Messages in this thread | | | Date | Sun, 29 Mar 2009 23:20:22 +0100 | From | Al Viro <> | Subject | Re: Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid sometimes doesn't) |
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On Sun, Mar 29, 2009 at 11:36:35PM +0200, Oleg Nesterov wrote: > > ... or just do that to fs_struct. After finding that there's no outside > > users. Commenst? > > This is even worse. Not only we race with our sub-threads, we race > with CLONE_FS processes. > > We can't mark fs_struct after finding that there's no outside users > lockless. Because we can't know whether this is "after" or not, we > can't trust "atomic_read(fs->count) <= n_fs".
We can lock fs_struct in question, go through the threads, then mark or bail out. With cloning a reference to fs_struct protected by the same lock.
FWIW, I'm not at all sure that we want atomic_t for refcount in that case...
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