The patch titled
Subject: mm: enforce the mapping_map_writable() check after call_mmap()
has been added to the -mm mm-unstable branch. Its filename is
mm-enforce-the-mapping_map_writable-check-after-call_mmap.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-enforce-the-mapping_map_writable-check-after-call_mmap.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Subject: mm: enforce the mapping_map_writable() check after call_mmap()
Date: Sat, 7 Oct 2023 21:51:01 +0100
In order for an F_SEAL_WRITE sealed memfd mapping to have an opportunity
to clear VM_MAYWRITE in seal_check_write() we must be able to invoke
either the shmem_mmap() or hugetlbfs_file_mmap() f_ops->mmap() handler to
do so.
We would otherwise fail the mapping_map_writable() check before we had the
opportunity to clear VM_MAYWRITE.
However, the existing logic in mmap_region() performs this check BEFORE
calling call_mmap() (which invokes file->f_ops->mmap()). We must enforce
this check AFTER the function call.
In order to avoid any risk of breaking call_mmap() handlers which assume
this will have been done first, we continue to mark the file writable
first, simply deferring enforcement of it failing until afterwards.
This enables mmap(..., PROT_READ, MAP_SHARED, fd, 0) mappings for memfd's
sealed via F_SEAL_WRITE to succeed, whereas previously they were not
permitted.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238
Link: https://lkml.kernel.org/r/d2748bc4077b53c60bcb06fccaf976cb2afee345.1696709413.git.lstoakes@xxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
--- a/mm/mmap.c~mm-enforce-the-mapping_map_writable-check-after-call_mmap
+++ a/mm/mmap.c
@@ -2845,11 +2845,10 @@ cannot_expand:
vma->vm_pgoff = pgoff;
if (file) {
- if (is_shared_maywrite(vm_flags)) {
- error = mapping_map_writable(file->f_mapping);
- if (error)
- goto free_vma;
- }
+ int writable_error = 0;
+
+ if (vma_is_shared_maywrite(vma))
+ writable_error = mapping_map_writable(file->f_mapping);
vma->vm_file = get_file(file);
error = call_mmap(file, vma);
@@ -2857,6 +2856,15 @@ cannot_expand:
goto unmap_and_free_vma;
/*
+ * call_mmap() may have changed VMA flags, so retry this check
+ * if it failed before.
+ */
+ if (writable_error && vma_is_shared_maywrite(vma)) {
+ error = writable_error;
+ goto close_and_free_vma;
+ }
+
+ /*
* Expansion is handled above, merging is handled below.
* Drivers should not alter the address of the VMA.
*/
_
Patches currently in -mm which might be from lstoakes@xxxxxxxxx are
mm-filemap-clarify-filemap_fault-comments-for-not-uptodate-case.patch
mm-filemap-clarify-filemap_fault-comments-for-not-uptodate-case-fix.patch
mm-make-__access_remote_vm-static.patch
mm-gup-explicitly-define-and-check-internal-gup-flags-disallow-foll_touch.patch
mm-gup-make-failure-to-pin-an-error-if-foll_nowait-not-specified.patch
mm-gup-adapt-get_user_page_vma_remote-to-never-return-null.patch
mm-move-vma_policy-and-anon_vma_name-decls-to-mm_typesh.patch
mm-abstract-the-vma_merge-split_vma-pattern-for-mprotect-et-al.patch
mm-make-vma_merge-and-split_vma-internal.patch
mm-abstract-merge-for-new-vmas-into-vma_merge_new_vma.patch
mm-abstract-vma-merge-and-extend-into-vma_merge_extend-helper.patch
mm-drop-the-assumption-that-vm_shared-always-implies-writable.patch
mm-update-memfd-seal-write-check-to-include-f_seal_write.patch
mm-enforce-the-mapping_map_writable-check-after-call_mmap.patch
