Comment 4 for bug 2007796

Hi, I upgraded my system to Kinetic in ~March, so I no longer have a setup
to test with. Kinetic's newer glibc with the change identified here works
for me.

On Tue, Jun 6, 2023, 4:02 PM Brian Murray <email address hidden>
wrote:

> Hello jandryuk, or anyone else affected,
>
> Accepted glibc into jammy-proposed. The package will build now and be
> available at https://launchpad.net/ubuntu/+source/glibc/2.35-0ubuntu3.2
> in a few hours, and then in the -proposed repository.
>
> Please help us by testing this new package. See
> https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
> to enable and use -proposed. Your feedback will aid us getting this
> update out to other Ubuntu users.
>
> If this package fixes the bug for you, please add a comment to this bug,
> mentioning the version of the package you tested, what testing has been
> performed on the package and change the tag from verification-needed-
> jammy to verification-done-jammy. If it does not fix the bug for you,
> please add a comment stating that, and change the tag to verification-
> failed-jammy. In either case, without details of your testing we will
> not be able to proceed.
>
> Further information regarding the verification process can be found at
> https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in
> advance for helping!
>
> N.B. The updated package will be released to -updates after the bug(s)
> fixed by this package have been verified and the package has been in
> -proposed for a minimum of 7 days.
>
> ** Changed in: glibc (Ubuntu Jammy)
> Status: In Progress => Fix Committed
>
> ** Tags added: verification-needed verification-needed-jammy
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/2007796
>
> Title:
> glibc __read_chk not a cancellation point
>
> Status in glibc package in Ubuntu:
> Fix Released
> Status in glibc source package in Jammy:
> Fix Committed
> Status in glibc source package in Kinetic:
> Fix Released
>
> Bug description:
> [Impact]
> I'm working with Xen and libxenstore. libxenstore, when using a
> "watch", spawns a pthread (read_thread). When libxenstore shuts down, it
> pthread_cancel()s and pthread_join()s the "watch" thread.
>
> That thread never exits and the process shutdown hangs.
>
> read_threads is sitting in __read_chk(). In glibc 2.35, __read_chk is
> not a cancellation point, so the thread never reacts to the
> cancellation.
>
> Upstream glibc fixed it in 2.36 in
>
> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=dc30acf20bd635d71cd4c84100e842fdf0429e48
>
> Here's the 2.35 disassembly - the lack of __pthread_enable_asynccancel()
> indicates the missing cancellation support:
> (gdb) disassemble
> Dump of assembler code for function __read_chk:
> 0x00007ffff7ea04d0 <+0>: endbr64
> 0x00007ffff7ea04d4 <+4>: cmp %rcx,%rdx
> 0x00007ffff7ea04d7 <+7>: ja 0x7ffff7ea0504 <__read_chk+52>
> 0x00007ffff7ea04d9 <+9>: xor %eax,%eax
> 0x00007ffff7ea04db <+11>: syscall
> => 0x00007ffff7ea04dd <+13>: cmp $0xfffffffffffff000,%rax
> 0x00007ffff7ea04e3 <+19>: ja 0x7ffff7ea04f0 <__read_chk+32>
> 0x00007ffff7ea04e5 <+21>: ret
> 0x00007ffff7ea04e6 <+22>: cs nopw 0x0(%rax,%rax,1)
> 0x00007ffff7ea04f0 <+32>: mov 0xe3919(%rip),%rdx #
> 0x7ffff7f83e10
> 0x00007ffff7ea04f7 <+39>: neg %eax
> 0x00007ffff7ea04f9 <+41>: mov %eax,%fs:(%rdx)
> 0x00007ffff7ea04fc <+44>: mov $0xffffffffffffffff,%rax
> 0x00007ffff7ea0503 <+51>: ret
> 0x00007ffff7ea0504 <+52>: push %rax
> 0x00007ffff7ea0505 <+53>: call 0x7ffff7ea00b0 <__GI___chk_fail>
> End of assembler dump.
>
> [Test procedure]
>
> The patch includes a test for this that is run at build time.
>
> [Regression potential]
>
> Besides the usual risks with any glibc update, this could potentially
> surface some race conditions at thread shutdown in user applications
> that were thus far hidden by the lack of cancellation point.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/2007796/+subscriptions
>
>