[PATCH 05/16] hugetlbfs: enforce F_SEAL_EXEC in setattr

[David Hildenbrand (Arm)]

From: Eva Kurchatova <eva.kurchatova@xxxxxxxxxxxxx>

F_SEAL_EXEC is enforced by shmem_setattr(), but hugetlbfs_setattr() does
not check it. As a result, fchmod() can change the execute bits of a
sealed hugetlbfs memfd.

Use memfd_check_seals_mode() in hugetlbfs_setattr() to reject changes
to execute bits when F_SEAL_EXEC is set.

This also fixes the memfd_test hugetlbfs SEAL-EXEC subtest, where
fchmod() incorrectly succeeded after applying F_SEAL_EXEC.

LLM assistance was used to reuse the helper and revise the description.

Fixes: 6fd7353829ca ("mm/memfd: add F_SEAL_EXEC")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Eva Kurchatova <eva.kurchatova@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260629180247.2343229-1-eva.kurchatova@xxxxxxxxxxxxx
[ david: use common helper; fixup Fixes: ]
Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 fs/hugetlbfs/inode.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 6656807ce4377..7f5c3962b5d56 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -28,6 +28,7 @@
 #include <linux/folio_batch.h>
 #include <linux/fs_parser.h>
 #include <linux/mman.h>
+#include <linux/memfd.h>
 #include <linux/slab.h>
 #include <linux/dnotify.h>
 #include <linux/statfs.h>
@@ -841,6 +842,13 @@ static int hugetlbfs_setattr(const struct mnt_idmap *idmap,
 	if (error)
 		return error;
 
+	if (ia_valid & ATTR_MODE) {
+		error = memfd_check_seals_mode(info->seals, inode->i_mode,
+					       attr->ia_mode);
+		if (error)
+			return error;
+	}
+
 	trace_hugetlbfs_setattr(inode, dentry, attr);
 
 	if (ia_valid & ATTR_SIZE) {

-- 
2.43.0