[PATCH] libdwfl: fix DEREF_OF_NULL.EX in dwfl_segment_report_module.c

[Mark Wielaard]

Hi Anton,

On Sat, Feb 01, 2025 at 02:10:03AM +0300, Anton Moryakov wrote:
> Report of the static analyzer:
> After having been assigned to a NULL value at
> dwfl_segment_report_module.c:187, pointer 'retval' is
> dereferenced at dwfl_segment_report_module.c:195 by
> calling function 'strcmp'. (CWE476)

These line numbers seem off. Which version of the file are you
checking against?

> Corrections explained:
> When processing file notes, the code could dereference
> a NULL pointer if 'retval' was not initialized. This patch
> adds a check to ensure 'retval' is not NULL before using it
> in strcmp.
> 
> The fix ensures that the function safely handles cases where
> 'retval' is NULL, avoiding potential crashes.

Isn't this the same as we discussed before?
https://inbox.sourceware.org/elfutils-devel/fafbecf35ed2545ecd161dde1c5bbb4c1b4961b6.camel@klomp.org/
and
https://inbox.sourceware.org/elfutils-devel/20240702111528.GA29242@gnu.wildebeest.org/

Was the analyzis in the above messages incorrect?

Thanks,

Mark

> Triggers found by static analyzer Svace.
> 
> Signed-off-by: Anton Moryakov <ant.v.moryakov at gmail.com>
> 
> ---
>  libdwfl/dwfl_segment_report_module.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
> index 32f44af8..565884f0 100644
> --- a/libdwfl/dwfl_segment_report_module.c
> +++ b/libdwfl/dwfl_segment_report_module.c
> @@ -205,8 +205,11 @@ handle_file_note (GElf_Addr module_start, GElf_Addr module_end,
>  	return NULL;
>        if (mix == firstix)
>  	retval = fptr;
> -      if (firstix < mix && mix <= lastix && strcmp (fptr, retval) != 0)
> -	return NULL;
> +      if (firstix < mix && mix <= lastix)
> +      {
> +        if (retval == NULL || strcmp(fptr, retval) != 0)
> +          return NULL;
> +      }
>        fptr = fnext + 1;
>      }
>    return retval;
> -- 
> 2.30.2
>