Radoslaw Zielonek <radoslaw.zielonek@xxxxxxxxx> 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 <radoslaw.zielonek@xxxxxxxxx>
> ---
> 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
