Dominique Martinet wrote on Sun, Dec 06, 2020:
> Chengguang Xu wrote on Sat, Dec 05, 2020:
> > If vma is shared and the file was opened for writing,
> > we should also create writeback fid because vma may be
> > mprotected writable even if now readonly.
>
> Hm, I guess it makes sense.
I had a second look, and generic_file_readonly_mmap uses vma's
`vma->vm_flags & VM_MAYWRITE` instead (together with VM_SHARED),
while mapping_writably_mapped ultimately basically only seems to
validate that the mapping is shared from a look at mapping_map_writable
callers? It's not very clear to me.
OTOH, VM_MAYWRITE is set anytime we have a shared map where file has
been opened read-write, which seems to be what you want with regards to
protecting from mprotect calls.
How about simply changing check from WRITE to MAYWRITE?
v9inode = V9FS_I(inode);
mutex_lock(&v9inode->v_mutex);
if (!v9inode->writeback_fid &&
(vma->vm_flags & VM_SHARED) &&
- (vma->vm_flags & VM_WRITE)) {
+ (vma->vm_flags & VM_MAYWRITE)) {
/*
* clone a fid and add it to writeback_fid
* we do it during mmap instead of
--
Dominique
