Linux Kernel 64bit Personality Handling Local Denial of Service Vulnerability

Risk: Medium
Local: Yes
Remote: No
CWE: CWE-Other

CVSS Base Score: 4.7/10
Impact Subscore: 6.9/10
Exploitability Subscore: 3.4/10
Exploit range: Local
Attack complexity: Medium
Authentication: No required
Confidentiality impact: None
Integrity impact: None
Availability impact: Complete

I found by accident an reliable way to panic the kernel on an x86_64 system. Since this one can be triggered by an unprivileged user I CCed I also haven't found a corresponding bug on So, what to do to trigger the bug: 1. Enable core dumps 2. Start an 32 bit program that tries to execve() an 64 bit program 3. The 64 bit program cannot be started by the kernel because it can't find the interpreter, i.e. execve returns with an error 4. Generate a segmentation fault 5. panic The problem seams to be located in fs/binfmt_elf.c:load_elf_binary(). It calls SET_PERSONALITY() prior checking that the ELF interpreter is available. This in turn makes the previously 32 bit process a 64 bit one which would be fine if execve() would succeed. But after the SET_PERSONALITY() the open_exec() call fails (because it cannot find the interpreter) and execve() almost instantly returns with an error. If you now look at /proc/PID/maps you'll see, that it has the vsyscall page mapped which shouldn't be. But the process is not dead yet, it's still running. By now generating a segmentation fault and in turn trying to generate a core dump the kernel just dies. I haven't yet looked into this code but maybe you guys are much faster than me and just can fix this problem :) Test case for this bug is attached. It was tested on a and, but I may affect even older kernels. So it may be interesting for stable, too. Greetings, Mathias Krause


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