Re: [RFC PATCH] fs: introduce mkdirat2 syscall for atomic mkdir

On Sat, Feb 27, 2021 at 09:26:21PM -0500, Drew DeVault wrote:

On Sat Feb 27, 2021 at 9:24 PM EST, Matthew Wilcox wrote:

quoted

Where's the problem? If mkdir succeeds in a sticky directory, others
can't remove or rename it. So how can an app be tricked into doing
something wrong?

It's not a security concern, it's just about about making the software
more robust.

1. Program A creates a directory
2. Program A is pre-empted
3. Program B deletes the directory
4. Program A creates a file in that directory
5. RIP

umm ... program B deletes the directory.  program A opens it in order to
use openat().  program A gets ENOENT and exits, confused.  that's the
race you're removing here -- and it seems fairly insignificant to me.