From: Tatsuhiko Yasumatsu th.yasumatsu@gmail.com
[ Upstream commit c4eb1f403243fc7bbb7de644db8587c03de36da6 ]
In __htab_map_lookup_and_delete_batch(), hash buckets are iterated over to count the number of elements in each bucket (bucket_size). If bucket_size is large enough, the multiplication to calculate kvmalloc() size could overflow, resulting in out-of-bounds write as reported by KASAN:
[...] [ 104.986052] BUG: KASAN: vmalloc-out-of-bounds in __htab_map_lookup_and_delete_batch+0x5ce/0xb60 [ 104.986489] Write of size 4194224 at addr ffffc9010503be70 by task crash/112 [ 104.986889] [ 104.987193] CPU: 0 PID: 112 Comm: crash Not tainted 5.14.0-rc4 #13 [ 104.987552] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 [ 104.988104] Call Trace: [ 104.988410] dump_stack_lvl+0x34/0x44 [ 104.988706] print_address_description.constprop.0+0x21/0x140 [ 104.988991] ? __htab_map_lookup_and_delete_batch+0x5ce/0xb60 [ 104.989327] ? __htab_map_lookup_and_delete_batch+0x5ce/0xb60 [ 104.989622] kasan_report.cold+0x7f/0x11b [ 104.989881] ? __htab_map_lookup_and_delete_batch+0x5ce/0xb60 [ 104.990239] kasan_check_range+0x17c/0x1e0 [ 104.990467] memcpy+0x39/0x60 [ 104.990670] __htab_map_lookup_and_delete_batch+0x5ce/0xb60 [ 104.990982] ? __wake_up_common+0x4d/0x230 [ 104.991256] ? htab_of_map_free+0x130/0x130 [ 104.991541] bpf_map_do_batch+0x1fb/0x220 [...]
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 trigger the integer overflow.
Triggering the overflow is possible for both callers with CAP_SYS_ADMIN and callers without CAP_SYS_ADMIN.
It will be trivial for a caller with CAP_SYS_ADMIN to intentionally reach this overflow by enabling BPF_F_ZERO_SEED. As this flag will set the random seed passed to jhash() to 0, it will be easy for the caller to prepare keys which will be hashed into the same value, and thus put all the elements into the same bucket.
If the caller does not have CAP_SYS_ADMIN, BPF_F_ZERO_SEED cannot be used. However, it will be still technically possible to trigger the overflow, by guessing the random seed value passed to jhash() (32bit) and repeating the attempt to trigger the overflow. In this case, the probability to trigger the overflow will be low and will take a very long time.
Fix the integer overflow by calling kvmalloc_array() instead of kvmalloc() to allocate memory.
Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map") Signed-off-by: Tatsuhiko Yasumatsu th.yasumatsu@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20210806150419.109658-1-th.yasumatsu@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/hashtab.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index d7ebb12ffffc..49857e8cd6ce 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -1464,8 +1464,8 @@ alloc: /* We cannot do copy_from_user or copy_to_user inside * the rcu_read_lock. Allocate enough space here. */ - keys = kvmalloc(key_size * bucket_size, GFP_USER | __GFP_NOWARN); - values = kvmalloc(value_size * bucket_size, GFP_USER | __GFP_NOWARN); + keys = kvmalloc_array(key_size, bucket_size, GFP_USER | __GFP_NOWARN); + values = kvmalloc_array(value_size, bucket_size, GFP_USER | __GFP_NOWARN); if (!keys || !values) { ret = -ENOMEM; goto after_loop;