Re: A slab-out-of-bounds Read bug in __htab_map_lookup_and_delete_batch

[Alexei Starovoitov]

On Wed, Dec 29, 2021 at 2:10 AM butt3rflyh4ck
<butterflyhuangxx@xxxxxxxxx> wrote:
>
> Hi, there is a slab-out-bounds Read bug in
> __htab_map_lookup_and_delete_batch in kernel/bpf/hashtab.c
> and I reproduce it in linux-5.16.rc7(upstream) and latest linux-5.15.11.
>
> #carsh log
> [  166.945208][ T6897]
> ==================================================================
> [  166.947075][ T6897] BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x87/0xb0
> [  166.948612][ T6897] Read of size 49 at addr ffff88801913f800 by
> task __htab_map_look/6897
> [  166.950406][ T6897]
> [  166.950890][ T6897] CPU: 1 PID: 6897 Comm: __htab_map_look Not
> tainted 5.16.0-rc7+ #30
> [  166.952521][ T6897] Hardware name: QEMU Standard PC (i440FX + PIIX,
> 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
> [  166.954562][ T6897] Call Trace:
> [  166.955268][ T6897]  <TASK>
> [  166.955918][ T6897]  dump_stack_lvl+0x57/0x7d
> [  166.956875][ T6897]  print_address_description.constprop.0.cold+0x93/0x347
> [  166.958411][ T6897]  ? _copy_to_user+0x87/0xb0
> [  166.959356][ T6897]  ? _copy_to_user+0x87/0xb0
> [  166.960272][ T6897]  kasan_report.cold+0x83/0xdf
> [  166.961196][ T6897]  ? _copy_to_user+0x87/0xb0
> [  166.962053][ T6897]  kasan_check_range+0x13b/0x190
> [  166.962978][ T6897]  _copy_to_user+0x87/0xb0
> [  166.964340][ T6897]  __htab_map_lookup_and_delete_batch+0xdc2/0x1590
> [  166.965619][ T6897]  ? htab_lru_map_update_elem+0xe70/0xe70
> [  166.966732][ T6897]  bpf_map_do_batch+0x1fa/0x460
> [  166.967619][ T6897]  __sys_bpf+0x99a/0x3860
> [  166.968443][ T6897]  ? bpf_link_get_from_fd+0xd0/0xd0
> [  166.969393][ T6897]  ? rcu_read_lock_sched_held+0x9c/0xd0
> [  166.970425][ T6897]  ? lock_acquire+0x1ab/0x520
> [  166.971284][ T6897]  ? find_held_lock+0x2d/0x110
> [  166.972208][ T6897]  ? rcu_read_lock_sched_held+0x9c/0xd0
> [  166.973139][ T6897]  ? rcu_read_lock_bh_held+0xb0/0xb0
> [  166.974096][ T6897]  __x64_sys_bpf+0x70/0xb0
> [  166.974903][ T6897]  ? syscall_enter_from_user_mode+0x21/0x70
> [  166.976077][ T6897]  do_syscall_64+0x35/0xb0
> [  166.976889][ T6897]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> [  166.978027][ T6897] RIP: 0033:0x450f0d
>
>
> In hashtable, if the elements' keys have the same jhash() value, the
> elements will be put into the same bucket.
> By putting a lot of elements into a single bucket, the value of
> bucket_size can be increased to overflow.
>  but also we can increase bucket_cnt to out of bound Read.

Can you be more specific?
If you can send a patch with a fix it would be even better.

> the out of bound Read in  __htab_map_lookup_and_delete_batch code:
> ```
> ...
> if (bucket_cnt && (copy_to_user(ukeys + total * key_size, keys,
> key_size * bucket_cnt) ||
>     copy_to_user(uvalues + total * value_size, values,
>     value_size * bucket_cnt))) {
> ret = -EFAULT;
> goto after_loop;
> }
> ...
> ```
>
> Regards,
>  butt3rflyh4ck.
>
>
> --
> Active Defense Lab of Venustech