Bug 75454 - passwd blocks users from entering password information, if other non-root instance of passwd is running.
Summary: passwd blocks users from entering password information, if other non-root ins...
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: pam
Version: 8.0
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Tomas Mraz
QA Contact: Mike McLean
: 99357 (view as bug list)
Depends On:
TreeView+ depends on / blocked
Reported: 2002-10-08 18:41 UTC by Jesse Keating
Modified: 2007-03-27 03:57 UTC (History)
10 users (show)

Clone Of:
Last Closed: 2004-09-16 12:29:28 UTC

Attachments (Terms of Use)
Proposed patch (5.43 KB, patch)
2004-09-08 14:44 UTC, Tomas Mraz
no flags Details | Diff

Description Jesse Keating 2002-10-08 18:41:59 UTC
Description of problem:
If a non-root user runs passwd, this keeps any other non-root users from being
able to run passwd.  This creates a way to block users from changing their
passwords, possible security issue.

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

How reproducible:

Steps to Reproduce:
1. run "passwd" as a non-root user, leave it at the "current password" prompt.
2. as a different, launch "passwd"
3. Observe not getting "Current Password" prompt on second instance of passwd.

Actual Results:  Second instance of passwd will never prompt the user, until the
first instance is finished.

Expected Results:  passwd should allow multiple users to enter data
simultaneously, then provide atomic updates to the actual PAM database.

Additional info:

I was able to reproduce this on a 7.2 machine as well, and this is the oldest
system I have.  I do not know how far back this regresses.

Comment 1 Jesse Keating 2002-10-08 18:50:22 UTC
It also seems that by running "passwd" as a non-root user, it will block root
from being able to run passwd as well.  This seems slightly more severe than at
first glance.

Comment 2 Need Real Name 2002-10-08 18:59:07 UTC
Confirmed in 7.0 and 7.1 too.  Ironically enough, a non-root user can block a
root passwd command , but a root passwd doesn't block a non-root user, at least
from the first prompt.

Comment 3 Miloslav Trmac 2002-10-08 21:45:06 UTC
Well, root can always kill the passwd process and then
remove the /etc/.pwd.lock file.

Comment 4 Josh Bressers 2004-06-21 22:10:10 UTC
Removing security status.  This isn't a security issue.

Comment 5 Tomas Mraz 2004-09-08 13:06:53 UTC
The only way how to do it right is to obtain the lock only for the
real update of the file. However it is necessary to recheck the old
password to disallow possible races.

I'll try to make a patch.

Comment 6 Tomas Mraz 2004-09-08 14:44:05 UTC
Created attachment 103587 [details]
Proposed patch

Comment 7 Tomas Mraz 2004-09-16 12:29:28 UTC
Fixed in pam-0.77-56

Comment 8 Tomas Mraz 2004-09-16 12:32:49 UTC
*** Bug 99357 has been marked as a duplicate of this bug. ***

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