CVE-2018-14634

Red Hat statement

This issue does not affect 32-bit systems as they do not have a large enough address space to exploit this flaw. Systems with less than 32GB of memory are very unlikely to be affected by this issue due to memory demands during exploitation. This issue does not affect the versions of Linux kernel as shipped with Red Hat Enterprise Linux 5. This issue affects the version of the kernel packages as shipped with Red Hat Enterprise Linux 6, 7 and Red Hat Enterprise MRG 2. Future kernel updates for Red Hat Enterprise Linux 6, 7 and Red Hat Enterprise MRG 2 will address this issue.

Red Hat mitigation

To mitigate the issue: Enable and install kernel-debuginfo packages as per https://access.redhat.com/solutions/666123 1) On the host, save the following in a file with the ".stp" extension: // CVE-2018-14634 // // Theory of operations: adjust the thread's # rlimit-in-effect around // calls to the vulnerable get_arg_page() function so as to encompass // the newly required _STK_LIM / 4 * 3 maximum. // Complication: the rlimit is stored in a current-> structure that // is shared across the threads of the process. They may concurrently // invoke this operation. function clamp_stack_rlim_cur:long () %{ struct rlimit *rlim = current->signal->rlim; unsigned long rlim_cur = READ_ONCE(rlim[RLIMIT_STACK].rlim_cur); unsigned long limit = _STK_LIM / 4 * 3; limit *= 4; // multiply it back up, to the scale used by rlim_cur if (rlim_cur > limit) { WRITE_ONCE(rlim[RLIMIT_STACK].rlim_cur, limit); STAP_RETURN(limit); } else STAP_RETURN(0); %} probe kernel.function("copy_strings").call { l = clamp_stack_rlim_cur() if (l) printf("lowered process %s(%d) STACK rlim_cur to %p\n", execname(), pid(), l) } probe begin { printf("CVE-2018-14634 mitigation loaded\n") } probe end { printf("CVE-2018-14634 mitigation unloaded\n") } 2) Install the "systemtap" package and any required dependencies. Refer to the "2. Using SystemTap" chapter in the Red Hat Enterprise Linux "SystemTap Beginners Guide" document, available from docs.redhat.com, for information on installing the required -debuginfo and matching kernel-devel packages 3) Run the "stap -g [filename-from-step-1].stp" command as root. If the host is rebooted, the changes will be lost and the script must be run again. Alternatively, build the systemtap script on a development system with "stap -g -p 4 [filename-from-step-1].stp", distribute the resulting kernel module to all affected systems, and run "staprun -L <module>" on those. When using this approach only systemtap-runtime package is required on the affected systems. Please notice that the kernel version must be the same across all systems. This may not be a suitable workaround if your application uses massive amounts of stack space. Please consider this if there are any adverse affects when running this mitigation.