linux-kernel - [RFC PATCH 2/3] mm: update seal_check_[future_]write() to include F_SEAL

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Date:   Mon,  3 Apr 2023 23:28:31 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Lorenzo Stoakes <lstoakes@...il.com>
Subject: [RFC PATCH 2/3] mm: update seal_check_[future_]write() to include F_SEAL_WRITE as well

Check for F_SEAL_WRITE as well for which the precise same logic can
reasonably be applied, however so far this code will simply not be run as
the mapping_map_writable() call occurs before shmem_mmap() or
hugetlbfs_file_mmap() and thus would error out in the case of a read-only
shared mapping before the logic could be applied.

This therefore has no impact until the following patch which changes the
order in which the *_mmap() functions are called.

Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
 fs/hugetlbfs/inode.c |  2 +-
 include/linux/mm.h   | 13 +++++++------
 mm/shmem.c           |  2 +-
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 702d79639c0d..8ab8840707ac 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -135,7 +135,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 	vm_flags_set(vma, 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;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8e64041b1703..ddf1b35b9dbb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3775,16 +3775,17 @@ static inline void mem_dump_obj(void *object) {}
 #endif
 
 /**
- * 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 flag and
+ *                    handle it.
  * @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.
@@ -3793,7 +3794,7 @@ static inline int seal_check_future_write(int seals, struct vm_area_struct *vma)
 			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
diff --git a/mm/shmem.c b/mm/shmem.c
index 9218c955f482..863f2ff9fab8 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2313,7 +2313,7 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	int ret;
 
-	ret = seal_check_future_write(info->seals, vma);
+	ret = seal_check_write(info->seals, vma);
 	if (ret)
 		return ret;
 
-- 
2.40.0