CVE: CVE-2024-56646
Published: 2024-12-27
Description: In the Linux kernel, the following vulnerability has been resolved:

ipv6: avoid possible NULL deref in modify_prefix_route()

syzbot found a NULL deref [1] in modify_prefix_route(), caused by one
fib6_info without a fib6_table pointer set.

This can happen for net->ipv6.fib6_null_entry

[1]
Oops: general protection fault, probably for non-canonical address 0xdffffc[PII_REDACTED]: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x[PII_REDACTED]000030-0x[PII_REDACTED]000037]
CPU: 1 UID: 0 PID: 5837 Comm: syz-executor888 Not tainted 6.12.0-syzkaller-09567-g7eef7e306d3c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
 RIP: 0010:__lock_acquire+0xe4/0x3c40 kernel/locking/lockdep.c:5089
Code: 08 84 d2 0f 85 15 14 00 00 44 8b 0d ca 98 f5 0e 45 85 c9 0f 84 b4 0e 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 0f 85 96 2c 00 00 49 8b 04 24 48 3d a0 07 7f 93 0f 84
RSP: 0018:ffffc900035d7268 EFLAGS: 00010006
RAX: dffffc[PII_REDACTED] RBX: [PII_REDACTED] RCX: [PII_REDACTED]
RDX: [PII_REDACTED] RSI: 1ffff920006bae5f RDI: [PII_REDACTED]
RBP: [PII_REDACTED] R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: ffffffff90608e17 R11: [PII_REDACTED] R12: [PII_REDACTED]
R13: ffff[PII_REDACTED]80 R14: [PII_REDACTED] R15: [PII_REDACTED]
FS: [PII_REDACTED]e90380(0000) GS:ffff8880b8700000(0000) knlGS:[PII_REDACTED]
CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2: 00007ffc59cc4278 CR3:[PII_REDACTED]b54000 CR4:[PII_REDACTED]3526f0
DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
Call Trace:
 <TASK>
  lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5849
  __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
  _raw_spin_lock_bh+0x33/0x40 kernel/locking/spinlock.c:178
  spin_lock_bh include/linux/spinlock.h:356 [inline]
  modify_prefix_route+0x30b/0x8b0 net/ipv6/addrconf.c:4831
  inet6_addr_modify net/ipv6/addrconf.c:4923 [inline]
  inet6_rtm_newaddr+0x12c7/0x1ab0 net/ipv6/addrconf.c:5055
  rtnetlink_rcv_msg+0x3c7/0xea0 net/core/rtnetlink.c:6920
  netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2541
  netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
  netlink_unicast+0x53c/0x7f0 net/netlink/af_netlink.c:1347
  netlink_sendmsg+0x8b8/0xd70 net/netlink/af_netlink.c:1891
  sock_sendmsg_nosec net/socket.c:711 [inline]
  __sock_sendmsg net/socket.c:726 [inline]
  ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2583
  ___sys_sendmsg+0x135/0x1e0 net/socket.c:2637
  __sys_sendmsg+0x16e/0x220 net/socket.c:2669
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd1dcef8b79
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc59cc4378 EFLAGS: 00000246 ORIG_RAX:[PII_REDACTED]00002e
RAX: ffffffffffffffda RBX: [PII_REDACTED] RCX: 00007fd1dcef8b79
RDX: [PII_REDACTED] RSI: [PII_REDACTED] RDI: [PII_REDACTED]
RBP:[PII_REDACTED]0113fd R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: 00007ffc59cc438c
R13: 431bde82d7b634db R14: [PII_REDACTED] R15: [PII_REDACTED]
 </TASK>
CVSS Score: 5.5 (MEDIUM)
CWE: CWE-476, CWE-476
References: https://git.kernel.org/stable/c/01f95357e47219a9c4b29e177b717edbfab721b4; https://git.kernel.org/stable/c/90f7d995b861fd77ae4885cc58e26a6a4e5ccdb9; https://git.kernel.org/stable/c/a747e02430dfb3657141f99aa6b09331283fa493