On Wed, Feb 12, 2020 at 07:51:18PM +0000, Al Viro wrote: > On Wed, Feb 12, 2020 at 08:15:08PM +0100, Florian Weimer wrote: > > > | Further, I've found some inconsistent behavior with ext4: chmod on the > > | magic symlink fails with EOPNOTSUPP as in Florian's test, but fchmod > > | on the O_PATH fd succeeds and changes the symlink mode. This is with > > | 5.4. Cany anyone else confirm this? Is it a problem? > > > > It looks broken to me because fchmod (as an inode-changing operation) > > is not supposed to work on O_PATH descriptors. > > Why? O_PATH does have an associated inode just fine; where does > that "not supposed to" come from? Indeed, my expectation was that both fchmod and chmod via the magic symlink succeed, given a new enough kernel for operations on O_PATH fds to be supported. I'd like to switch to using fstat+fchmod to do this, and only fallback to /proc on older kernels where O_PATH fds cause EBADF. But I'm somewhat concerned by the inconsistency between behavior of the two approaches. Rich
