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.
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
---
mm/mmap.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index c96dcce90772..a166e9f3c474 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2596,17 +2596,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
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 unmap_and_free_vma;
+ }
+
/*
* Expansion is handled above, merging is handled below.
* Drivers should not alter the address of the VMA.
--
2.40.0
