[PATCH 6.6.y] hugetlbfs: enforce F_SEAL_EXEC in setattr

[Sasha Levin <sashal@kernel.org>]

From: Eva Kurchatova <eva.kurchatova@virtuozzo.com>

[ Upstream commit b7f570e7cea761ec7eb4a3a9557a3a082d14e88c ]

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.

Fixes: 6fd7353829ca ("mm/memfd: add F_SEAL_EXEC")
Cc: stable@vger.kernel.org
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
Link: https://patch.msgid.link/20260629180247.2343229-1-eva.kurchatova@virtuozzo.com
Acked-by: Pedro Falcato <pfalcato@suse.de>
Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Tested-by: Gregory Price (Meta) <gourry@gourry.net>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
[ david: use common helper; fixup Fixes:; check only regular files ]
Acked-by: Oscar Salvador <osalvador@suse.de>
Link: https://patch.msgid.link/20261029-fixes_shmem-v4-5-392fc715d8f6@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
[ sashal: replaced memfd_check_seals_mode() with an inline F_SEAL_EXEC and execute-bit check ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/hugetlbfs/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9bc9f04e4b7a6..96ba81081ed42 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -964,6 +964,12 @@ static int hugetlbfs_setattr(struct mnt_idmap *idmap,
 	if (error)
 		return error;
 
+	if (S_ISREG(inode->i_mode) && (ia_valid & ATTR_MODE)) {
+		if ((info->seals & F_SEAL_EXEC) &&
+		    ((inode->i_mode ^ attr->ia_mode) & 0111))
+			return -EPERM;
+	}
+
 	if (ia_valid & ATTR_SIZE) {
 		loff_t oldsize = inode->i_size;
 		loff_t newsize = attr->ia_size;
-- 
2.53.0