Re: [PATCH net] net: prevent NULL pointer dereference in rt_fibinfo_free() and rt_fibinfo_free_cpus()

[Eric Dumazet]

On Tue, Sep 10, 2024 at 5:23 AM Jeongjun Park <aha310510@xxxxxxxxx> wrote:
>
>
> > Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> > On Mon, Sep 9, 2024 at 8:48 PM Jeongjun Park <aha310510@xxxxxxxxx> wrote:
> >>
> >> rt_fibinfo_free() and rt_fibinfo_free_cpus() only check for rt and do not
> >> verify rt->dst and use it, which will result in NULL pointer dereference.
> >>
> >> Therefore, to prevent this, we need to add a check for rt->dst.
> >>
> >> Fixes: 0830106c5390 ("ipv4: take dst->__refcnt when caching dst in fib")
> >> Fixes: c5038a8327b9 ("ipv4: Cache routes in nexthop exception entries.")
> >> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
> >> ---
> >
> > As far as I can tell, your patch is a NOP, and these Fixes: tags seem
> > random to me.
>
> I somewhat agree with the opinion that the fixes tag is random.
> However, I think it is absolutely necessary to add a check for
> &rt->dst , because the existence of rt does not guarantee that
> &rt->dst will not be NULL.
>
> >
> > Also, I am guessing this is based on a syzbot report ?
>
> Yes, but it's not a bug reported to syzbot, it's a bug that
> I accidentally found in my syzkaller fuzzer. The report is too long
> to be included in the patch notes, so I'll attach it to this email.

syzbot has a similar report in its queue, I put it on hold because
this is some unrelated memory corruption.

rt (R14 in your case) is 0x1 at this point, which is not a valid memory pointer.

So I am definitely saying no to your patch.

>
> Report:
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 0 UID: 0 PID: 4694 Comm: systemd-udevd Not tainted 6.11.0-rc6-00326-gd1f2d51b711a #16
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:dst_dev_put+0x26/0x330 net/core/dst.c:149
> Code: 90 90 90 90 f3 0f 1e fa 41 57 41 56 49 89 fe 41 55 41 54 55 e8 0b 90 af f8 4c 89 f2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 da 02 00 00 49 8d 7e 3a 4d 8b 26 48 b8 00 00 00
> RSP: 0018:ffffc90000007d68 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffffff8976519a
> RDX: 0000000000000000 RSI: ffffffff88d97a95 RDI: 0000000000000001
> RBP: dffffc0000000000 R08: 0000000000000001 R09: ffffed100c8020c3
> R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff1ab5a81
> R13: 0000607f8106c5c8 R14: 0000000000000001 R15: 0000000000000000
> FS:  00007f235c5fd8c0(0000) GS:ffff88802c400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f39c90e5168 CR3: 0000000019688000 CR4: 0000000000750ef0
> PKRU: 55555554
> Call Trace:
>  <IRQ>
>  rt_fibinfo_free_cpus.part.0+0xf4/0x1d0 net/ipv4/fib_semantics.c:206
>  rt_fibinfo_free_cpus net/ipv4/fib_semantics.c:198 [inline]
>  fib_nh_common_release+0x121/0x360 net/ipv4/fib_semantics.c:217
>  fib_nh_release net/ipv4/fib_semantics.c:229 [inline]
>  free_fib_info_rcu+0x18f/0x4b0 net/ipv4/fib_semantics.c:241
>  rcu_do_batch kernel/rcu/tree.c:2569 [inline]
>  rcu_core+0x826/0x16d0 kernel/rcu/tree.c:2843
>  handle_softirqs+0x1d4/0x870 kernel/softirq.c:554
>  __do_softirq kernel/softirq.c:588 [inline]
>  invoke_softirq kernel/softirq.c:428 [inline]
>  __irq_exit_rcu kernel/softirq.c:637 [inline]
>  irq_exit_rcu+0xbb/0x120 kernel/softirq.c:649
>  instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
>  sysvec_apic_timer_interrupt+0x99/0xb0 arch/x86/kernel/apic/apic.c:1043
>  </IRQ>
>  <TASK>
>  asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
> RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
> RIP: 0010:_raw_spin_unlock_irqrestore+0x3c/0x70 kernel/locking/spinlock.c:194
> Code: 74 24 10 e8 d6 03 6f f6 48 89 ef e8 8e 77 6f f6 81 e3 00 02 00 00 75 29 9c 58 f6 c4 02 75 35 48 85 db 74 01 fb bf 01 00 00 00 e8 bf 24 61 f6 65 8b 05 c0 79 0b 75 85 c0 74 0e 5b 5d c3 cc cc cc
> RSP: 0018:ffffc90001f978f8 EFLAGS: 00000206
> RAX: 0000000000000006 RBX: 0000000000000200 RCX: 1ffffffff1fe4be9
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000001
> RBP: ffffffff8dbc0ac0 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffffff8ff2a39f R11: ffffffff815d29ca R12: 0000000000000246
> R13: ffff88801e866100 R14: 0000000000000200 R15: 0000000000000000
>  rcu_read_unlock_special kernel/rcu/tree_plugin.h:691 [inline]
>  __rcu_read_unlock+0x2d9/0x580 kernel/rcu/tree_plugin.h:436
>  __netlink_sendskb net/netlink/af_netlink.c:1278 [inline]
>  netlink_broadcast_deliver net/netlink/af_netlink.c:1408 [inline]
>  do_one_broadcast net/netlink/af_netlink.c:1495 [inline]
>  netlink_broadcast_filtered+0x8ec/0xe00 net/netlink/af_netlink.c:1540
>  netlink_broadcast net/netlink/af_netlink.c:1564 [inline]
>  netlink_sendmsg+0x9ee/0xd80 net/netlink/af_netlink.c:1899
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg net/socket.c:745 [inline]
>  ____sys_sendmsg+0xabe/0xc80 net/socket.c:2597
>  ___sys_sendmsg+0x11d/0x1c0 net/socket.c:2651
>  __sys_sendmsg+0xfe/0x1d0 net/socket.c:2680
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcb/0x250 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f235c8b0e13
> Code: 8b 15 b9 a1 00 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 2e 00 00 00 0f 05 48 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 89 54 24 1c 48
> RSP: 002b:00007ffe93910d38 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 0000556a6858ba60 RCX: 00007f235c8b0e13
> RDX: 0000000000000000 RSI: 00007ffe93910d60 RDI: 000000000000000e
> RBP: 0000556a6858bdc0 R08: 00000000ffffffff R09: 0000556a685488e0
> R10: 0000556a6858be38 R11: 0000000000000246 R12: 0000000000008010
> R13: 0000556a6856fc30 R14: 0000000000000000 R15: 00007ffe93910df0
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:dst_dev_put+0x26/0x330 net/core/dst.c:149
> Code: 90 90 90 90 f3 0f 1e fa 41 57 41 56 49 89 fe 41 55 41 54 55 e8 0b 90 af f8 4c 89 f2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 da 02 00 00 49 8d 7e 3a 4d 8b 26 48 b8 00 00 00
> RSP: 0018:ffffc90000007d68 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffffff8976519a
> RDX: 0000000000000000 RSI: ffffffff88d97a95 RDI: 0000000000000001
> RBP: dffffc0000000000 R08: 0000000000000001 R09: ffffed100c8020c3
> R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff1ab5a81
> R13: 0000607f8106c5c8 R14: 0000000000000001 R15: 0000000000000000
> FS:  00007f235c5fd8c0(0000) GS:ffff88802c400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f39c90e5168 CR3: 0000000019688000 CR4: 0000000000750ef0
> PKRU: 55555554
> ----------------
> Code disassembly (best guess):
>    0:   90                      nop
>    1:   90                      nop
>    2:   90                      nop
>    3:   90                      nop
>    4:   f3 0f 1e fa             endbr64
>    8:   41 57                   push   %r15
>    a:   41 56                   push   %r14
>    c:   49 89 fe                mov    %rdi,%r14
>    f:   41 55                   push   %r13
>   11:   41 54                   push   %r12
>   13:   55                      push   %rbp
>   14:   e8 0b 90 af f8          call   0xf8af9024
>   19:   4c 89 f2                mov    %r14,%rdx
>   1c:   48 b8 00 00 00 00 00    movabs $0xdffffc0000000000,%rax
>   23:   fc ff df
>   26:   48 c1 ea 03             shr    $0x3,%rdx
> * 2a:   80 3c 02 00             cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
>   2e:   0f 85 da 02 00 00       jne    0x30e
>   34:   49 8d 7e 3a             lea    0x3a(%r14),%rdi
>   38:   4d 8b 26                mov    (%r14),%r12
>   3b:   48                      rex.W
>   3c:   b8                      .byte 0xb8
>   3d:   00 00                   add    %al,(%rax)