CVE-2022-50255

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix reading strings from synthetic events

The follow commands caused a crash:

cd /sys/kernel/tracing

echo 's:open char file[]' > dynamic_events

echo 'hist:keys=common_pid:file=filename:onchange($file).trace(open,$file)' > events/syscalls/sys_enter_openat/trigger'

echo 1 > events/synthetic/open/enable

BOOM!

The problem is that the synthetic event field "char file[]" will read the value given to it as a string without any memory checks to make sure the address is valid. The above example will pass in the user space address and the sythetic event code will happily call strlen() on it and then strscpy() where either one will cause an oops when accessing user space addresses.

Use the helper functions from trace_kprobe and trace_eprobe that can read strings safely (and actually succeed when the address is from user space and the memory is mapped in).

Now the above can show:

 packagekitd-1721    [000] ...2.   104.597170: open: file=/usr/lib/rpm/fileattrs/cmake.attr
in:imjournal-978     [006] ...2.   104.599642: open: file=/var/lib/rsyslog/imjournal.state.tmp
 packagekitd-1721    [000] ...2.   104.626308: open: file=/usr/lib/rpm/fileattrs/debuginfo.attr

The synthetic tracing event code read strings via raw kernel dereferences (e.g., strlen/copy) from user-supplied pointers, which can fault in kernel context and crash the system.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.