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Date: Fri, 27 Mar 2020 14:16:54 -0400
From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Cc: Leonid Shamis <leonid.shamis@gmail.com>
Message-ID: <20200327181654.GH11469@brightrain.aerifal.cx>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] __pthread_mutex_unlock uninitialized value

On Fri, Mar 27, 2020 at 10:52:58AM -0700, Leonid Shamis wrote:
> https://github.com/bminor/musl/blob/54ca677983d47529bab8752315ac1a2b49888870/src/thread/pthread_mutex_unlock.c#L34

BTW official git is here:

https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_mutex_unlock.c?id=v1.2.0

> In the case where a mutex:
> is one of PTHREAD_MUTEX_ERRORCHECK or PTHREAD_MUTEX_RECURSIVE
> and PTHREAD_PRIO_INHERIT
> 
> an uninitialized value of 'old' is used to check whether to futex.

Can you elaborate on this? In line 15, old is assigned; this applies
to all mutex types except plain boring normal (without PI and without
robust). The condition in line 33 can only be true if type is nonzero
(not plain boring normal mutex) so I don't see any way it can be used
uninitialized in line 34. Is your report based on your own reading or
a static analysis tool?

Rich