Red Hat Bugzilla – Bug 144361
CAN-2004-1074 a.out binfmt DoS
Last modified: 2007-11-30 17:07:05 EST
From the lkml mailing list. http://www.ussg.iu.edu/hypermail/linux/kernel/0411.1/1222.html It is possible that an improperly formed a.out binary can cause a kernel-oops, which if executed in a loop will ead fd's and memory. It seems that you have to turn on memory overcommit on for this to work. davej says we didn't enable a.out binaries on FC3 and RHEL4. This will be undone in the future though. We do not turn on memory overcommit by default in RHEL2.1 or 3. This should make the impact of this issue significantly mitigated since it seems the issue is only exploitable when overcommit is on (sysctl -w vm.overcommit_memory=1). However note that we do tell customers how to turn this on. fixed=2.6.10 (20041116 cset@419aaba8xdR0decwoMnVpt3G8_f8kQ) not fixed for 2.4 (as at Nov24) Patch: http://www.ussg.iu.edu/hypermail/linux/kernel/0411.1/1290.html
I cannot reproduce this problem. > try executing this binary: > perl -e'print"\x07\x01".("\x00"x13)."\xc0".("\x00"x16)'>eout > (it may be neccessary to turn memory overcommit on before) > > This should result in a kernel-oops. > Doing this in a loop will eat fd's and memory. I've loaded the binfmt_aout module, and set vm.overcommit_memory, and created the binary using the supplied perl script: # uname -r 2.4.21-27.ELsmp # lsmod | grep binfmt binfmt_aout 5440 0 # sysctl -w vm.overcommit_memory=1 vm.overcommit_memory = 1 # perl -e'print"\x07\x01".("\x00"x13)."\xc0".("\x00"x16)'>eout # file eout eout: 386 executable not stripped # chmod +x eout # while true > do > ./eout > done -bash: ./eout: cannot execute binary file -bash: ./eout: cannot execute binary file -bash: ./eout: cannot execute binary file -bash: ./eout: cannot execute binary file ... # strace ./eout strace: exec: Exec format error execve("./eout", ["./eout"], [/* 30 vars */]) = 0 #
See http://linux.bkbits.net:8080/linux-2.4/cset@41c36fb6q1Z68WUzKQFjJR-40Ev3tw for the backported fix Removing [kernel-unsupported] since this allegedly will also affect elf binaries on ia64 etc.
How can it be reproduced with an ELF binary on an ia64?
I've determined that this was fixed in U5 (in kernel version 2.4.21-27.8.EL) as well as in the 2nd E5 build (in kernel version 2.4.21-27.0.2.EL). Here is the comment associated with the release of that E5 advisory: "An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2005-043.html" Obviously, we'd rather have people upgrade to U5 at this point, which was released with advisory RHSA-2005:294.
*** Bug 144153 has been marked as a duplicate of this bug. ***