[PATCH 08/28] xfs: validate attr entry pointer before field access

[Andrey Albershteyn <aalbersh@kernel.org>]

From: Hongling Zeng <zenghongling@kylinos.cn>

Source kernel commit: b7eea80be25f3334f131d52982b3131aba77b97d

xfs_attr3_leaf_verify_entry() accesses lentry/rentry fields (namelen,
valuelen) before checking if the entry pointer itself is within bounds.
If nameidx is crafted to point near the end of the buffer, these field
accesses can read out-of-bounds before the bounds check at
name_end > buf_end is performed.

Add explicit bounds checks for entry pointers before accessing their
fields. Use offsetof() to check that the start of the flexible array
member (nameval/name) is within bounds, which ensures all preceding
fields are safe to access.

Fixes: c84760659dcf2 ("xfs: check attribute leaf block structure")
Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
---
 libxfs/xfs_attr_leaf.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libxfs/xfs_attr_leaf.c b/libxfs/xfs_attr_leaf.c
index 86c5c09a5db4..b6288395f853 100644
--- a/libxfs/xfs_attr_leaf.c
+++ b/libxfs/xfs_attr_leaf.c
@@ -325,6 +325,13 @@ xfs_attr3_leaf_verify_entry(
 	 */
 	if (ent->flags & XFS_ATTR_LOCAL) {
 		lentry = xfs_attr3_leaf_name_local(leaf, idx);
+
+		/* Validate lentry pointer is within bounds before field access */
+		if ((char *)lentry >= buf_end)
+			return __this_address;
+		if ((char *)lentry + offsetof(struct xfs_attr_leaf_name_local, nameval) > buf_end)
+			return __this_address;
+
 		namesize = xfs_attr_leaf_entsize_local(lentry->namelen,
 				be16_to_cpu(lentry->valuelen));
 		name_end = (char *)lentry + namesize;
@@ -332,6 +339,13 @@ xfs_attr3_leaf_verify_entry(
 			return __this_address;
 	} else {
 		rentry = xfs_attr3_leaf_name_remote(leaf, idx);
+
+		/* Validate rentry pointer is within bounds before field access */
+		if ((char *)rentry >= buf_end)
+			return __this_address;
+		if ((char *)rentry + offsetof(struct xfs_attr_leaf_name_remote, name) > buf_end)
+			return __this_address;
+
 		namesize = xfs_attr_leaf_entsize_remote(rentry->namelen);
 		name_end = (char *)rentry + namesize;
 		if (rentry->namelen == 0)
-- 
2.54.0