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

Dave Chinner
2017-12-06T00:27:46Z

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>
> Fixes: 3fcab549a234 ("xfs_io: support the new getfsmap ioctl")

FYI, I posted a fix for this weeks ago. I think Eric has already
picked it up, but it hasn't been pushed out into the for-next branch
yet.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com