From a547152d47909aba27336a1d1d42fccf96262476 Mon Sep 17 00:00:00 2001
From: Eric Sandeen <sandeen@sandeen.net>
Date: Wed, 25 Jan 2017 20:02:43 -0600
Subject: [PATCH] libxfs: sanitize agcount on load

Before we get into libxfs_initialize_perag and try to blindly
allocate a perag struct for every (possibly corrupted number of)
AGs, see if we can read the last one.  If not, assume it's corrupt,
and load only the first AG.

Do this only for an arbitrarily high-ish agcount, so that normal-ish
geometry on a possibly truncated file or device will still do
its best to make all readable AGs available.

Set xfs_db's exitcode to 1 if this happens.

Also teach metadump to detect this and exit appropriately if
truncated, as it resets exitcode to 0 for its own purposes internally.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---
 db/init.c     |  6 ++++++
 db/metadump.c | 10 ++++++++++
 libxfs/init.c | 23 +++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/db/init.c b/db/init.c
index ec1e274c4..59fc3e0c3 100644
--- a/db/init.c
+++ b/db/init.c
@@ -58,6 +58,7 @@ init(
 {
 	struct xfs_sb	*sbp;
 	struct xfs_buf	*bp;
+	unsigned int	agcount;
 	int		c;
 
 	setlocale(LC_ALL, "");
@@ -148,6 +149,7 @@ init(
 		}
 	}
 
+	agcount = sbp->sb_agcount;
 	mp = libxfs_mount(&xmount, sbp, x.ddev, x.logdev, x.rtdev,
 			  LIBXFS_MOUNT_DEBUGGER);
 	if (!mp) {
@@ -159,6 +161,10 @@ init(
 	mp->m_log = &xlog;
 	blkbb = 1 << mp->m_blkbb_log;
 
+	/* Did we limit a broken agcount in libxfs_mount? */
+	if (sbp->sb_agcount != agcount)
+		exitcode = 1;
+
 	/*
 	 * xfs_check needs corrected incore superblock values
 	 */
diff --git a/db/metadump.c b/db/metadump.c
index 1ba6b3853..38519f1be 100644
--- a/db/metadump.c
+++ b/db/metadump.c
@@ -2760,6 +2760,16 @@ metadump_f(
 		return 0;
 	}
 
+	/*
+	 * on load, we sanity-checked agcount and possibly set to 1
+	 * if it was corrupted and large.
+	 */
+	if (mp->m_sb.sb_agcount == 1 &&
+	    XFS_MAX_DBLOCKS(&mp->m_sb) < mp->m_sb.sb_dblocks) {
+		print_warning("truncated agcount, giving up");
+		return 0;
+	}
+
 	while ((c = getopt(argc, argv, "aegm:ow")) != EOF) {
 		switch (c) {
 			case 'a':
diff --git a/libxfs/init.c b/libxfs/init.c
index a08575a75..85e0d1591 100644
--- a/libxfs/init.c
+++ b/libxfs/init.c
@@ -817,6 +817,29 @@ libxfs_mount(
 			return NULL;
 	}
 
+	/*
+	 * libxfs_initialize_perag will allocate a perag structure for each ag.
+	 * If agcount is corrupted and insanely high, this will OOM the box.
+	 * If the agount seems (arbitrarily) high, try to read what would be
+	 * the last AG, and if that fails for a relatively high agcount, just
+	 * read the first one and let the user know to check the geometry.
+	 */
+	if (sbp->sb_agcount > 1000000) {
+		bp = libxfs_readbuf(mp->m_dev,
+				XFS_AG_DADDR(mp, sbp->sb_agcount - 1, 0), 1,
+				!(flags & LIBXFS_MOUNT_DEBUGGER), NULL);
+		if (bp->b_error) {
+			fprintf(stderr, _("%s: read of AG %u failed\n"),
+						progname, sbp->sb_agcount);
+			if (!(flags & LIBXFS_MOUNT_DEBUGGER))
+				return NULL;
+			fprintf(stderr, _("%s: limiting reads to AG 0\n"),
+								progname);
+			sbp->sb_agcount = 1;
+		}
+		libxfs_putbuf(bp);
+	}
+
 	error = libxfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
 	if (error) {
 		fprintf(stderr, _("%s: perag init failed\n"),
-- 
2.47.2