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Message-ID: <20210125144236.GV23432@brightrain.aerifal.cx>
Date: Mon, 25 Jan 2021 09:42:36 -0500
From: Rich Felker <dalias@...c.org>
To: Bruno Haible <bruno@...sp.org>
Cc: musl@...ts.openwall.com
Subject: Re: insufficient checking in
posix_spawn_file_actions_add{open,dup2}
On Mon, Jan 25, 2021 at 09:31:50AM +0100, Bruno Haible wrote:
> Hi,
>
> POSIX [1][2] says about the functions
> posix_spawn_file_actions_addopen
> posix_spawn_file_actions_adddup2
>
> The function "shall fail if:
> [EBADF]
> The value specified by fildes is negative or greater than or equal to {OPEN_MAX}."
>
> However, in musl libc 1.2.2, these two test programs exit with status 2:
> ========================================================================
> #include <spawn.h>
> #include <fcntl.h>
> int main ()
> {
> posix_spawn_file_actions_t actions;
> if (posix_spawn_file_actions_init (&actions) != 0)
> return 1;
> if (posix_spawn_file_actions_addopen (&actions, 10000000, "foo", 0, O_RDONLY)
> == 0)
> return 2;
> return 0;
> }
> ========================================================================
> #include <spawn.h>
> int main ()
> {
> posix_spawn_file_actions_t actions;
> if (posix_spawn_file_actions_init (&actions) != 0)
> return 1;
> if (posix_spawn_file_actions_adddup2 (&actions, 10000000, 2) == 0)
> return 2;
> return 0;
> }
> ========================================================================
>
> sysconf (_SC_OPEN_MAX) is 1024, on that system.
>
> Best regards,
>
> Bruno
>
> [1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_spawn_file_actions_addopen.html
> [2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_spawn_file_actions_adddup2.html
Thanks. I think I was vaguely aware of this, but misremembered
https://www.austingroupbugs.net/view.php?id=418 as dropping the
requirement (which is rather odious, especially if a file action for
changing rlimit were ever to be added) rather than just removing it
for close.
With that said, is there any normative text that {OPEN_MAX} in the
spec indicates a requirement to honor a dynamic max
sysconf(_SC_OPEN_MAX)? As written, the "shall fail" seems to apply
just on systems where OPEN_MAX is defined; sysconf isn't referenced. I
would very much prefer not to have to enforce such a max here since
it's hostile to future extensibility and wastes a syscall in an
operation that should not require one.
In any case negative values should be checked.
Rich
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