[PATCH] realpath: Do not copy result on failure (BZ #28815)

[Adhemerval Zanella]

On 24/01/2022 13:54, Siddhesh Poyarekar via Libc-alpha wrote:
> On failure, the contents of the resolved buffer passed in by the caller
> to realpath are undefined.  Do not copy any partial resolution to the
> buffer and also do not test resolved contents in test-canon.c.
> 
> Resolves: BZ #28815
> 
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  stdlib/canonicalize.c | 4 ++--
>  stdlib/test-canon.c   | 4 +++-
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c
> index 6caed9e70e..6237a41d42 100644
> --- a/stdlib/canonicalize.c
> +++ b/stdlib/canonicalize.c
> @@ -400,11 +400,11 @@ realpath_stk (const char *name, char *resolved,
>  
>  error:
>    *dest++ = '\0';
> -  if (resolved != NULL)
> +  if (!failed && resolved != NULL)
>      {
>        if (dest - rname <= get_path_max ())
>  	rname = strcpy (resolved, rname);
> -      else if (!failed)
> +      else
>  	{
>  	  failed = true;
>  	  __set_errno (ENAMETOOLONG);
> diff --git a/stdlib/test-canon.c b/stdlib/test-canon.c
> index 185ccf4f48..2ad1218749 100644
> --- a/stdlib/test-canon.c
> +++ b/stdlib/test-canon.c
> @@ -174,7 +174,9 @@ do_test (int argc, char ** argv)
>  	  continue;
>  	}
>  
> -      if (!check_path (buf, tests[i].out ? tests[i].out : tests[i].resolved))
> +      /* Only on success verify that buf contains the result too.  */
> +      if (result != NULL
> +	  && !check_path (buf, tests[i].out ? tests[i].out : tests[i].resolved))
>  	{
>  	  printf ("%s: flunked test %d (expected resolved `%s', got `%s')\n",
>  		  argv[0], i, tests[i].out ? tests[i].out : tests[i].resolved,