[PATCH 7.3.y 2/2] xfs: check for buffer overruns when examining local/remote xattr entries

[Sasha Levin <sashal@kernel.org>]

From: "Darrick J. Wong" <djwong@kernel.org>

[ Upstream commit 91c41f9524906a8ebd2ae68c98a07b4bd5255ddb ]

LOLLM noticed that the xattr scrub and repair code can walk off the end
of the buffer if the xattr entry record starts so close to the end of
the buffer that there's not even space for the entry structure itself.
Strengthen the bounds checking here.

Cc: stable@vger.kernel.org # v4.15
Fixes: 13791d3b833428 ("xfs: scrub extended attribute leaf space")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/xfs/scrub/attr.c        | 12 ++++++++++++
 fs/xfs/scrub/attr_repair.c | 16 +++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/scrub/attr.c b/fs/xfs/scrub/attr.c
index f7c00ea1af5d3..f909e2b25158a 100644
--- a/fs/xfs/scrub/attr.c
+++ b/fs/xfs/scrub/attr.c
@@ -306,6 +306,12 @@ xchk_xattr_local_entry(
 	char				*name_end;
 	unsigned int			namesize;
 
+	name_end = (char *)lentry + offsetof(typeof(*lentry), nameval[0]);
+	if (name_end > buf_end) {
+		xchk_da_set_corrupt(ds, level);
+		return 0;
+	}
+
 	namesize = xfs_attr_leaf_entsize_local(lentry->namelen,
 			be16_to_cpu(lentry->valuelen));
 	name_end = (char *)lentry + namesize;
@@ -335,6 +341,12 @@ xchk_xattr_remote_entry(
 	char				*name_end;
 	unsigned int			namesize;
 
+	name_end = (char *)rentry + offsetof(typeof(*rentry), name[0]);
+	if (name_end > buf_end) {
+		xchk_da_set_corrupt(ds, level);
+		return 0;
+	}
+
 	namesize = xfs_attr_leaf_entsize_remote(rentry->namelen);
 	name_end = (char *)rentry + namesize;
 	if (rentry->namelen == 0) {
diff --git a/fs/xfs/scrub/attr_repair.c b/fs/xfs/scrub/attr_repair.c
index c7695d4cc8e7c..ad688f9f7ce94 100644
--- a/fs/xfs/scrub/attr_repair.c
+++ b/fs/xfs/scrub/attr_repair.c
@@ -285,6 +285,7 @@ xrep_xattr_salvage_local_attr(
 	struct xfs_attr_leaf_name_local	*lentry)
 {
 	struct xchk_xattr_buf		*ab = rx->sc->buf;
+	char				*name_end;
 	unsigned char			*value;
 	unsigned int			valuelen;
 	unsigned int			namesize;
@@ -293,10 +294,14 @@ xrep_xattr_salvage_local_attr(
 	 * Decode the leaf local entry format.  If something seems wrong, we
 	 * junk the attribute.
 	 */
+	name_end = (char *)lentry + offsetof(typeof(*lentry), nameval[0]);
+	if (name_end > buf_end)
+		return 0;
 	value = &lentry->nameval[lentry->namelen];
 	valuelen = be16_to_cpu(lentry->valuelen);
 	namesize = xfs_attr_leaf_entsize_local(lentry->namelen, valuelen);
-	if ((char *)lentry + namesize > buf_end)
+	name_end = (char *)lentry + namesize;
+	if (name_end > buf_end)
 		return 0;
 	if (!xrep_xattr_want_salvage(rx, ent->flags, lentry->nameval,
 			lentry->namelen, value, valuelen))
@@ -333,8 +338,8 @@ xrep_xattr_salvage_remote_attr(
 		.attr_filter		= ent->flags & XFS_ATTR_NSP_ONDISK_MASK,
 		.namelen		= rentry->namelen,
 		.name			= rentry->name,
-		.valuelen		= be32_to_cpu(rentry->valuelen),
 	};
+	char				*name_end;
 	unsigned int			namesize;
 	int				error;
 
@@ -343,9 +348,14 @@ xrep_xattr_salvage_remote_attr(
 	 * junk the attribute.  Note that we should never find a zero-length
 	 * remote attribute value.
 	 */
+	name_end = (char *)rentry + offsetof(typeof(*rentry), name[0]);
+	if (name_end > buf_end)
+		return 0;
 	namesize = xfs_attr_leaf_entsize_remote(rentry->namelen);
-	if ((char *)rentry + namesize > buf_end)
+	name_end = (char *)rentry + namesize;
+	if (name_end > buf_end)
 		return 0;
+	args.valuelen = be32_to_cpu(rentry->valuelen);
 	if (args.valuelen == 0 ||
 	    !xrep_xattr_want_salvage(rx, ent->flags, rentry->name,
 			rentry->namelen, NULL, args.valuelen))
-- 
2.53.0