Re: [PATCH v2] libfdt: fdt_path_offset_namelen: Reject empty path

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Oct 09, 2023 at 03:16:43PM +0100, Pierre-Clément Tosi wrote:
> Reject empty paths and negative lengths, according to the DT spec v0.4:
> 
>     The convention for specifying a device path is:
>         /node-name-1/node-name-2/node-name-N
> 
>     The path to the root node is /.
> 
> This prevents the access to path[0] from ever being out-of-bounds.
> 
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> ---
> v2
>   - allow the check to be optimized out when ASSUME_VALID_INPUT
>   - add test coverage for empty paths and negative size
>   - remove redundant part of the quote in the commit message
> ---
>  libfdt/fdt_ro.c     | 3 +++
>  tests/path_offset.c | 6 ++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
> index c4c520c..7567f52 100644
> --- a/libfdt/fdt_ro.c
> +++ b/libfdt/fdt_ro.c
> @@ -255,6 +255,9 @@ int fdt_path_offset_namelen(const void *fdt, const char *path, int namelen)
>  
>  	FDT_RO_PROBE(fdt);
>  
> +	if (!can_assume(VALID_INPUT) && namelen <= 0)
> +		return -FDT_ERR_BADPATH;
> +
>  	/* see if we have an alias */
>  	if (*path != '/') {
>  		const char *q = memchr(path, '/', end - p);
> diff --git a/tests/path_offset.c b/tests/path_offset.c
> index 8e657af..0193e61 100644
> --- a/tests/path_offset.c
> +++ b/tests/path_offset.c
> @@ -48,6 +48,9 @@ static void check_path_offset(void *fdt, const char *path, int offset)
>  	verbose_printf("Checking offset of \"%s\" is %d...\n", path, offset);
>  
>  	rc = fdt_path_offset(fdt, path);
> +	if (rc == offset)
> +		return;
> +

Since you're adding this test here...

>  	if (rc < 0)
>  		FAIL("fdt_path_offset(\"%s\") failed: %s",
>  		     path,  fdt_strerror(rc));

.. you shouldalso remove the (rc != offset) test which comes
immediately after this one.

> @@ -102,6 +105,7 @@ int main(int argc, char *argv[])
>  	check_path_offset(fdt, "/subnode@2/subsubnode", subsubnode2_offset2);
>  
>  	/* Test paths with extraneous separators */
> +	check_path_offset(fdt, "", -FDT_ERR_BADPATH);
>  	check_path_offset(fdt, "//", 0);
>  	check_path_offset(fdt, "///", 0);
>  	check_path_offset(fdt, "//subnode@1", subnode1_offset);
> @@ -110,6 +114,8 @@ int main(int argc, char *argv[])
>  	check_path_offset(fdt, "/subnode@2////subsubnode", subsubnode2_offset2);
>  
>  	/* Test fdt_path_offset_namelen() */
> +	check_path_offset_namelen(fdt, "/subnode@1", -1, -FDT_ERR_BADPATH);
> +	check_path_offset_namelen(fdt, "/subnode@1", 0, -FDT_ERR_BADPATH);
>  	check_path_offset_namelen(fdt, "/subnode@1", 1, 0);
>  	check_path_offset_namelen(fdt, "/subnode@1/subsubnode", 10, subnode1_offset);
>  	check_path_offset_namelen(fdt, "/subnode@1/subsubnode", 11, subnode1_offset);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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