Re: [PATCH v1 1/2] tools: mkimage: fix get_basename crash on paths with dotted directories

[Marek Vasut <marek.vasut@mailbox.org>]

On 5/21/26 4:34 AM, Aristo Chen wrote:
> The get_basename() helper in tools/fit_image.c searches the entire input
> path for the last '/' and the last '.' independently. When the last '.'
> falls at an offset earlier than the last '/' (for example "./mydt",
> "a.b/c", or "sub.d/leaf"), 'end' points before 'start' and the computed
> length is negative. The subsequent size check uses signed comparison so
> the negative value passes through unchanged, and memcpy() is then called
> with that length implicitly cast to size_t, which segfaults.
> 
> Restrict the dot search to the substring that follows the last slash so
> that only an extension in the filename component can become the end of
> the basename. This matches the function's stated intent of stripping an
> extension from the leaf, and keeps the existing behaviour for typical
> inputs such as "arch/arm/dts/foo.dtb".
> 
> Reproducer that previously segfaulted and now produces a valid image:
> 
>    echo dummy > kernel.bin
>    echo dummy > ./mydt
>    ./tools/mkimage -f auto -A arm -O linux -T kernel -C none \
>                    -a 0x80000000 -e 0x80000000 -n test \
>                    -d kernel.bin -b ./mydt out.itb
> 
> Signed-off-by: Aristo Chen <aristo.chen@canonical.com>
> ---
>   tools/fit_image.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/fit_image.c b/tools/fit_image.c
> index 1dbc14c63e4..6c129117297 100644
> --- a/tools/fit_image.c
> +++ b/tools/fit_image.c
> @@ -265,8 +265,14 @@ static void get_basename(char *str, int size, const char *fname)
>   	 */
>   	p = strrchr(fname, '/');
>   	start = p ? p + 1 : fname;
> -	p = strrchr(fname, '.');
> -	end = p ? p : fname + strlen(fname);
> +	/*
> +	 * Search for the extension dot only within the basename. Searching
> +	 * the whole path would let a dot in the directory part (for example
> +	 * "./mydt" or "a.b/c") place 'end' before 'start' and produce a
> +	 * negative length, which the size check below does not catch.
> +	 */
> +	p = strrchr(start, '.');
> +	end = p ? p : start + strlen(start);
>   	len = end - start;
>   	if (len >= size)
>   		len = size - 1;

Why not call basename(3) directly in here ? Why reimplement it ?