Subject: Re: bug#10257: 23.3.1 Cygwin: network drives - file is write protected (false positive)

From: Ken Brown <[email-masked]>
Date: Wed, 14 Dec 2011 21:53:15 -0500

On 12/14/2011 9:43 PM, Ken Brown wrote:
> On 12/14/2011 12:57 PM, Ken Brown wrote:
>> On 12/14/2011 12:30 PM, Eli Zaretskii wrote:
>>> "Such cases" are those where UID and GID are returned as -1 (I think),
>>> see the original report where Jari shows the result of
>>> file-attributes.
>>
>> OK, I could certainly change check_writable to return success if
>> euidaccess returns failure and UID and GID are both -1. I'll make a
>> patch when I get a chance and let Jari test it.
>
> How does the following patch look?
>
> === modified file 'src/fileio.c'
> --- src/fileio.c 2011-12-05 08:55:25 +0000
> +++ src/fileio.c 2011-12-15 02:17:01 +0000
> @@ -2416,15 +2416,27 @@
> return (st.st_mode & S_IWRITE || S_ISDIR (st.st_mode));
> #else /* not MSDOS */
> #ifdef HAVE_EUIDACCESS
> - return (euidaccess (filename, 2) >= 0);
> -#else
> + int res = (euidaccess (filename, 2) >= 0);
> +#ifdef CYGWIN
> + /* euidaccess may have returned failure because Cygwin couldn't
> + determine the file's UID and GID; if so, we return success. */
> + if (!res)
> + {
> + struct stat st;
> + if (stat (filename, &st) < 0)
> + return 0;
> + res = (st.st_uid == -1 && st.st_gid == -1);
> + }
> +#endif /* CYGWIN */
> + return res;
> +#else /* not HAVE_EUIDACCESS */
> /* Access isn't quite right because it uses the real uid
> and we really want to test with the effective uid.
> But Unix doesn't give us a right way to do it.
> Opening with O_WRONLY could work for an ordinary file,
> but would lose for directories. */
> return (access (filename, 2) >= 0);
> -#endif
> +#endif /* not HAVE_EUIDACCESS */
> #endif /* not MSDOS */
> }

Sorry, this isn't quite right.  I think it's too lenient.  As long as 
I've called stat, I should at least check that stat shows the file to be 
writable, as in the MSDOS port.

I'll send a revised patch.

Ken