[PATCH v2] xfs: bound inode fork length against the fork size during log recovery

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

xlog_recover_inode_commit_pass2() copies an inode log item's data/attr
fork region into the inode buffer using the on-log region length without
bounding it against the fork capacity, e.g.:

	len = item->ri_buf[2].iov_len;
	memcpy(XFS_DFORK_DPTR(dip), src, len);

The only guard is an ASSERT, which is a no-op on production kernels
(CONFIG_XFS_DEBUG off), and xfs_dinode_verify() runs only after the copy.
A crafted image with a dirty log can therefore drive a heap out-of-bounds
write at mount time. The XFS_ILOG_DBROOT sibling already passes
XFS_DFORK_DSIZE as a bound; the DDATA/DEXT and ADATA/AEXT memcpy paths
did not.

Bound each logged fork region against the destination fork size before
copying it, and reject the log item with -EFSCORRUPTED when it does not
fit. Because the recovered inode is only verified after the fork data has
been copied in, the checks are done up front, before any memcpy into the
on-disk inode.

Fixes: 658fa68b6f34 ("xfs: refactor log recovery inode item dispatch for pass2 commit functions")
Cc: <stable@vger.kernel.org> # v5.8
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
v2: cc stable # v5.8 (per Darrick).  Move both fork-length checks to the
    top of the fork-copy block, before any memcpy into the on-disk
    inode, and drop the now-redundant ASSERT.

 fs/xfs/xfs_inode_item_recover.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_inode_item_recover.c b/fs/xfs/xfs_inode_item_recover.c
index 169a8fe3bf0a..6c7dd7dd7032 100644
--- a/fs/xfs/xfs_inode_item_recover.c
+++ b/fs/xfs/xfs_inode_item_recover.c
@@ -507,6 +507,25 @@ xlog_recover_inode_commit_pass2(
 	ASSERT(!(fields & XFS_ILOG_DFORK) ||
 	       (len == xlog_calc_iovec_len(in_f->ilf_dsize)));
 
+	/*
+	 * The recovered inode is verified only after the fork data has been
+	 * copied into it, so bound each logged fork region against the size of
+	 * its fork now, before the memcpy below can overrun the on-disk inode.
+	 * The DBROOT/ABROOT cases already bound their copies against the fork
+	 * size.
+	 */
+	if ((fields & (XFS_ILOG_DDATA | XFS_ILOG_DEXT)) &&
+	    item->ri_buf[2].iov_len > XFS_DFORK_DSIZE(dip, mp)) {
+		error = -EFSCORRUPTED;
+		goto out_release;
+	}
+	if ((fields & (XFS_ILOG_ADATA | XFS_ILOG_AEXT)) &&
+	    item->ri_buf[(fields & XFS_ILOG_DFORK) ? 3 : 2].iov_len >
+	    XFS_DFORK_ASIZE(dip, mp)) {
+		error = -EFSCORRUPTED;
+		goto out_release;
+	}
+
 	switch (fields & XFS_ILOG_DFORK) {
 	case XFS_ILOG_DDATA:
 	case XFS_ILOG_DEXT:
@@ -546,7 +565,6 @@ xlog_recover_inode_commit_pass2(
 		case XFS_ILOG_ADATA:
 		case XFS_ILOG_AEXT:
 			dest = XFS_DFORK_APTR(dip);
-			ASSERT(len <= XFS_DFORK_ASIZE(dip, mp));
 			memcpy(dest, src, len);
 			break;
 
-- 
2.53.0