Subject: Re: [PATCH] bpf, cpumap: Fix use after free of bpf_cpu_map_entry in cpu_map_enqueue

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Fri, 26 Jul 2024 20:55:54 +0200

Radoslaw Zielonek <[email-masked]> writes:

> When cpu_map has been redirected, first the pointer to the
> bpf_cpu_map_entry has been copied, then freed, and read from the copy.
> To fix it, this commit introduced the refcount cpu_map_parent during
> redirections to prevent use after free.
>
> syzbot reported:
>
> [   61.581464][T11670] ==================================================================
> [   61.583323][T11670] BUG: KASAN: slab-use-after-free in cpu_map_enqueue+0xba/0x370
> [   61.585419][T11670] Read of size 8 at addr ffff888122d75208 by task syzbot-repro/11670
> [   61.587541][T11670]
> [   61.588237][T11670] CPU: 1 PID: 11670 Comm: syzbot-repro Not tainted 6.9.0-rc6-00053-g0106679839f7 #27
> [   61.590542][T11670] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.1 11/11/2019
> [   61.592798][T11670] Call Trace:
> [   61.593885][T11670]  <TASK>
> [   61.594805][T11670]  dump_stack_lvl+0x241/0x360
> [   61.595974][T11670]  ? tcp_gro_dev_warn+0x260/0x260
> [   61.598242][T11670]  ? __wake_up_klogd+0xcc/0x100
> [   61.599407][T11670]  ? panic+0x850/0x850
> [   61.600516][T11670]  ? __virt_addr_valid+0x182/0x510
> [   61.602073][T11670]  ? __virt_addr_valid+0x182/0x510
> [   61.603496][T11670]  print_address_description+0x7b/0x360
> [   61.605170][T11670]  print_report+0xfd/0x210
> [   61.606370][T11670]  ? __virt_addr_valid+0x182/0x510
> [   61.607925][T11670]  ? __virt_addr_valid+0x182/0x510
> [   61.609577][T11670]  ? __virt_addr_valid+0x43d/0x510
> [   61.610948][T11670]  ? __phys_addr+0xb9/0x170
> [   61.612103][T11670]  ? cpu_map_enqueue+0xba/0x370
> [   61.613448][T11670]  kasan_report+0x143/0x180
> [   61.615000][T11670]  ? cpu_map_enqueue+0xba/0x370
> [   61.616181][T11670]  cpu_map_enqueue+0xba/0x370
> [   61.617620][T11670]  xdp_do_redirect+0x685/0xbf0
> [   61.618787][T11670]  tun_xdp_act+0xe7/0x9e0
> [   61.619856][T11670]  ? __tun_build_skb+0x2e0/0x2e0
> [   61.621356][T11670]  tun_build_skb+0xac6/0x1140
> [   61.622602][T11670]  ? tun_build_skb+0xb4/0x1140
> [   61.623880][T11670]  ? tun_get_user+0x2760/0x2760
> [   61.625341][T11670]  tun_get_user+0x7fa/0x2760
> [   61.626532][T11670]  ? rcu_read_unlock+0xa0/0xa0
> [   61.627725][T11670]  ? tun_get+0x1e/0x2f0
> [   61.629147][T11670]  ? tun_get+0x1e/0x2f0
> [   61.630265][T11670]  ? tun_get+0x27d/0x2f0
> [   61.631486][T11670]  tun_chr_write_iter+0x111/0x1f0
> [   61.632855][T11670]  vfs_write+0xa84/0xcb0
> [   61.634185][T11670]  ? __lock_acquire+0x1f60/0x1f60
> [   61.635501][T11670]  ? kernel_write+0x330/0x330
> [   61.636757][T11670]  ? lockdep_hardirqs_on_prepare+0x43c/0x780
> [   61.638445][T11670]  ? __fget_files+0x3ea/0x460
> [   61.639448][T11670]  ? seqcount_lockdep_reader_access+0x157/0x220
> [   61.641217][T11670]  ? __fdget_pos+0x19e/0x320
> [   61.642426][T11670]  ksys_write+0x19f/0x2c0
> [   61.643576][T11670]  ? __ia32_sys_read+0x90/0x90
> [   61.644841][T11670]  ? ktime_get_coarse_real_ts64+0x10b/0x120
> [   61.646549][T11670]  do_syscall_64+0xec/0x210
> [   61.647832][T11670]  entry_SYSCALL_64_after_hwframe+0x67/0x6f
> [   61.649485][T11670] RIP: 0033:0x472a4f
> [   61.650539][T11670] Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 c9 d8 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 0c d9 02 00 48
> [   61.655476][T11670] RSP: 002b:00007f7a7a90f5c0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
> [   61.657675][T11670] RAX: ffffffffffffffda RBX: 00007f7a7a911640 RCX: 0000000000472a4f
> [   61.659658][T11670] RDX: 0000000000000066 RSI: 0000000020000440 RDI: 00000000000000c8
> [   61.661980][T11670] RBP: 00007f7a7a90f620 R08: 0000000000000000 R09: 0000000100000000
> [   61.663982][T11670] R10: 0000000100000000 R11: 0000000000000293 R12: 00007f7a7a911640
> [   61.666425][T11670] R13: 000000000000006e R14: 000000000042f2f0 R15: 00007f7a7a8f1000
> [   61.668443][T11670]  </TASK>
> [   61.669233][T11670]
> [   61.669754][T11670] Allocated by task 11643:
> [   61.670855][T11670]  kasan_save_track+0x3f/0x70
> [   61.672094][T11670]  __kasan_kmalloc+0x98/0xb0
> [   61.673466][T11670]  __kmalloc_node+0x259/0x4f0
> [   61.674687][T11670]  bpf_map_kmalloc_node+0xd3/0x1c0
> [   61.676069][T11670]  cpu_map_update_elem+0x2f0/0x1000
> [   61.677619][T11670]  bpf_map_update_value+0x1b2/0x540
> [   61.679006][T11670]  map_update_elem+0x52f/0x6e0
> [   61.680076][T11670]  __sys_bpf+0x7a9/0x850
> [   61.681610][T11670]  __x64_sys_bpf+0x7c/0x90
> [   61.682772][T11670]  do_syscall_64+0xec/0x210
> [   61.683967][T11670]  entry_SYSCALL_64_after_hwframe+0x67/0x6f
> [   61.685648][T11670]
> [   61.686282][T11670] Freed by task 1064:
> [   61.687296][T11670]  kasan_save_track+0x3f/0x70
> [   61.688498][T11670]  kasan_save_free_info+0x40/0x50
> [   61.689786][T11670]  poison_slab_object+0xa6/0xe0
> [   61.691059][T11670]  __kasan_slab_free+0x37/0x60
> [   61.692336][T11670]  kfree+0x136/0x2f0
> [   61.693549][T11670]  __cpu_map_entry_free+0x6f3/0x770
> [   61.695004][T11670]  cpu_map_free+0xc0/0x180
> [   61.696191][T11670]  bpf_map_free_deferred+0xe3/0x100
> [   61.697703][T11670]  process_scheduled_works+0x9cb/0x14a0
> [   61.699330][T11670]  worker_thread+0x85c/0xd50
> [   61.700546][T11670]  kthread+0x2ef/0x390
> [   61.701791][T11670]  ret_from_fork+0x4d/0x80
> [   61.702942][T11670]  ret_from_fork_asm+0x11/0x20
> [   61.704195][T11670]
> [   61.704825][T11670] The buggy address belongs to the object at ffff888122d75200
> [   61.704825][T11670]  which belongs to the cache kmalloc-cg-256 of size 256
> [   61.708516][T11670] The buggy address is located 8 bytes inside of
> [   61.708516][T11670]  freed 256-byte region [ffff888122d75200, ffff888122d75300)
> [   61.712215][T11670]
> [   61.712824][T11670] The buggy address belongs to the physical page:
> [   61.714883][T11670] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x122d74
> [   61.717300][T11670] head: order:1 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> [   61.719037][T11670] memcg:ffff888120d85f01
> [   61.720006][T11670] flags: 0x17ff00000000840(slab|head|node=0|zone=2|lastcpupid=0x7ff)
> [   61.722181][T11670] page_type: 0xffffffff()
> [   61.723318][T11670] raw: 017ff00000000840 ffff88810004dcc0 dead000000000122 0000000000000000
> [   61.725650][T11670] raw: 0000000000000000 0000000080100010 00000001ffffffff ffff888120d85f01
> [   61.727943][T11670] head: 017ff00000000840 ffff88810004dcc0 dead000000000122 0000000000000000
> [   61.730237][T11670] head: 0000000000000000 0000000080100010 00000001ffffffff ffff888120d85f01
> [   61.732671][T11670] head: 017ff00000000001 ffffea00048b5d01 dead000000000122 00000000ffffffff
> [   61.735029][T11670] head: 0000000200000000 0000000000000000 00000000ffffffff 0000000000000000
> [   61.737400][T11670] page dumped because: kasan: bad access detected
> [   61.740100][T11670] page_owner tracks the page as allocated
> [   61.743121][T11670] page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8343, tgid -2092279795 (syzbot-repro), ts 8343, free_ts 43505720198
> [   61.754038][T11670]  post_alloc_hook+0x1e6/0x210
> [   61.756046][T11670]  get_page_from_freelist+0x7d2/0x850
> [   61.759460][T11670]  __alloc_pages+0x25e/0x580
> [   61.761428][T11670]  alloc_slab_page+0x6b/0x1a0
> [   61.764199][T11670]  allocate_slab+0x5d/0x200
> [   61.766122][T11670]  ___slab_alloc+0xac5/0xf20
> [   61.767195][T11670]  __kmalloc+0x2e0/0x4b0
> [   61.769028][T11670]  fib_default_rule_add+0x4a/0x350
> [   61.770394][T11670]  fib6_rules_net_init+0x42/0x100
> [   61.771731][T11670]  ops_init+0x39d/0x670
> [   61.773061][T11670]  setup_net+0x3bc/0xae0
> [   61.774102][T11670]  copy_net_ns+0x399/0x5e0
> [   61.775628][T11670]  create_new_namespaces+0x4de/0x8d0
> [   61.776950][T11670]  unshare_nsproxy_namespaces+0x127/0x190
> [   61.778352][T11670]  ksys_unshare+0x5e6/0xbf0
> [   61.779741][T11670]  __x64_sys_unshare+0x38/0x40
> [   61.781302][T11670] page last free pid 4619 tgid 4619 stack trace:
> [   61.783542][T11670]  free_unref_page_prepare+0x72f/0x7c0
> [   61.785018][T11670]  free_unref_page+0x37/0x3f0
> [   61.786030][T11670]  __slab_free+0x351/0x3f0
> [   61.786991][T11670]  qlist_free_all+0x60/0xd0
> [   61.788827][T11670]  kasan_quarantine_reduce+0x15a/0x170
> [   61.789951][T11670]  __kasan_slab_alloc+0x23/0x70
> [   61.790999][T11670]  kmem_cache_alloc_node+0x193/0x390
> [   61.792331][T11670]  kmalloc_reserve+0xa7/0x2a0
> [   61.793345][T11670]  __alloc_skb+0x1ec/0x430
> [   61.794435][T11670]  netlink_sendmsg+0x615/0xc80
> [   61.796439][T11670]  __sock_sendmsg+0x21f/0x270
> [   61.797467][T11670]  ____sys_sendmsg+0x540/0x860
> [   61.798505][T11670]  __sys_sendmsg+0x2b7/0x3a0
> [   61.799512][T11670]  do_syscall_64+0xec/0x210
> [   61.800674][T11670]  entry_SYSCALL_64_after_hwframe+0x67/0x6f
> [   61.802021][T11670]
> [   61.802526][T11670] Memory state around the buggy address:
> [   61.803701][T11670]  ffff888122d75100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [   61.805694][T11670]  ffff888122d75180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [   61.808104][T11670] >ffff888122d75200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [   61.809769][T11670]                       ^
> [   61.810672][T11670]  ffff888122d75280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [   61.812532][T11670]  ffff888122d75300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [   61.814846][T11670] ==================================================================
> [   61.816914][T11670] Kernel panic - not syncing: KASAN: panic_on_warn set ...
> [   61.818415][T11670] CPU: 1 PID: 11670 Comm: syzbot-repro Not tainted 6.9.0-rc6-00053-g0106679839f7 #27
> [   61.821191][T11670] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.1 11/11/2019
> [   61.822911][T11670] Call Trace:
> [   61.823632][T11670]  <TASK>
> [   61.824525][T11670]  dump_stack_lvl+0x241/0x360
> [   61.825545][T11670]  ? tcp_gro_dev_warn+0x260/0x260
> [   61.826706][T11670]  ? panic+0x850/0x850
> [   61.828594][T11670]  ? lock_release+0x85/0x860
> [   61.829749][T11670]  ? vscnprintf+0x5d/0x80
> [   61.830951][T11670]  panic+0x335/0x850
> [   61.832316][T11670]  ? check_panic_on_warn+0x21/0xa0
> [   61.834475][T11670]  ? __memcpy_flushcache+0x2c0/0x2c0
> [   61.835809][T11670]  ? _raw_spin_unlock_irqrestore+0xd8/0x140
> [   61.838063][T11670]  ? _raw_spin_unlock_irqrestore+0xdd/0x140
> [   61.842056][T11670]  ? _raw_spin_unlock+0x40/0x40
> [   61.843116][T11670]  ? print_report+0x1cc/0x210
> [   61.844527][T11670]  check_panic_on_warn+0x82/0xa0
> [   61.845336][T11670]  ? cpu_map_enqueue+0xba/0x370
> [   61.846117][T11670]  end_report+0x48/0xa0
> [   61.846790][T11670]  kasan_report+0x154/0x180
> [   61.847520][T11670]  ? cpu_map_enqueue+0xba/0x370
> [   61.848471][T11670]  cpu_map_enqueue+0xba/0x370
> [   61.849968][T11670]  xdp_do_redirect+0x685/0xbf0
> [   61.850994][T11670]  tun_xdp_act+0xe7/0x9e0
> [   61.851703][T11670]  ? __tun_build_skb+0x2e0/0x2e0
> [   61.852598][T11670]  tun_build_skb+0xac6/0x1140
> [   61.853362][T11670]  ? tun_build_skb+0xb4/0x1140
> [   61.854454][T11670]  ? tun_get_user+0x2760/0x2760
> [   61.855806][T11670]  tun_get_user+0x7fa/0x2760
> [   61.856734][T11670]  ? rcu_read_unlock+0xa0/0xa0
> [   61.857502][T11670]  ? tun_get+0x1e/0x2f0
> [   61.858171][T11670]  ? tun_get+0x1e/0x2f0
> [   61.858952][T11670]  ? tun_get+0x27d/0x2f0
> [   61.859637][T11670]  tun_chr_write_iter+0x111/0x1f0
> [   61.860913][T11670]  vfs_write+0xa84/0xcb0
> [   61.861578][T11670]  ? __lock_acquire+0x1f60/0x1f60
> [   61.862376][T11670]  ? kernel_write+0x330/0x330
> [   61.863221][T11670]  ? lockdep_hardirqs_on_prepare+0x43c/0x780
> [   61.864230][T11670]  ? __fget_files+0x3ea/0x460
> [   61.864955][T11670]  ? seqcount_lockdep_reader_access+0x157/0x220
> [   61.866571][T11670]  ? __fdget_pos+0x19e/0x320
> [   61.867414][T11670]  ksys_write+0x19f/0x2c0
> [   61.868263][T11670]  ? __ia32_sys_read+0x90/0x90
> [   61.868996][T11670]  ? ktime_get_coarse_real_ts64+0x10b/0x120
> [   61.869896][T11670]  do_syscall_64+0xec/0x210
> [   61.870592][T11670]  entry_SYSCALL_64_after_hwframe+0x67/0x6f
> [   61.871595][T11670] RIP: 0033:0x472a4f
> [   61.873158][T11670] Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 c9 d8 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 0c d9 02 00 48
> [   61.876447][T11670] RSP: 002b:00007f7a7a90f5c0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
> [   61.877944][T11670] RAX: ffffffffffffffda RBX: 00007f7a7a911640 RCX: 0000000000472a4f
> [   61.879751][T11670] RDX: 0000000000000066 RSI: 0000000020000440 RDI: 00000000000000c8
> [   61.881100][T11670] RBP: 00007f7a7a90f620 R08: 0000000000000000 R09: 0000000100000000
> [   61.882298][T11670] R10: 0000000100000000 R11: 0000000000000293 R12: 00007f7a7a911640
> [   61.883501][T11670] R13: 000000000000006e R14: 000000000042f2f0 R15: 00007f7a7a8f1000
> [   61.885999][T11670]  </TASK>
>
> Signed-off-by: Radoslaw Zielonek <[email-masked]>
> ---
>  kernel/bpf/cpumap.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index a8e34416e960..0034a6d423b6 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -59,6 +59,9 @@ struct bpf_cpu_map_entry {
>  	u32 cpu;    /* kthread CPU and map index */
>  	int map_id; /* Back reference to map */
>  
> +	/* Used to end ownership transfer transaction */
> +	struct bpf_map *parent_map;
> +
>  	/* XDP can run multiple RX-ring queues, need __percpu enqueue store */
>  	struct xdp_bulk_queue __percpu *bulkq;
>  
> @@ -427,6 +430,7 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
>  	rcpu->cpu    = cpu;
>  	rcpu->map_id = map->id;
>  	rcpu->value.qsize  = value->qsize;
> +	rcpu->parent_map = map;
>  
>  	if (fd > 0 && __cpu_map_load_bpf_program(rcpu, map, fd))
>  		goto free_ptr_ring;
> @@ -639,6 +643,14 @@ static int cpu_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>  
>  static long cpu_map_redirect(struct bpf_map *map, u64 index, u64 flags)
>  {
> +	/*
> +	 * Redirection is a transfer of ownership of the bpf_cpu_map_entry
> +	 * During the transfer the bpf_cpu_map_entry is still in the map,
> +	 * so we need to prevent it from being freed.
> +	 * The bpf_map_inc() increments the refcnt of the map, so the
> +	 * bpf_cpu_map_entry will not be freed until the refcnt is decremented.
> +	 */
> +	bpf_map_inc(map);

Adding refcnt increase/decrease in the fast path? Hard NAK.

The map entry is protected by RCU, which should prevent this kind of UAF
from happening. Looks like maybe there's a bug in the tun driver so this
RCU protection is not working?

-Toke