Here is a bug that is present in AIX kernels(?) right from version 5.1 to latest(?) 6.1 and it allows an unprivileged user to execute commands that use high CPU and can’t be killed (kill -9) even by a root user.
Following is easiest way to reproduce the bug.
- Do cat > /tmp/file and let the command run (i.e. don’t input EOF character).
- Next do rm /tmp/file
- Next find the PID of the command execute in step 1, using ps -ef command or in any other way.
- Next execute the following command cat >> /proc/<PID>/fd/1 (replace PID with that found in step 3). And cat gets hung with high CPU usage.
- You can execute as many cat >> /proc/<PID>/fd/1 commands as you want (from another terminal).
Now even root can’t kill any of the cat commands (except for the one in step 1) and all of them continue using high amount of CPU indefinitely or until cat in step 1 exists. An obvious bug with the kernel.
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Tags: 2009, AIX, Computers, Kernel, System, UNIX
Posted by slash_blog
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