чт, 16 янв. 2020 г. в 01:05, ronnie sahlberg <ronniesahlberg@xxxxxxxxx>:
>
> The bug is basically that if we extend a file by fallocate mode==0
> and immediately afterwards mmap() the file we will only mmap() as much
> as end-of-file was
> prior to the truncate and then if we try to touch any
> address in this extended region userspace dies with bus error.
>
> The patch added "extend a file with fallocate mode==0 for NON-Sparse
> files" and caused xfstest to fail.
> The fix is to force us to revalidate the file attributes (the size is
> the important one) when we extend the file so
> mmap() will work properly.
> I have fixed this in the patch and will resend tomorrow after some more testing.
>
> Looking for other SMB2_set_eof() callsites I see we already had the
> same bug for the case of extending a SPARSE
I agree that regardless of file being sparse or not, we should somehow
update a size in the VFS after calling SMB2_set_eof().
> file using fallocate mode==0. I fixed that too and will audit all
> other plases where we use SMB2_set_eof()
> to see if they are safe or not before resending.
One of those places where SMB2_set_eof() is called is
cifs_set_file_size() which does call the following after getting a
successful response from the server:
2250 >-------if (rc == 0) {
2251 >------->-------cifsInode->server_eof = attrs->ia_size;
2252 >------->-------cifs_setsize(inode, attrs->ia_size);
2253 >------->-------cifs_truncate_page(inode->i_mapping, inode->i_size);
2254 >-------}
This is called by cifs_setattr_[no]unix() which does the following afterwards:
2569 >-------if ((attrs->ia_valid & ATTR_SIZE) &&
2570 >------- attrs->ia_size != i_size_read(inode))
2571 >------->-------truncate_setsize(inode, attrs->ia_size);
truncate_setsize() does similar things as cifs_setsize() besides
setting cinode->time to 0. This code path probably needs to be
refactored. But putting this aside, for the current fallocate fix I
think we should use the same existing mechanism to update a file size
in the VFS without revalidating the inode.
--
Best regards,
Pavel Shilovsky
