CVE-2021-47418

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net_sched: fix NULL deref in fifo_set_limit()<br /> <br /> syzbot reported another NULL deref in fifo_set_limit() [1]<br /> <br /> I could repro the issue with :<br /> <br /> unshare -n<br /> tc qd add dev lo root handle 1:0 tbf limit 200000 burst 70000 rate 100Mbit<br /> tc qd replace dev lo parent 1:0 pfifo_fast<br /> tc qd change dev lo root handle 1:0 tbf limit 300000 burst 70000 rate 100Mbit<br /> <br /> pfifo_fast does not have a change() operation.<br /> Make fifo_set_limit() more robust about this.<br /> <br /> [1]<br /> BUG: kernel NULL pointer dereference, address: 0000000000000000<br /> PGD 1cf99067 P4D 1cf99067 PUD 7ca49067 PMD 0<br /> Oops: 0010 [#1] PREEMPT SMP KASAN<br /> CPU: 1 PID: 14443 Comm: syz-executor959 Not tainted 5.15.0-rc3-syzkaller #0<br /> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011<br /> RIP: 0010:0x0<br /> Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.<br /> RSP: 0018:ffffc9000e2f7310 EFLAGS: 00010246<br /> RAX: dffffc0000000000 RBX: ffffffff8d6ecc00 RCX: 0000000000000000<br /> RDX: 0000000000000000 RSI: ffff888024c27910 RDI: ffff888071e34000<br /> RBP: ffff888071e34000 R08: 0000000000000001 R09: ffffffff8fcfb947<br /> R10: 0000000000000001 R11: 0000000000000000 R12: ffff888024c27910<br /> R13: ffff888071e34018 R14: 0000000000000000 R15: ffff88801ef74800<br /> FS: 00007f321d897700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: ffffffffffffffd6 CR3: 00000000722c3000 CR4: 00000000003506e0<br /> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000<br /> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400<br /> Call Trace:<br /> fifo_set_limit net/sched/sch_fifo.c:242 [inline]<br /> fifo_set_limit+0x198/0x210 net/sched/sch_fifo.c:227<br /> tbf_change+0x6ec/0x16d0 net/sched/sch_tbf.c:418<br /> qdisc_change net/sched/sch_api.c:1332 [inline]<br /> tc_modify_qdisc+0xd9a/0x1a60 net/sched/sch_api.c:1634<br /> rtnetlink_rcv_msg+0x413/0xb80 net/core/rtnetlink.c:5572<br /> netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504<br /> netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]<br /> netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1340<br /> netlink_sendmsg+0x86d/0xdb0 net/netlink/af_netlink.c:1929<br /> sock_sendmsg_nosec net/socket.c:704 [inline]<br /> sock_sendmsg+0xcf/0x120 net/socket.c:724<br /> ____sys_sendmsg+0x6e8/0x810 net/socket.c:2409<br /> ___sys_sendmsg+0xf3/0x170 net/socket.c:2463<br /> __sys_sendmsg+0xe5/0x1b0 net/socket.c:2492<br /> do_syscall_x64 arch/x86/entry/common.c:50 [inline]<br /> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80<br /> entry_SYSCALL_64_after_hwframe+0x44/0xae