From: Frans Klaver <fransklaver@gmail.com>
Date: Wed, 07 Dec 2011 08:31:24 GMT
Subject: Re: [PATCH 1/2] run-command: Add checks after execvp fails with EACCES
Message-ID: <CAH6sp9NsRDWoMtnBUXOP-OMFwjjUm-OuRLpNvcS4pC1S=C93EQ@mail.gmail.com>
In-Reply-To: <7vpqg1e3au.fsf@alter.siamese.dyndns.org>

Thanks for the review. There's a lot of things you mention that I
either didn't see (staring blind, you know) or that I didn't know of.

On Tue, Dec 6, 2011 at 11:35 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Frans Klaver <fransklaver@gmail.com> writes:
>
>> +#ifndef WIN32
>> +static int is_in_group(gid_t gid)
>> ...
>> +static int have_read_execute_permissions(const char *path)
>> +{
>> +     struct stat s;
>> +     trace_printf("checking '%s'\n", path);
>> +
>> +     if (stat(path, &s) < 0) {
>> + ...
>> +     /* check world permissions */
>> +     if ((s.st_mode&(S_IXOTH|S_IROTH)) == (S_IXOTH|S_IROTH))
>> +             return 1;
>
> Hmm, do you need to do this with stat(2)?
>
> Wouldn't access(2) with R_OK|X_OK give you exactly what you want without
> this much trouble?

Probably. I'll use access instead in a reroll.


> I also think that your permission check is incorrectly implemented.
>
>    $ cd /var/tmp && date >j && chmod 044 j && ls -l j
>    ----r--r-- 1 junio junio 29 Dec  6 14:32 j
>    $ cat j
>    cat: j: Permission denied
>    $ su pogo
>    Password:
>    $ cat j
>    Tue Dec  6 14:32:23 PST 2011
>
> That's a world-readable but unreadable-only-to-me file.

Hmm, this is a case that didn't fit my expectations. Thanks for catching.



>> +static void diagnose_execvp_eacces(const char *cmd, const char **argv)
>> +{
>> +     /* man 2 execve states that EACCES is returned for:
>
>        /*
>         * Just a style, but we tend to write multi-line comment like
>         * this, without anything else on opening and closing lines of
>         * the comment block.
>         */
>
>> +      * - The file system is mounted noexec
>> +      */
>> +     struct strbuf sb = STRBUF_INIT;
>> +     char *path = getenv("PATH");
>> +     char *next;
>> +
>> +     if (strchr(cmd, '/')) {
>> +             if (!have_read_execute_permissions(cmd))
>> +                     error("no read/execute permissions on '%s'\n", cmd);
>> +             return;
>> +     }
>
> Ok, execvp() failed and "cmd" has at least one slash, so we know we did
> not look for it in $PATH.  We check only one and return (did you need
> getenv() in that case?).

Obviously not. Missed that.

>
>> +     for (;;) {
>> +             next = strchrnul(path, ':');
>> +             if (path < next)
>> +                     strbuf_add(&sb, path, next - path);
>> +             else
>> +                     strbuf_addch(&sb, '.');
>
> Nice touch that you did not forget an empty component on $PATH.

Yes, that's a relic from me starting work based on one of your
proposed patches[1]. So that one goes to you.

[1] http://article.gmane.org/gmane.comp.version-control.git/171838


>> +             if (!have_read_execute_permissions(sb.buf))
>> +                     error("no read/execute permissions on '%s'\n", sb.buf);
>
> Don't you want to continue here upon error, after resetting sb? You just
> saw the directory is unreadble, so you know next file_exists() will fail
> before you try it.

Yes. I thought about that. I didn't do that because of the fact that I
had to do more than just resetting sb. The path variable has to be
updated as well. I had the choice of adding a level of indentation {},
duplicating the code, or just do a check I know before will fail.
There's probably something to say for each one of them. I'll probably
refactor that a bit more.


>> +             if (sb.len && sb.buf[sb.len - 1] != '/')
>> +                     strbuf_addch(&sb, '/');
>> +             strbuf_addstr(&sb, cmd);
>> +
>> +             if (file_exists(sb.buf)) {
>> +                     if (!have_read_execute_permissions(sb.buf))
>> +                             error("no read/execute permissions on '%s'\n",
>> +                                             sb.buf);
>> +                     else
>> +                             warn("file '%s' exists and permissions "
>> +                             "seem OK.\nIf this is a script, see if you "
>> +                             "have sufficient privileges to run the "
>> +                             "interpreter", sb.buf);
>
> Does "warn()" do the right thing for multi-line strings like this?

I don't know/remember. It seemed like a natural thing to do, but I'll find out.