[PATCH 5.10.y] xfs: bound da-node entry count against the correct geometry

[Sasha Levin <sashal@kernel.org>]

From: Aldo Ariel Panzardo <qwe.aldo@gmail.com>

[ Upstream commit 3df5e5aaa3bc0913236c48ab29b7df3a785aa29f ]

xfs_da3_node_verify() bounds the node entry count against the larger of
the directory and attribute geometries because, as a buffer verifier, it
cannot tell whether the block belongs to the directory or the attribute
tree. When the directory block size exceeds the fs block size (e.g.
mkfs.xfs -n size=64k -b size=4k), an attribute node buffer is a single fs
block that holds only m_attr_geo->node_ents entries, yet a crafted attr
node may claim a count up to m_dir_geo->node_ents and still pass the
verifier.

xfs_da3_node_lookup_int() then indexes btree[] up to that count during
its binary search -- an out-of-bounds read via getxattr/listxattr on a
mounted crafted image.

The buffer verifier is the wrong place to tighten this: it has no fork
context, and the transaction-less read path used by getxattr does not run
xfs_da3_node_set_type() either. xfs_da3_node_lookup_int(), on the other
hand, always runs on that path and holds args->geo, the geometry of the
fork actually being searched. Bound the entry count against
args->geo->node_ents there, before walking the entries.

Fixes: 7ab610f9e0f1 ("xfs: move node entry counts to xfs_da_geometry")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
[ sashal: Omitted the xfs_da_mark_sick() call because the helper is unavailable. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/xfs/libxfs/xfs_da_btree.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
index 08871fa84419b..8300d67ae007f 100644
--- a/fs/xfs/libxfs/xfs_da_btree.c
+++ b/fs/xfs/libxfs/xfs_da_btree.c
@@ -1658,6 +1658,19 @@ xfs_da3_node_lookup_int(
 		} else
 			expected_level--;
 
+		/*
+		 * The node verifier cannot tell whether this block belongs to
+		 * the directory or the attribute tree, so it only bounds the
+		 * entry count against the larger of the two geometries.  Here
+		 * args->geo is the geometry of the fork we are actually
+		 * searching, so reject a count that would walk btree[] off the
+		 * end of this node buffer.
+		 */
+		if (nodehdr.count > args->geo->node_ents) {
+			xfs_buf_mark_corrupt(blk->bp);
+			return -EFSCORRUPTED;
+		}
+
 		max = nodehdr.count;
 		blk->hashval = be32_to_cpu(btree[max - 1].hashval);
 
-- 
2.53.0