In the Linux kernel, the following vulnerability has been resolved:
rseq: Fix using an uninitialized stack variable in rseq_exit_user_update()
There is an bug in which an uninitialized stack variable is used in
rseq_exit_user_update() as reported by syzbot:
BUG: KMSAN: kernel-infoleak in rseq_set_ids_get_csaddr include/linux/rseq_entry.h:502 [inline]
The local variable:
<pre>
struct rseq_ids ids = {
.cpu_id = task_cpu(t),
.mm_cid = task_mm_cid(t),
.node_id = cpu_to_node(ids.cpu_id),
};
</pre>
According to the C standard, the evaluation order of expressions in an
initializer list is indeterminately sequenced. The compiler (Clang, in
this KMSAN build) evaluates cpu_to_node(ids.cpu_id) before
ids.cpu_id is initialized with task_cpu(t).
This is fixed by moving the assignment of ids.node_id outside the
structure initialization.