Re: [musl] [PATCH] dynlink: fix get_lfs64() with posix_fallocate64

[Rich Felker <dalias@libc.org>]

On Fri, May 10, 2024 at 06:01:58PM +0200, Florian Ziesche wrote:
> Hi,
> 
> this patch increases the buffer size by one in get_lfs64() so that it
> works with posix_fallocate64.
> "posix_fallocate64" is 17 characters long, so 16 is one too short.
> 
> Simplified example:
> before: https://compiler-explorer.com/z/4qcPhcaWr
> after: https://compiler-explorer.com/z/scGvhddKW
> 
> ---
> diff --git a/ldso/dynlink.c b/ldso/dynlink.c
> index 42687da2..8707ae1c 100644
> --- a/ldso/dynlink.c
> +++ b/ldso/dynlink.c
> @@ -363,7 +363,7 @@ static struct symdef get_lfs64(const char *name)
>          "stat\0statfs\0statvfs\0tmpfile\0truncate\0versionsort\0"
>          "__fxstat\0__fxstatat\0__lxstat\0__xstat\0";
>      size_t l;
> -    char buf[16];
> +    char buf[17];
>      for (l=0; name[l]; l++) {
>          if (l >= sizeof buf) goto nomatch;
>          buf[l] = name[l];

Thanks for catching this. I questioned whether the 17 is sufficient,
but indeed the buffer is never nul terminated except when removing the
64, so it should be ok.

I think I'll apply your patch as a direct fix, but the whole copying
operation is unnecessary and I'll probably remove it. It works just as
well to strncmp and pass p instead of buf to find_sym, so that a
mutable copy of the name to lookup is never needed.

Rich