[PATCH] xfs_repair: detect null buf passed to duration

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

gcc 12.2 with ubsan and fortify turned on complains about this:

In file included from /usr/include/stdio.h:906,
                 from ../include/platform_defs.h:9,
                 from ../include/libxfs.h:16,
                 from progress.c:3:
In function ‘sprintf’,
    inlined from ‘duration’ at progress.c:443:4:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:30:10: error: null destination pointer [-Werror=format-overflow=]
   30 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   31 |                                   __glibc_objsize (__s), __fmt,
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   32 |                                   __va_arg_pack ());
      |                                   ~~~~~~~~~~~~~~~~~

I think this is a false negative since all callers are careful not to
pass in a null pointer.  Unfortunately the compiler cannot detect that
since this isn't a static function and complains.  Fix this by adding an
explicit null check.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 repair/progress.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/repair/progress.c b/repair/progress.c
index 084afa63c121..e13494e0ed23 100644
--- a/repair/progress.c
+++ b/repair/progress.c
@@ -435,6 +435,9 @@ duration(time_t length, char *buf)
 	int seconds;
 	char temp[128];
 
+	if (!buf)
+		return NULL;
+
 	*buf = '\0';
 	weeks = days = hours = minutes = seconds = sum = 0;
 	if (length >= ONEWEEK) {