Bug 447 – sudo hangs - race condition if SIGCHLD is received immediately before we call select()

Bug 447 - sudo hangs - race condition if SIGCHLD is received immediately before we call select()


Summary:	sudo hangs - race condition if SIGCHLD is received immediately before we call...

Status:	RESOLVED FIXED

Product:	Sudo
Classification:	Unclassified
Component:	Sudo
Version:	1.7.4
Hardware:	PC Linux

Importance:	low normal
Assigned To:	Todd C. Miller

URL:

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2010-11-01 17:10 MDT by Ivan Zahariev (famzah)
Modified:	2011-03-03 09:53 MST (History)
CC List:	0 users

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Description Ivan Zahariev (famzah) 2010-11-01 17:10:32 MDT

Sometimes sudo enters in an endless blocking state and never exits. The called program finishes successfully, but is left in "zombie" state.

You have already tried to fix this by http://www.sudo.ws/repos/sudo/rev/99adc5ea7f0a . However, there's always a possibility that SIGCHLD arrives right after the "if" and just before the "select()". In order to fix this, the blocking select() must be used with a "timeout" (say one second or less). This bug is usually rarely encountered on busy systems.

More details on the bug and a proposed fix can be found at my blog article about it: http://blog.famzah.net/2010/11/01/sudo-hangs-and-leaves-the-executed-program-as-zombie/

P.S. Select() is used at least at two places, so they probably should both be fixed.

Comment 1 Todd C. Miller 2010-11-01 17:41:16 MDT

This should be fixed in sudo 1.7.5 which uses a pipe for signal delivery, eliminating the race condition.  I'll have a beta release of 1.7.5 out soon.

Comment 2 Todd C. Miller 2010-11-03 13:31:19 MDT

THe first beta of sudo 1.7.5 is out now.
http://www.sudo.ws/sudo/dist/beta/sudo-1.7.5b1.tar.gz

Comment 3 Todd C. Miller 2011-03-03 09:53:28 MST

Fixed in sudo 1.7.5 and 1.8.0.