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From: Rich Felker <>
To: "Appelmans, Madeleine" <>
Cc: "" <>
Subject: Re: [musl] Difference in pthread behavior between glibc and musl
Date: Tue, 11 Jul 2023 22:48:04 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Jul 11, 2023 at 07:19:50PM +0000, Appelmans, Madeleine wrote:
> Hello,
> There seems to be a difference in pthread behavior when compiling
> with glibc and using the musl-gcc wrapper. The attached snippet of
> code creates a destructor attribute which deletes a pthread key. The
> code never actually creates the pthread key. This code segfaults
> when compiled using musl-gcc, and does not segfault when compiled
> with gcc.
> Best guess at what is going on: When creating a pthread key, musl
> initializes a field called
> tsd<>.
> When deleting a key, musl assumes that initialization has been done,
> and dereferences tsd without checking that it exists: see
> here<>.
> This dereference may be the source of the segfault.

This is completely expected; the behavior is undefined because you
passed to pthread_key_delete a value which was not acquired via

If it happens not to crash on glibc, that doesn't mean it's okay to do
it. It will end up deleting whatever key happens to correspond to the
zero-initialized pthread_key_t object, which may be a key that was
allocated for use by some other part of the program when it called
pthread_key_create. (In other words, you have a type of double-free or
use-after-free bug.) Your program logic must ensure you refrain from
doing that.


  parent reply	other threads:[~2023-07-12  2:48 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-11 19:19 Appelmans, Madeleine
2023-07-11 19:42 ` Markus Wichmann
2023-07-12  2:48 ` Rich Felker [this message]
2023-07-13  1:00   ` Gabriel Ravier
2023-07-13  1:50     ` Rich Felker
2023-07-13  2:02       ` Gabriel Ravier
2023-07-13 16:27         ` Markus Wichmann
2023-07-13 18:49           ` Gabriel Ravier

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