On Mon 03-04-23 23:28:32, Lorenzo Stoakes wrote:
> 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;
Shouldn't we rather jump to close_and_free_vma?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
