Re: [xfsprogs PATCH v2 1/3] xfs_io: fix compiler warnings in getfsmap code

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Dec 05, 2017 at 04:56:49PM -0700, Ross Zwisler wrote:
> I recently upgraded my compiler from
> 	gcc (GCC) 6.4.1 20170727 (Red Hat 6.4.1-1)
> to
> 	gcc (GCC) 7.2.1 20170915 (Red Hat 7.2.1-2)
> and started getting a bunch of compiler warnings in io/fsmap.c:
> 
>   fsmap.c: In function ‘fsmap_f’:
>   fsmap.c:228:40: warning: ‘%lld’ directive output may be truncated writing
>   between 1 and 17 bytes into a region of size between 12 and 28
>   [-Wformat-truncation=]
>      snprintf(bbuf, sizeof(bbuf), "[%lld..%lld]:",
>   ^~~~
>   fsmap.c:228:32: note: directive argument in the range [0, 36028797018963967]
>      snprintf(bbuf, sizeof(bbuf), "[%lld..%lld]:",
>   ^~~~~~~~~~~~~~~
>   fsmap.c:228:3: note: ‘snprintf’ output between 8 and 40 bytes into a
>   destination of size 32
>      snprintf(bbuf, sizeof(bbuf), "[%lld..%lld]:",
>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   (long long)BTOBBT(p->fmr_physical),
>   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   (long long)BTOBBT(p->fmr_physical + p->fmr_length - 1));
>   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The issue is that 'bbuf' is only defined to be 32 characters wide, but each
> signed long long can potentially print as many as 19 characters
> (9223372036854775807 is the max value).  The format we're using for bbuf is
> "[%lld..%lld]:" which has 2 signed long longs plus 6 other characters
> "[..]:\0", which means it's possible we'll print up to 44 characters,
> overflowing our 32 char buffer.
> 
> Fix this by bumping all the buffer sizes in dump_map_verbose() to 64
> characters.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Darrick J. Wong <darrick.wong@oracle.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

> Fixes: 3fcab549a234 ("xfs_io: support the new getfsmap ioctl")
> ---
>  io/fsmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/io/fsmap.c b/io/fsmap.c
> index 448fb535..3d8a6700 100644
> --- a/io/fsmap.c
> +++ b/io/fsmap.c
> @@ -184,8 +184,8 @@ dump_map_verbose(
>  	off64_t			agoff, bperag;
>  	int			foff_w, boff_w, aoff_w, tot_w, agno_w, own_w;
>  	int			nr_w, dev_w;
> -	char			rbuf[32], bbuf[32], abuf[32], obuf[32];
> -	char			nbuf[32], dbuf[32], gbuf[32];
> +	char			rbuf[64], bbuf[64], abuf[64], obuf[64];
> +	char			nbuf[64], dbuf[64], gbuf[64];
>  	char			owner[OWNER_BUF_SZ];
>  	int			sunit, swidth;
>  	int			flg = 0;
> -- 
> 2.14.3
> 
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