[PATCH, RFC] - xfsprogs: pad ustat struct for mount check to avoid corruption

[Eric Sandeen]

Linux kernels (at least up until 2.6.27) are lacking compat sys_ustat
handlers on some platforms (notably PPC) so that if called from 32 bits
on a 64-bit kernel, the kernel will copy out too much (32 bytes onto a
20-byte structure):

[root at xero xfstests]# xfs_logprint /dev/loop0
xfs_logprint:
*** stack smashing detected ***: xfs_logprint terminated
Aborted

This will be fixed upstream, but for the benefit of older kernels we
may want to guard against this by padding the structure we pass into
the syscall.   We don't care about the values anyway, just the return
value.

Signed-off-by: Eric Sandeen <sandeen at sandeen.net>
---

Index: xfs-cmds/xfsprogs/libxfs/linux.c
===================================================================
--- xfs-cmds.orig/xfsprogs/libxfs/linux.c
+++ xfs-cmds/xfsprogs/libxfs/linux.c
@@ -49,7 +49,8 @@ static int max_block_alignment;
 int
 platform_check_ismounted(char *name, char *block, struct stat64 *s, int verbose)
 {
-	struct ustat	ust;
+	/* Pad ust; pre-2.6.28 linux copies out too much in 32bit compat mode */
+	struct ustat	ust[2];
 	struct stat64	st;
 
 	if (!s) {
@@ -60,7 +61,7 @@ platform_check_ismounted(char *name, cha
 		s = &st;
 	}
 
-	if (ustat(s->st_rdev, &ust) >= 0) {
+	if (ustat(s->st_rdev, ust) >= 0) {
 		if (verbose)
 			fprintf(stderr,
 				_("%s: %s contains a mounted filesystem\n"),