The quilt patch titled
Subject: mm: perform the mapping_map_writable() check after call_mmap()
has been removed from the -mm tree. Its filename was
mm-perform-the-mapping_map_writable-check-after-call_mmap.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Subject: mm: perform the mapping_map_writable() check after call_mmap()
Date: Thu, 12 Oct 2023 18:04:30 +0100
In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to
clear VM_MAYWRITE, we must be able to invoke the appropriate
vm_ops->mmap() handler to do so. We would otherwise fail the
mapping_map_writable() check before we had the opportunity to avoid it.
This patch moves this check after the call_mmap() invocation. Only memfd
actively denies write access causing a potential failure here (in
memfd_add_seals()), so there should be no impact on non-memfd cases.
This patch makes the userland-visible change that MAP_SHARED, PROT_READ
mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed.
There is a delicate situation with cleanup paths assuming that a writable
mapping must have occurred in circumstances where it may now not have. In
order to ensure we do not accidentally mark a writable file unwritable by
mistake, we explicitly track whether we have a writable mapping and unmap
only if we do.
[lstoakes@xxxxxxxxx: do not set writable_file_mapping in inappropriate case]
Link: https://lkml.kernel.org/r/c9eb4cc6-7db4-4c2b-838d-43a0b319a4f0@lucifer.local
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238
Link: https://lkml.kernel.org/r/55e413d20678a1bb4c7cce889062bbb07b0df892.1697116581.git.lstoakes@xxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
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 | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
--- a/mm/mmap.c~mm-perform-the-mapping_map_writable-check-after-call_mmap
+++ a/mm/mmap.c
@@ -2752,6 +2752,7 @@ unsigned long mmap_region(struct file *f
unsigned long charged = 0;
unsigned long end = addr + len;
unsigned long merge_start = addr, merge_end = end;
+ bool writable_file_mapping = false;
pgoff_t vm_pgoff;
int error;
VMA_ITERATOR(vmi, mm, addr);
@@ -2846,17 +2847,19 @@ 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;
- }
-
vma->vm_file = get_file(file);
error = call_mmap(file, vma);
if (error)
goto unmap_and_free_vma;
+ if (vma_is_shared_maywrite(vma)) {
+ error = mapping_map_writable(file->f_mapping);
+ if (error)
+ goto close_and_free_vma;
+
+ writable_file_mapping = true;
+ }
+
/*
* Expansion is handled above, merging is handled below.
* Drivers should not alter the address of the VMA.
@@ -2937,7 +2940,7 @@ cannot_expand:
/* Once vma denies write, undo our temporary denial count */
unmap_writable:
- if (file && is_shared_maywrite(vm_flags))
+ if (writable_file_mapping)
mapping_unmap_writable(file->f_mapping);
file = vma->vm_file;
ksm_add_vma(vma);
@@ -2985,7 +2988,7 @@ unmap_and_free_vma:
unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start,
vma->vm_end, vma->vm_end, true);
}
- if (file && is_shared_maywrite(vm_flags))
+ if (writable_file_mapping)
mapping_unmap_writable(file->f_mapping);
free_vma:
vm_area_free(vma);
_
Patches currently in -mm which might be from lstoakes@xxxxxxxxx are
