This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] Avoid concurrency problem in ldconfig (bug 23973)
- From: Christian Brauner <christian at brauner dot io>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Andreas Schwab <schwab at suse dot de>, libc-alpha at sourceware dot org
- Date: Thu, 18 Apr 2019 14:09:59 +0200
- Subject: Re: [PATCH] Avoid concurrency problem in ldconfig (bug 23973)
- References: <mvm5ztmpb3p.fsf@suse.de> <87bm13y11o.fsf@oldenburg2.str.redhat.com>
On Thu, Apr 18, 2019 at 02:01:55PM +0200, Florian Weimer 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.
Just saw this fly by so sorry if I miss the the necessary context: If
there doesn't need to be a file on disk what about using memfd_create()
on kernels that support it?
>
> > 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
> O_EXCL.
>
> > + int fd = mkostemp (temp_name, O_NOFOLLOW);
>
> Likewise.
>
> Thanks,
> Florian