Re: [PATCH net] ipv6: avoid possible NULL deref in modify_prefix_route()

[David Ahern <dsahern@kernel.org>]

On 11/26/24 12:28 PM, Eric Dumazet wrote:
> 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 0xdffffc0000000006: 0000 [#1] PREEMPT SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
> 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: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000006 RSI: 1ffff920006bae5f RDI: 0000000000000030
> RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffffff90608e17 R11: 0000000000000001 R12: 0000000000000030
> R13: ffff888036334880 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000555579e90380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffc59cc4278 CR3: 0000000072b54000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 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: 000000000000002e
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fd1dcef8b79
> RDX: 0000000000040040 RSI: 0000000020000140 RDI: 0000000000000004
> RBP: 00000000000113fd R08: 0000000000000006 R09: 0000000000000006
> R10: 0000000000000006 R11: 0000000000000246 R12: 00007ffc59cc438c
> R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> 
> Fixes: 5eb902b8e719 ("net/ipv6: Remove expired routes with a separated list of routes.")
> Reported-by: syzbot+1de74b0794c40c8eb300@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/67461f7f.050a0220.1286eb.0021.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> CC: Kui-Feng Lee <thinker.li@gmail.com>
> Cc: David Ahern <dsahern@kernel.org>
> ---
>  net/ipv6/addrconf.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>