CVE-2023-53860CVE-2023-53860

In the Linux kernel, the following vulnerability has been resolved: dm: don't attempt to queue IO under RCU protection dm looks up the table for IO based on the request type, with an assumption that if the request is marked REQ_NOWAIT, it's fine to attempt to submit that IO while under RCU read lock protection. This is not OK, as REQ_NOWAIT just means that we should not be sleeping waiting on other IO, it does not mean that we can't potentially schedule. A simple test case demonstrates this quite nicely: int main(int argc, char *argv[]) { struct iovec iov; int fd; fd = open("/dev/dm-0", O_RDONLY | O_DIRECT); posix_memalign(&iov.iov_base, 4096, 4096); iov.iov_len = 4096; preadv2(fd, &iov, 1, 0, RWF_NOWAIT); return 0; } which will instantly spew: BUG: sleeping function called from invalid context at include/linux/sched/mm.h:306 in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 5580, name: dm-nowait preempt_count: 0, expe