In the Linux kernel, the following vulnerability has been resolved: mpls: fix NULL deref in mpls_valid_fib_dump_req() on CONFIG_INET=n On

In the Linux kernel, the following vulnerability has been resolved:

mpls: fix NULL deref in mpls_valid_fib_dump_req() on CONFIG_INET=n

On CONFIG_INET=n builds, mpls_valid_fib_dump_req() walks the parsed
attribute table itself instead of calling ip_valid_fib_dump_req(). The
RTA_OIF arm passes tb[RTA_OIF] to nla_get_u32() without checking it is
present, so an RTM_GETROUTE dump for AF_MPLS with strict checking and no
RTA_OIF hits a NULL dereference.

RTM_GETROUTE is RTNL_KIND_GET, which rtnetlink_rcv_msg() permits without
CAP_NET_ADMIN, so an unprivileged user can trigger it.

Oops: general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:mpls_valid_fib_dump_req (net/mpls/af_mpls.c:2189)
Call Trace:
mpls_dump_routes (net/mpls/af_mpls.c:2236)
netlink_dump (net/netlink/af_netlink.c:2331)
__netlink_dump_start (net/netlink/af_netlink.c:2446)
rtnetlink_rcv_msg (net/core/rtnetlink.c:7033)
netlink_rcv_skb (net/netlink/af_netlink.c:2556)
netlink_unicast (net/netlink/af_netlink.c:1345)
netlink_sendmsg (net/netlink/af_netlink.c:1900)
__sock_sendmsg (net/socket.c:790)
____sys_sendmsg (net/socket.c:2684)
___sys_sendmsg (net/socket.c:2738)
__sys_sendmsg (net/socket.c:2770)
do_syscall_64 (arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)

Skip unset attributes, as ip_valid_fib_dump_req() does.