We hit an illegal memory access in the zrlock trace point. The problem
is that zrl->zr_owner and zrl->zr_caller are assigned locklessly. And if
zrl->zr_owner got assigned a longer string between when __string()
calculate the strlen, and when __assign_str() does strcpy. The copy will
overflow the buffer.
==
For example:
Initial condition:
zrl->zr_owner = A
zrl->zr_caller = "abc"
Thread A Thread B
-------------------------------------------------
if (zrl->zr_owner == A) {
DTRACE_PROBE2() {
__string() {
strlen(zrl->zr_caller) -> 3
allocate buf[4]
}
zrl->zr_owner = B
zrl->zr_caller = "abcd"
__assign_str() {
strcpy(buf, zrl->zr_caller) <- buffer overflow
==
Dereferencing zrl->zr_owner->pid may also be problematic, in that the
zrl->zr_owner got changed to other task, and that task exits, freeing
the task_struct. This should be very unlikely, as the other task need to
zrl_remove and exit between the dereferencing zr->zr_owner and
zr->zr_owner->pid. Nevertheless, we'll deal with it as well.
To fix the zrl->zr_caller issue, instead of copy the string content, we
just copy the pointer, this is safe because it always points to
__func__, which is static. As for the zrl->zr_owner issue, we pass in
curthread instead of using zrl->zr_owner.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Closes#7291
9470cbd4f9