From 0717c1cdfeaedc98df8af97b5ab110830e176a5b Mon Sep 17 00:00:00 2001
From: Gao Xiang <hsiangkao@redhat.com>
Date: Thu, 3 Feb 2022 12:42:30 -0500
Subject: [PATCH 2/2] xfsdump: intercept bind mount targets

It's a bit strange pointing at some non-root bind mount target and
then actually dumping from the actual root dir instead.

Therefore, instead of searching for the root dir of the filesystem,
just intercept all bind mount targets by checking whose ino # of
".." is itself with getdents.

Fixes: 25195ebf107d ("xfsdump: handle bind mount targets")
Cc: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
[sandeen: add explanatory comment to new function]
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---

Index: xfsdump-3.1.8/dump/content.c
===================================================================
--- xfsdump-3.1.8.orig/dump/content.c
+++ xfsdump-3.1.8/dump/content.c
@@ -511,6 +511,60 @@ static bool_t create_inv_session(
 		ix_t subtreecnt,
 		size_t strmix);
 
+/*
+ * Verify that we are asked to dump from the root of the filesystem;
+ * test this by checking whether the inode number we've been given matches
+ * the inode number for this directory's ".."
+ */
+static bool_t
+check_rootdir(int fd,
+	      xfs_ino_t ino)
+{
+	struct dirent	*gdp;
+	size_t		gdsz;
+	bool_t		found = BOOL_FALSE;
+
+	gdsz = sizeof(struct dirent) + NAME_MAX + 1;
+	if (gdsz < GETDENTSBUF_SZ_MIN)
+		gdsz = GETDENTSBUF_SZ_MIN;
+	gdp = (struct dirent *)calloc(1, gdsz);
+	assert(gdp);
+
+	while (1) {
+		struct dirent *p;
+		int nread;
+
+		nread = getdents_wrap(fd, (char *)gdp, gdsz);
+		/*
+		 * negative count indicates something very bad happened;
+		 * try to gracefully end this dir.
+		 */
+		if (nread < 0) {
+			mlog(MLOG_NORMAL | MLOG_WARNING,
+_("unable to read dirents for directory ino %llu: %s\n"),
+			      ino, strerror(errno));
+			break;
+		}
+
+		/* no more directory entries: break; */
+		if (!nread)
+			break;
+
+		for (p = gdp; nread > 0;
+		     nread -= (int)p->d_reclen,
+		     assert(nread >= 0),
+		     p = (struct dirent *)((char *)p + p->d_reclen)) {
+			if (!strcmp(p->d_name, "..")) {
+				if (p->d_ino == ino)
+					found = BOOL_TRUE;
+				break;
+			}
+		}
+	}
+	free(gdp);
+	return found;
+}
+
 bool_t
 content_init( int argc,
 	      char *argv[ ],
@@ -1394,6 +1448,14 @@ baseuuidbypass:
 			      mntpnt );
 			return BOOL_FALSE;
 		}
+
+		if (!check_rootdir(sc_fsfd, rootstat.st_ino)) {
+			mlog(MLOG_ERROR,
+_("%s is not the root of the filesystem (bind mount?) - use primary mountpoint\n"),
+			     mntpnt);
+			return BOOL_FALSE;
+		}
+
 		sc_rootxfsstatp =
 			( xfs_bstat_t * )calloc( 1, sizeof( xfs_bstat_t ));
 		assert( sc_rootxfsstatp );