bin/124409: fsck(8) requires exact entry for mountpoints when executing / bug by design in getfsfile(3) in .../lib/libc/gen/fstab.c

[Giorgos Keramidas]

On Mon, 16 Jun 2008 20:28:08 -0700, "Garrett Cooper" <yanefbsd at gmail.com> wrote:
> On Tue, Jun 10, 2008 at 2:27 AM, Garrett Cooper <yanefbsd at gmail.com> wrote:
>> Ok.... it appears I wasn't intelligent enough to post this in the right
>> place last night. Comments please?
>>
>> Hi hackers,
>>
>>      I have a question, pending a bug found in getfsfile(3) [1].
>>
>>      Is there any possibility where a mountpoint be any value other
>>
>> than a directory, a symlink, or "none", i.e. a flat file?
>>
>> Thanks,
>>
>> -Garrett
>>
>> References:
>>
>> http://www.freebsd.org/cgi/query-pr.cgi?pr=bin/124409 (not fully in PR
>>
>> database yet).
>
> Going once, going twice...

Hi Garrett :-)

When I wrote the original comment in that PR I had something like this
in mind:

%%%
*** src.7789d2851415/lib/libc/gen/fstab.c	Sun Jun 22 05:57:09 2008
--- /home/build/src/lib/libc/gen/fstab.c	Sun Jun 22 05:56:48 2008
*************** struct fstab *
*** 236,245 ****
  getfsfile(name)
  	const char *name;
  {
  	if (setfsent())
! 		while (fstabscan())
! 			if (!strcmp(_fs_fstab.fs_file, name))
  				return(&_fs_fstab);
  	return((struct fstab *)NULL);
  }
  
--- 236,256 ----
  getfsfile(name)
  	const char *name;
  {
+ 	char name_path[PATH_MAX];
+ 	char fstab_path[PATH_MAX];
+ 
+ 	if (realpath(name, name_path) == NULL)
+ 		return((struct fstab *)NULL);
  	if (setfsent())
! 		while (fstabscan()) {
! 			if (strcmp(_fs_fstab.fs_file, name) == 0 ||
! 			    strcmp(_fs_fstab.fs_file, name_path) == 0)
! 				return(&_fs_fstab);
! 			if (realpath(_fs_fstab.fs_file, fstab_path) == NULL)
! 				return((struct fstab *)NULL);
! 			if (strcmp(fstab_path, name_path) == 0)
  				return(&_fs_fstab);
+ 		}
  	return((struct fstab *)NULL);
  }
  
%%%

I tried to avoid unnecessary realpath(3) calls as much as possible, but
there is still the possibility for at least N+1 calls, where N is the
number of entries in fstab...

Can you test the above patch, and let me know if it looks ok, if you
have a better fix in the works, etc.?  It seems to pass the bug you
originally reported when I run:

    % env LD_PRELOAD=/home/build/obj/home/build/src/lib/libc/libc.so.7 \
        fsck ///cdrom///
    fsck: exec fsck_cd9660 for /dev/acd0 in /sbin:/usr/sbin: No such file or directory

The failure later is ok, because we don't have fsck_cd9660 for CD-ROMs.