Re: [Q] eCryptFS race window?

From: Cyrill Gorcunov
Date: Tue May 20 2008 - 14:54:40 EST

[Michael Halcrow - Tue, May 20, 2008 at 01:27:57PM -0500]
| On Tue, May 20, 2008 at 09:03:21PM +0400, Cyrill Gorcunov wrote:
| > it seems there is a few potential race window in eCryptFS which I
| > was trying to fix but it requires more deeper eCrypFS knowledge that
| > have (at least only by understanding eCryptFS in big picture it is
| > possible to fix this problem by elegant path). So what is the
| > problem - the procedures
| >
| > ecryptfs_miscdev_poll
| > ecryptfs_miscdev_read
| >
| > does take ecryptfs_daemon_hash_mux mutex and then daemon->mux _but_
| > releases them not in exactly backward order as it should. My patches
| > (not in mainline but you saw them) was screwed up 'cause
| > mutex_is_locked could release mutex acquired by another process and
| > that is wrong. But I've a hope that I'm simply *wrong* about this
| > possible races ;) Take a look please.
| I cannot find an execution path whereby one of the two must re-acquire
| ecryptfs_daemon_hash_mux in order to release daemon->mux, so I do not
| think we will ever have deadlock between those two functions.
| Mike

Anyway, don't apply my patch you've tested (which I've replied to
Ingo's circular dep report), please, it's screwed ;) The patch Andrew
has taken to its tree is ok.

- Cyrill -
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