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Date: Fri, 10 Nov 2017 18:31:34 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] save/restore errno around pthread_atfork handlers
On Fri, Nov 10, 2017 at 02:58:29PM -0600, Bobby Bingham wrote:
> If the syscall fails, errno must be preserved for the caller. There's no
> guarantee that the handlers registered with pthread_atfork won't clobber
> errno.
> ---
> src/process/fork.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/src/process/fork.c b/src/process/fork.c
> index b96f0024..6602eafc 100644
> --- a/src/process/fork.c
> +++ b/src/process/fork.c
> @@ -15,6 +15,7 @@ pid_t fork(void)
> {
> pid_t ret;
> sigset_t set;
> + int olderr;
> __fork_handler(-1);
> __block_all_sigs(&set);
> #ifdef SYS_fork
> @@ -30,6 +31,10 @@ pid_t fork(void)
> libc.threads_minus_1 = 0;
> }
> __restore_sigs(&set);
> +
> + olderr = errno;
> __fork_handler(!ret);
> + errno = olderr;
> +
> return ret;
> }
> --
> 2.15.0
I think the patch as written is incorrect, because it can set errno to
0 after application code in the atfork handler set it to something
nonzero; doing so is non-conforming.
It would be possible to special-case to avoid this, but it probably
makes more sense to just call SYS_fork/SYS_clone with __syscall rather
than syscall, then return __syscall_ret(ret) instead of return ret.
Does that sound correct?
Rich
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