CVE-2024-36902

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

ipv6: fib6_rules: avoid possible NULL dereference in fib6_rule_action()

syzbot is able to trigger the following crash [1], caused by unsafe ip6_dst_idev() use.

Indeed ip6_dst_idev() can return NULL, and must always be checked.

[1]

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 0 PID: 31648 Comm: syz-executor.0 Not tainted 6.9.0-rc4-next-20240417-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 RIP: 0010:__fib6_rule_action net/ipv6/fib6_rules.c:237 [inline] RIP: 0010:fib6_rule_action+0x241/0x7b0 net/ipv6/fib6_rules.c:267 Code: 02 00 00 49 8d 9f d8 00 00 00 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 f9 32 bf f7 48 8b 1b 48 89 d8 48 c1 e8 03 <42> 80 3c 20 00 74 08 48 89 df e8 e0 32 bf f7 4c 8b 03 48 89 ef 4c RSP: 0018:ffffc9000fc1f2f0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1a772f98c8186700 RDX: 0000000000000003 RSI: ffffffff8bcac4e0 RDI: ffffffff8c1f9760 RBP: ffff8880673fb980 R08: ffffffff8fac15ef R09: 1ffffffff1f582bd R10: dffffc0000000000 R11: fffffbfff1f582be R12: dffffc0000000000 R13: 0000000000000080 R14: ffff888076509000 R15: ffff88807a029a00 FS: 00007f55e82ca6c0(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b31d23000 CR3: 0000000022b66000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: fib_rules_lookup+0x62c/0xdb0 net/core/fib_rules.c:317 fib6_rule_lookup+0x1fd/0x790 net/ipv6/fib6_rules.c:108 ip6_route_output_flags_noref net/ipv6/route.c:2637 [inline] ip6_route_output_flags+0x38e/0x610 net/ipv6/route.c:2649 ip6_route_output include/net/ip6_route.h:93 [inline] ip6_dst_lookup_tail+0x189/0x11a0 net/ipv6/ip6_output.c:1120 ip6_dst_lookup_flow+0xb9/0x180 net/ipv6/ip6_output.c:1250 sctp_v6_get_dst+0x792/0x1e20 net/sctp/ipv6.c:326 sctp_transport_route+0x12c/0x2e0 net/sctp/transport.c:455 sctp_assoc_add_peer+0x614/0x15c0 net/sctp/associola.c:662 sctp_connect_new_asoc+0x31d/0x6c0 net/sctp/socket.c:1099 __sctp_connect+0x66d/0xe30 net/sctp/socket.c:1197 sctp_connect net/sctp/socket.c:4819 [inline] sctp_inet_connect+0x149/0x1f0 net/sctp/socket.c:4834 __sys_connect_file net/socket.c:2048 [inline] __sys_connect+0x2df/0x310 net/socket.c:2065 __do_sys_connect net/socket.c:2075 [inline] __se_sys_connect net/socket.c:2072 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:2072 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/1876881c9a49613b5249fb400cbf53412d90cb09
• https://git.kernel.org/stable/c/35297fc68de36826087e976f86a5b1f94fd0bf95
• https://git.kernel.org/stable/c/4a5a573387da6a6b23a4cc62147453ff1bc32afa
• https://git.kernel.org/stable/c/674c951ab8a23f7aff9b4c3f2f865901bc76a290
• https://git.kernel.org/stable/c/7e3242c139c38e60844638e394c2877b16b396b0
• https://git.kernel.org/stable/c/8745a8d74ba17dafe72b6ab461fa6c007d879747
• https://git.kernel.org/stable/c/d101291b2681e5ab938554e3e323f7a7ee33e3aa
• https://git.kernel.org/stable/c/ddec23f206a944c73bcc2724358b85388837daff
• https://lists.debian.org/debian-lts-announce/2024/06/msg00019.html
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html