CVE-2021-47297

In the Linux kernel, the following vulnerability has been resolved: net:
fix uninit-value in caif_seqpkt_sendmsg When nr_segs equal to zero in
iovec_from_user, the object msg->msg_iter.iov is uninit stack memory in
caif_seqpkt_sendmsg which is defined in ___sys_sendmsg. So we cann’t just
judge msg->msg_iter.iov->base directlly. We can use nr_segs to judge msg in
caif_seqpkt_sendmsg whether has data buffers.
===================================================== BUG: KMSAN:
uninit-value in caif_seqpkt_sendmsg+0x693/0xf60 net/caif/caif_socket.c:542
Call Trace: __dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x220 lib/dump_stack.c:118 kmsan_report+0xf7/0x1e0
mm/kmsan/kmsan_report.c:118 __msan_warning+0x58/0xa0
mm/kmsan/kmsan_instr.c:215 caif_seqpkt_sendmsg+0x693/0xf60
net/caif/caif_socket.c:542 sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg net/socket.c:672 [inline] ____sys_sendmsg+0x12b6/0x1350
net/socket.c:2343 ___sys_sendmsg net/socket.c:2397 [inline]
__sys_sendmmsg+0x808/0xc90 net/socket.c:2480 __compat_sys_sendmmsg
net/compat.c:656 [inline]