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