Re: [Xen-devel] [PATCH] tools: libxl: NULL terminate partially constructed hex string

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Feb 16, 2016 at 11:18:20AM +0000, Ian Campbell wrote:
> Coverity (correctly) complains that the strncpy(p, "0x", 2) will not
> null terminate p.
> 
> Although we can see that in the rest of the function p will
> definitely be NULL terminated by the time it is complete there is no
> harm in passing 3 to the strncpy and allowing it to NULL terminate to
> placate Coverity. We know this is safe because the allocation to hold
> the string includes a "+3" for the 0x and the terminating NULL.
> 
> Compile tested only.
> 
> CID: 1198708
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> ---
> I flip-flopped on just telling Coverity this was a false +ve, but
> mainly landed on this course of action because the issue was marked as
> "fix required" by Ian J in the coverity interface (it was also marked
> "insignificant" FWIW).
> ---
>  tools/libxl/libxl_utils.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
> index e42422a..672d3f8 100644
> --- a/tools/libxl/libxl_utils.c
> +++ b/tools/libxl/libxl_utils.c
> @@ -780,7 +780,7 @@ char *libxl_bitmap_to_hex_string(libxl_ctx *ctx, const 
> libxl_bitmap *bitmap)
>      int i = bitmap->size;
>      char *p = libxl__zalloc(NOGC, bitmap->size * 2 + 3);
>      char *q = p;
> -    strncpy(p, "0x", 2);
> +    strncpy(p, "0x", 3);
>      p += 2;
>      while(--i >= 0) {
>          sprintf(p, "%02x", bitmap->map[i]);
> -- 
> 2.1.4
> 

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