From: Florian Weimer <fweimer@redhat.com>
To: David Malcolm <dmalcolm@redhat.com>
Cc: Szabolcs Nagy via Gcc <gcc@gcc.gnu.org>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha@sourceware.org, Mir Immad <mirimnan017@gmail.com>
Subject: Re: Adding file descriptor attribute(s) to gcc and glibc
Date: Wed, 13 Jul 2022 16:01:08 +0200 [thread overview]
Message-ID: <87tu7lyuvv.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <6460438cc9e634d0b5e40a1438038c9adce151bb.camel@redhat.com> (David Malcolm's message of "Wed, 13 Jul 2022 09:33:28 -0400")
* David Malcolm:
> On Wed, 2022-07-13 at 14:05 +0200, Florian Weimer wrote:
>> * Szabolcs Nagy via Gcc:
>
> [adding Immad back to the CC list]
>
>>
>> > to be honest, i'd expect interesting fd bugs to be
>> > dynamic and not easy to statically analyze.
>> > the use-after-unchecked-open maybe useful. i would
>> > not expect the access direction to catch many bugs.
>>
>> You might be right. But I think the annotations could help to catch
>> use-after-close errors.
>>
>> By the way, I think it would help us if we didn't have to special-
>> case
>> AT_FDCWD using inline wrappers.
>
> Florian: I confess I wasn't familiar with AT_FDCWD until I read your
> email and did a little reading a few minutes ago; it seems to be a
> "magic number" for an FD that has special meaning; on my system it has
> the value -100.
>
> GCC's current implementation of the various -Wanalyzer-fd-* warnings
> will track state for constant integer values as well as symbolic
> values; it doesn't have any special meanings for specific integer
> values. So e.g. it doesn't assume that 0, 1, and 2 have specific
> meaning or are opened with specific flags (the analysis doesn't
> necessarily begin its execution path at the start of "main", so there's
> no guarantee that the standard FDs have their standard meaning).
Ahh. It might be useful to detect close (-1) etc. as a form of
double-close, and ther AT_FDCWD is exceptional.
> Presumably if someone attempts
> close (AT_FDCWD);
> they'll get -1 and errno set to EBADFD, right?
Correct
> I don't think GCC's -fanalyzer needs to check for that.
Not sure …
> -fanalyzer's filedescriptor support doesn't yet have a concept of
> "directory filedescriptors". Should it? (similarly, it doesn't yet
> know about sockets)
>
> A possible way to annotate "openat":
>
> int openat(int dirfd, const char *pathname, int flags)
> __attr_fd_arg(1);
openat is not the most general interface in this regard. We have other
*at functions which accept an O_PATH descriptor (or maybe even a
different kind of non-directory descriptor) with pathname == "" and
AT_EMPTY_PATH. I'm not sure if modeling all this is beneficial.
Thanks,
Florian
next prev parent reply other threads:[~2022-07-13 14:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-12 17:31 [PATCH] filedescriptor attribute Immad Mir
2022-07-12 17:33 ` Mir Immad
2022-07-12 22:16 ` Adding file descriptor attribute(s) to gcc and glibc David Malcolm
2022-07-12 22:25 ` David Malcolm
2022-07-13 8:37 ` Szabolcs Nagy
2022-07-13 8:46 ` Andreas Schwab
2022-07-13 12:05 ` Florian Weimer
2022-07-13 13:33 ` David Malcolm
2022-07-13 14:01 ` Florian Weimer [this message]
2022-07-13 16:55 ` David Malcolm
2022-07-14 8:30 ` Szabolcs Nagy
2022-07-14 15:22 ` David Malcolm
2022-07-14 17:07 ` Paul Eggert
2022-07-13 16:56 ` Mir Immad
2022-07-13 19:29 ` David Malcolm
2022-07-13 12:57 ` David Malcolm
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