLLOW is useless anyway, since mk[o]stemp is about creating a
Andreas Schwab, SUSE Labs, firstname.lastname@example.org
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