Patch "mm: update memfd seal write check to include F_SEAL_WRITE" has been added to the 5.10-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: update memfd seal write check to include F_SEAL_WRITE

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-update-memfd-seal-write-check-to-include-f_seal_write.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From 3SXuJaA4KBrAYiQQScQdZQhhUiWeeWbU.SecWhUWaXbYdknVekdTQjYed.ehW@flex--isaacmanjarres.bounces.google.com Wed Jul 30 03:54:18 2025
From: "Isaac J. Manjarres" <isaacmanjarres@google.com>
Date: Tue, 29 Jul 2025 18:54:00 -0700
Subject: mm: update memfd seal write check to include F_SEAL_WRITE
To: lorenzo.stoakes@oracle.com, gregkh@linuxfoundation.org,  Muchun Song <muchun.song@linux.dev>, Oscar Salvador <osalvador@suse.de>,  David Hildenbrand <david@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,  "Liam R. Howlett" <Liam.Howlett@oracle.com>, Vlastimil Babka <vbabka@suse.cz>,  Mike Rapoport <rppt@kernel.org>, Suren Baghdasaryan <surenb@google.com>, Michal Hocko <mhocko@suse.com>,  Hugh Dickins <hughd@google.com>, Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: aliceryhl@google.com, stable@vger.kernel.org,  "Isaac J. Manjarres" <isaacmanjarres@google.com>, kernel-team@android.com,  Lorenzo Stoakes <lstoakes@gmail.com>, Jan Kara <jack@suse.cz>,  Alexander Viro <viro@zeniv.linux.org.uk>, Andy Lutomirski <luto@kernel.org>,  Christian Brauner <brauner@kernel.org>, "Matthew Wilcox (Oracle)" <willy@infradead.org>,  Mike Kravetz <mike.kravetz@oracle.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Message-ID: <20250730015406.32569-3-isaacmanjarres@google.com>

From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 28464bbb2ddc199433383994bcb9600c8034afa1 ]

The seal_check_future_write() function is called by shmem_mmap() or
hugetlbfs_file_mmap() to disallow any future writable mappings of an memfd
sealed this way.

The F_SEAL_WRITE flag is not checked here, as that is handled via the
mapping->i_mmap_writable mechanism and so any attempt at a mapping would
fail before this could be run.

However we intend to change this, meaning this check can be performed for
F_SEAL_WRITE mappings also.

The logic here is equally applicable to both flags, so update this
function to accommodate both and rename it accordingly.

Link: https://lkml.kernel.org/r/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/hugetlbfs/inode.c |    2 +-
 include/linux/mm.h   |   15 ++++++++-------
 mm/shmem.c           |    2 +-
 3 files changed, 10 insertions(+), 9 deletions(-)

--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -148,7 +148,7 @@ static int hugetlbfs_file_mmap(struct fi
 	vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND;
 	vma->vm_ops = &hugetlb_vm_ops;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3201,25 +3201,26 @@ unsigned long wp_shared_mapping_range(st
 extern int sysctl_nr_trim_pages;
 
 /**
- * seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it
+ * seal_check_write - Check for F_SEAL_WRITE or F_SEAL_FUTURE_WRITE flags and
+ *                    handle them.
  * @seals: the seals to check
  * @vma: the vma to operate on
  *
- * Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on
- * the vma flags.  Return 0 if check pass, or <0 for errors.
+ * Check whether F_SEAL_WRITE or F_SEAL_FUTURE_WRITE are set; if so, do proper
+ * check/handling on the vma flags.  Return 0 if check pass, or <0 for errors.
  */
-static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
+static inline int seal_check_write(int seals, struct vm_area_struct *vma)
 {
-	if (seals & F_SEAL_FUTURE_WRITE) {
+	if (seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
 		/*
 		 * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
-		 * "future write" seal active.
+		 * write seals are active.
 		 */
 		if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
 			return -EPERM;
 
 		/*
-		 * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as
+		 * Since an F_SEAL_[FUTURE_]WRITE sealed memfd can be mapped as
 		 * MAP_SHARED and read-only, take care to not allow mprotect to
 		 * revert protections on such mappings. Do this only for shared
 		 * mappings. For private mappings, don't need to mask
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2263,7 +2263,7 @@ static int shmem_mmap(struct file *file,
 	struct shmem_inode_info *info = SHMEM_I(file_inode(file));
 	int ret;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 


Patches currently in stable-queue which might be from isaacmanjarres@google.com are

queue-5.10/mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
queue-5.10/selftests-memfd-add-test-for-mapping-write-sealed-memfd-read-only.patch
queue-5.10/mm-reinstate-ability-to-map-write-sealed-memfd-mappings-read-only.patch
queue-5.10/mm-update-memfd-seal-write-check-to-include-f_seal_write.patch