Bug 1267912

Summary:	malloc() signal leak in lexsave() [RHEL-7]
Product:	Red Hat Enterprise Linux 7	Reporter:	Kamil Dudka <kdudka>
Component:	zsh	Assignee:	Kamil Dudka <kdudka>
Status:	CLOSED ERRATA	QA Contact:	Jan Kepler <jkejda>
Severity:	high	Docs Contact:	Robert Krátký <rkratky>
Priority:	urgent
Version:	7.2	CC:	fkrska, isenfeld, jkejda, kdudka, ovasik, rkratky
Target Milestone:	rc	Keywords:	EasyFix, Patch, ZStream
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	zsh-5.0.2-17.el7	Doc Type:	Bug Fix
Doc Text:	zsh no longer deadlocks on `malloc()` execution Previously, if the zsh process received a signal during the execution of a memory allocation function and the signal handler attempted to allocate or free memory, zsh entered a deadlock and became unresponsive. With this update, signal handlers are no longer enabled while handling the global state of zsh or while using the heap memory allocator. This ensures that the described deadlock no longer occurs.	Story Points:	---
Clone Of:	1267903
Clones:	1338885 (view as bug list)		Environment:
Last Closed:	2016-11-03 23:02:21 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1203710, 1267903, 1289025, 1295396, 1295829, 1313485, 1338885

Description Kamil Dudka 2015-10-01 11:38:48 UTC

+++ This bug was initially created as a clone of Bug #1267903 +++

Description of problem:

zsh deadlocks in futex-wait state when signal hit in malloc() called by lexsave():


#0  __lll_lock_wait_private () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
97	2:	movl	%edx, %eax
(gdb) bt
#0  __lll_lock_wait_private () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
#1  0x0000003eb427d0a0 in _L_lock_5189 () from /lib64/libc-2.12.so
#2  0x0000003eb42789fb in _int_free (av=0x3eb458fe80, p=0x2174940, have_lock=0) at malloc.c:4959
...
#7  0x0000000000474495 in zhandler (sig=17) at signals.c:584
#8  <signal handler called>
#9  _int_malloc (av=0x3eb458fe80, bytes=<value optimized out>) at malloc.c:4538
#10 0x0000003eb427a991 in __libc_malloc (bytes=264) at malloc.c:3664
#11 0x000000000044a96b in lexsave () at lex.c:252

Version-Release number of selected component (if applicable):

zsh-4.3.11-4.el6.x86_64

How reproducible:

happens in production environment, not reproduced in labs so far

Steps to Reproduce:
1.
2.
3.

Actual results:

zsh deadlocks in futex-wait state

Expected results:

no deadlocks

Additional info:

The bug appears not to affect upstream master, where the function

lexsave(void)
 ... 1x malloc, 1x zalloc

was rewritten to

lex_context_save(struct lex_stack *ls, int toplevel)
  ... no *alloc at all

Recheck of any possible malloc() signal leaks in current RHEL 6 zsh code needed.

--- Additional comment from Kamil Dudka on 2015-10-01 13:30:30 CEST ---

(In reply to Filip Krska from comment #0)
> Description of problem:
> 
> zsh deadlocks in futex-wait state when signal hit in malloc() called by
> lexsave():
> 
> 
> #0  __lll_lock_wait_private () at
> ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
> 97	2:	movl	%edx, %eax
> (gdb) bt
> #0  __lll_lock_wait_private () at
> ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
> #1  0x0000003eb427d0a0 in _L_lock_5189 () from /lib64/libc-2.12.so
> #2  0x0000003eb42789fb in _int_free (av=0x3eb458fe80, p=0x2174940,
> have_lock=0) at malloc.c:4959
> ...
> #7  0x0000000000474495 in zhandler (sig=17) at signals.c:584
> #8  <signal handler called>
> #9  _int_malloc (av=0x3eb458fe80, bytes=<value optimized out>) at
> malloc.c:4538
> #10 0x0000003eb427a991 in __libc_malloc (bytes=264) at malloc.c:3664
> #11 0x000000000044a96b in lexsave () at lex.c:252

I agree that replacing malloc() by zalloc() will prevent the above backtrace.

> Recheck of any possible malloc() signal leaks in current RHEL 6 zsh code
> needed.

It is unfortunately not that easy.  Calling [z]free() can also cause such a deadlock.  Upstream discouraged from wrapping [z]free() by signal queuing globally because it could hide unprotected accesses to the global state and result in wrong behavior (which is actually worse than the deadlock).

The handling of signals is still not perfect even in the latest upstream version of zsh.  See bug #1198671 for the list of related upstream fixes.  Unfortunately, new bug reports are still coming on the upstream mailing list.

Comment 8 Robert Krátký 2016-08-21 15:40:33 UTC

Hi Kamil,

Could you please check the Release Notes text?

Thank you.

Comment 13 errata-xmlrpc 2016-11-03 23:02:21 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-2152.html