[PATCH] erofs-utils: lib: validate h_shared_count in erofs_init_inode_xattrs()

[Utkal Singh <singhutkal015@gmail.com>]

erofs_init_inode_xattrs() reads h_shared_count directly from the on-disk
xattr ibody header and uses it to size a heap allocation and drive a
read loop without checking whether the implied shared xattr array fits
within xattr_isize.

A crafted EROFS image with a large h_shared_count but a minimal
xattr_isize causes the subsequent loop to read shared xattr entries
beyond the xattr ibody boundary, interpreting unrelated on-disk data
as shared xattr IDs.  This affects every library consumer -- dump.erofs,
erofsfuse, and the rebuild path (lib/rebuild.c) -- none of which call
the fsck-only erofs_verify_xattr() before reaching this code.

Validate that h_shared_count fits within the available xattr body space
before allocating or reading.  Use a division-based check to avoid any
theoretical overflow in the multiplication.

The subtraction is safe because callers above already reject
xattr_isize < sizeof(struct erofs_xattr_ibody_header).

Signed-off-by: Utkal Singh <singhutkal015@gmail.com>
---
 lib/xattr.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/xattr.c b/lib/xattr.c
index 565070a..6891812 100644
--- a/lib/xattr.c
+++ b/lib/xattr.c
@@ -1182,6 +1182,16 @@ static int erofs_init_inode_xattrs(struct erofs_inode *vi)
 
 	ih = it.kaddr;
 	vi->xattr_shared_count = ih->h_shared_count;
+	/* validate h_shared_count fits within xattr_isize */
+	if (vi->xattr_shared_count >
+	    (vi->xattr_isize - sizeof(struct erofs_xattr_ibody_header)) /
+			sizeof(u32)) {
+		erofs_err("bogus h_shared_count %u (xattr_isize %u) @ nid %llu",
+			  vi->xattr_shared_count, vi->xattr_isize,
+			  vi->nid | 0ULL);
+		erofs_put_metabuf(&it.buf);
+		return -EFSCORRUPTED;
+	}
 	vi->xattr_shared_xattrs = malloc(vi->xattr_shared_count * sizeof(uint));
 	if (!vi->xattr_shared_xattrs) {
 		erofs_put_metabuf(&it.buf);
-- 
2.43.0