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. > > > > Does POSIX actually make any promises in that area? That would affect > > how high a cost we ought to pay for that - I agree that it would be nicer > > to have atomicity from userland point of view, but there's a difference > > between hard bug and QoI issue. > > As I understand the original report, it relies on us hitting the nlink == > 0 at exactly the wrong moment. Can't we just restart the entire path > resolution if we find a target with nlink == 0? Sure, it's a lot of > extra work, but you've got to be trying hard to hit it in the first place. touch /tmp/blah exec 42</tmp/blah rm /tmp/blah ... call linkat() with AT_SYMLINK_FOLLOW and /proc/self/fd/42 for source Your variant will loop indefinitely on that...
