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SubjectRe: race between vfs_rename and do_linkat (mv and link)
On Tue, 15 Feb 2022 at 17:20, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Tue, Feb 15, 2022 at 04:17:11PM +0000, Matthew Wilcox wrote:
> > On Tue, Feb 15, 2022 at 04:06:06PM +0000, Al Viro wrote:
> > > On Tue, Feb 15, 2022 at 01:37:40PM +0000, Al Viro wrote:
> > > > On Tue, Feb 15, 2022 at 10:56:29AM +0100, Miklos Szeredi wrote:
> > > >
> > > > > Doing "lock_rename() + lookup last components" would fix this race.
> > >
> > > "Fucking ugly" is inadequate for the likely results of that approach.
> > > It's guaranteed to be a source of headache for pretty much ever after.

So this is a fairly special situation. How about adding a new rwsem
(could possibly be global or per-fs)?

- acquired for read in lock_rename() before inode locks
- acquired for write in do_linkat before inode locks, but only on retry

Thanks,
Miklos

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