Red Hat Bugzilla – Bug 75454
passwd blocks users from entering password information, if other non-root instance of passwd is running.
Last modified: 2007-03-26 23:57:34 EDT
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: Always 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.
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.
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.
Well, root can always kill the passwd process and then remove the /etc/.pwd.lock file.
Removing security status. This isn't a security issue.
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.
Created attachment 103587 [details] Proposed patch
Fixed in pam-0.77-56
*** Bug 99357 has been marked as a duplicate of this bug. ***