[dpdk-stable] [dpdk-dev] [PATCH] cfgfile: avoid stack buffer underflow

[Bruce Richardson]

On Wed, Jul 01, 2020 at 08:05:58PM -0700, Stephen Hemminger wrote:
> If cfgfile is give a line with comment character at the start
> of the line, it will dereference outside of the buffer.
> 
> Detected with address sanitizer:
> 
> SUMMARY: AddressSanitizer: stack-buffer-underflow lib/librte_cfgfile/rte_cfgfile.c:194 in rte_cfgfile_load_with_params
> Shadow bytes around the buggy address:
>   0x200fff79f6a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f6b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f6c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f6d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f6e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> =>0x200fff79f6f0: 00 00 00 00 f1 f1 f1[f1]00 00 00 00 00 00 00 00
>   0x200fff79f700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f710: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x200fff79f720: 04 f2 f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00 00
>   0x200fff79f730: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2
>   0x200fff79f740: f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00
> Shadow byte legend (one shadow byte represents 8 application bytes):
>   Addressable:           00
>   Partially addressable: 01 02 03 04 05 06 07
>   Heap left redzone:       fa
>   Freed heap region:       fd
>   Stack left redzone:      f1
>   Stack mid redzone:       f2
>   Stack right redzone:     f3
>   Stack after return:      f5
>   Stack use after scope:   f8
>   Global redzone:          f9
>   Global init order:       f6
>   Poisoned by user:        f7
>   Container overflow:      fc
>   Array cookie:            ac
>   Intra object redzone:    bb
>   ASan internal:           fe
>   Left alloca redzone:     ca
>   Right alloca redzone:    cb
> ==2189==ABORTING
> 
> Fixes: a6a47ac9c2c9 ("cfgfile: rework load function")
> Cc: jacekx.piasecki at intel.com
> CC: stable at dpdk.org
> Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
> ---
>  lib/librte_cfgfile/rte_cfgfile.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_cfgfile/rte_cfgfile.c b/lib/librte_cfgfile/rte_cfgfile.c
> index 714717dd9007..160d78826e7c 100644
> --- a/lib/librte_cfgfile/rte_cfgfile.c
> +++ b/lib/librte_cfgfile/rte_cfgfile.c
> @@ -191,7 +191,8 @@ rte_cfgfile_load_with_params(const char *filename, int flags,
>  		}
>  		/* skip parsing if comment character found */
>  		pos = memchr(buffer, params->comment_character, len);
> -		if (pos != NULL && (*(pos-1) != '\\')) {
> +		if (pos != NULL &&
> +		    (pos == buffer || *(pos-1) != '\\')) {
>  			*pos = '\0';
>  			len = pos -  buffer;
>  		}
> -- 

Good catch by the tool.

Reviewed-by: Bruce Richardson <bruce.richardson at intel.com>