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Message-ID: <20210113143809.608ea269@ncopa-desktop.lan>
Date: Wed, 13 Jan 2021 14:38:09 +0100
From: Natanael Copa <ncopa@...inelinux.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] make realpath replace leading // with a single /
On Wed, 13 Jan 2021 14:28:35 +0100
Natanael Copa <ncopa@...inelinux.org> wrote:
> On some systems a leading double slash may have special meaning, so
> POSIX[1] says that "If a pathname begins with two successive <slash>
> characters, the first component following the leading <slash> characters
> may be interpreted in an implementation-defined manner"
>
> While current musl implementation is technically correct, most other
> systems' (at least GNU libc, freebsd, openbsd, netbsd macOS)
> implementations will replace a leading // with a single /. Make musl
> do the same to avoid surprises.
>
> [1]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
> ---
> src/misc/realpath.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/src/misc/realpath.c b/src/misc/realpath.c
> index db8b74dc..414b4741 100644
> --- a/src/misc/realpath.c
> +++ b/src/misc/realpath.c
> @@ -46,9 +46,6 @@ restart:
> q=0;
> output[q++] = '/';
> p++;
> - /* Initial // is special. */
> - if (stack[p] == '/' && stack[p+1] != '/')
> - output[q++] = '/';
> continue;
> }
>
This fixes gettext's (gnulib) testsuite, which tests if realpath("//",
NULL) return "/" and fails if it doesn't.
I ran this testcase on multiple systems:
#include <stdio.h>
#include <stdlib.h>
int main() {
printf("%s\n", realpath("//", NULL));
return 0;
}
musl 1.1.24: /
ubuntu 20.03: /
macOS Big Sur: /
OpenBSD 6.8: /
FreeBSD 12.2: /
NetBSD 9.1: /
musl (current) //
I don't know why this behavior was introduced in musl, but I think
this only adds meaningless friction to downstream users.
-nc
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