Messages in this thread | | | Date | Tue, 21 Mar 2006 11:16:05 -0800 | From | Chris Wright <> | Subject | Re: DoS with POSIX file locks? |
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* Miklos Szeredi (miklos@szeredi.hu) wrote: > > > Apps using LinuxThreads seem to be candidates: > > > > > > According to POSIX 1003.1c, a successful `exec*' in one of the > > > threads should automatically terminate all other threads in the > > > program. This behavior is not yet implemented in LinuxThreads. > > > Calling `pthread_kill_other_threads_np' before `exec*' achieves > > > much of the same behavior, except that if `exec*' ultimately > > > fails, then all other threads are already killed. > > > > > > steal_locks() was probably added as a workaround for this case, no? > > > > Possibly, but LinuxThreads were never really POSIX thread compliant > > anyway. Anyhow, the problem isn't really LinuxThreads, it is rather that > > the existence of the standalone CLONE_FILES flag allows you to do a lot > > of weird inheritance crap with 'posix locks' that the POSIX standards > > committees never even had to consider. > > Yes. The execve-with-multiple-threads/posix-locks interaction is not > documented for LinuxThreads but removing steal_locks() makes that > implementation slighly differently incompatible to POSIX. Some > application _might_ be relying on the current behavior. > > It's just a question of how much confidence do we have, that no app > will break if steal_locks() is removed. This function was added by > Chris Wright on 2003-12-29 (Cset 1.1371.111.3): > > Add steal_locks helper for use in conjunction with unshare_files to > make sure POSIX file lock semantics aren't broken due to > unshare_files. > > Chris, do you remember if this was due to some concrete breakage or > just a preemtive measure?
Concrete breakage. Something like:
clone(CLONE_FILES) /* in child */ lock execve lock
w/out the kludge[1], the lock fails. I should have a test program about that I wrote to test this, although it was originally triggered via some LTP or LSB type of test (don't recall which).
thanks, -chris
[1] happy to see it go. i concur with Trond, there's no sane way to get rid of it w/out formalizing CLONE_FILES and locks on exec - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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