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Message-ID: <20250730005818.2793577-4-isaacmanjarres@google.com>
Date: Tue, 29 Jul 2025 17:58:08 -0700
From: "Isaac J. Manjarres" <isaacmanjarres@...gle.com>
To: lorenzo.stoakes@...cle.com, gregkh@...uxfoundation.org,
Muchun Song <muchun.song@...ux.dev>, Oscar Salvador <osalvador@...e.de>,
David Hildenbrand <david@...hat.com>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Kees Cook <kees@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, Jann Horn <jannh@...gle.com>,
Pedro Falcato <pfalcato@...e.de>, Hugh Dickins <hughd@...gle.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: aliceryhl@...gle.com, stable@...r.kernel.org,
"Isaac J. Manjarres" <isaacmanjarres@...gle.com>, kernel-team@...roid.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Lorenzo Stoakes <lstoakes@...il.com>, Andy Lutomirski <luto@...nel.org>,
Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 5.4.y 3/3] mm: perform the mapping_map_writable() check after call_mmap()
From: Lorenzo Stoakes <lstoakes@...il.com>
[ Upstream commit 158978945f3173b8c1a88f8c5684a629736a57ac ]
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@...il.com: 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@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Muchun Song <muchun.song@...ux.dev>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: stable@...r.kernel.org
[isaacmanjarres: added error handling to cleanup the work done by the
mmap() callback and removed unused label.]
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
---
mm/mmap.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index cb712ae731cd..e591a82a26a8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1718,6 +1718,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev;
+ bool writable_file_mapping = false;
int error;
struct rb_node **rb_link, *rb_parent;
unsigned long charged = 0;
@@ -1785,11 +1786,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (error)
goto free_vma;
}
- if (is_shared_maywrite(vm_flags)) {
- error = mapping_map_writable(file->f_mapping);
- if (error)
- goto allow_write_and_free_vma;
- }
/* ->mmap() can change vma->vm_file, but must guarantee that
* vma_link() below can deny write-access if VM_DENYWRITE is set
@@ -1801,6 +1797,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
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;
+ }
+
/* Can addr have changed??
*
* Answer: Yes, several device drivers can do it in their
@@ -1823,7 +1827,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vma_link(mm, vma, prev, rb_link, rb_parent);
/* Once vma denies write, undo our temporary denial count */
if (file) {
- if (is_shared_maywrite(vm_flags))
+ if (writable_file_mapping)
mapping_unmap_writable(file->f_mapping);
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
@@ -1858,15 +1862,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
return addr;
+close_and_free_vma:
+ if (vma->vm_ops && vma->vm_ops->close)
+ vma->vm_ops->close(vma);
unmap_and_free_vma:
vma->vm_file = NULL;
fput(file);
/* Undo any partial mapping done by a device driver. */
unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
- if (is_shared_maywrite(vm_flags))
+ if (writable_file_mapping)
mapping_unmap_writable(file->f_mapping);
-allow_write_and_free_vma:
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
free_vma:
--
2.50.1.552.g942d659e1b-goog
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