mm: update memfd seal write check to include F_SEAL_WRITE

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>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 926d01c493fb330112bc23fb4d305398d81ee0a3..85cd418d234029abc4788032be1c8b255d301b53 100644 (file)
--- 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 c3b5749ede9d4e13d32b43838d0b18326328c5fb..86e040e886e4632c21020239ed28a0827bffcbfc 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4076,25 +4076,26 @@ 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 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

diff --git a/mm/shmem.c b/mm/shmem.c
index 61b170324e5ceccdb11ca3d5f4525e31899f28d5..bcbe9dbb9f5fc815687edbaa0c2c65499efc4568 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2378,7 +2378,7 @@ 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;