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Message-ID: <20190701141202.GQ1506@brightrain.aerifal.cx>
Date: Mon, 1 Jul 2019 10:12:02 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] fix deadlock in synccall after threaded fork
On Sun, Jun 30, 2019 at 10:44:28PM -0500, Samuel Holland wrote:
> synccall may be called by AS-safe functions such as setuid/setgid after
> fork. although fork() resets libc.threads_minus_one, causing synccall to
> take the single-threaded path, synccall still takes the thread list
> lock. This lock may be held by another thread if for example fork()
> races with pthread_create(). After fork(), the value of the lock is
> meaningless, so clear it.
> ---
> src/process/fork.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/src/process/fork.c b/src/process/fork.c
> index 11286ef4..fb42478a 100644
> --- a/src/process/fork.c
> +++ b/src/process/fork.c
> @@ -28,6 +28,7 @@ pid_t fork(void)
> self->robust_list.off = 0;
> self->robust_list.pending = 0;
> self->next = self->prev = self;
> + __thread_list_lock = 0;
> libc.threads_minus_1 = 0;
> }
> __restore_sigs(&set);
> --
> 2.21.0
Thanks! Committing this with a maintainer's note referencing the
commits that caused the regression and a further remark on why it's
safe/correct to make this change.
Rich
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