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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id c136sm6893037pfc.53.2021.08.05.07.26.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Aug 2021 07:26:50 -0700 (PDT) Date: Thu, 5 Aug 2021 07:26:49 -0700 From: Kees Cook To: Tatsuhiko Yasumatsu Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH] bpf: Fix integer overflow involving bucket_size Message-ID: <202108050725.384AA3E0@keescook> References: <20210805140515.35630-1-th.yasumatsu@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210805140515.35630-1-th.yasumatsu@gmail.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Aug 05, 2021 at 11:05:15PM +0900, Tatsuhiko Yasumatsu wrote: > 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 casting 1 operand to u64. > > Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map") > Signed-off-by: Tatsuhiko Yasumatsu > --- > 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 72c58cc516a3..e29283c3b17f 100644 > --- a/kernel/bpf/hashtab.c > +++ b/kernel/bpf/hashtab.c > @@ -1565,8 +1565,8 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map, > /* 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((u64)key_size * bucket_size, GFP_USER | __GFP_NOWARN); > + values = kvmalloc((u64)value_size * bucket_size, GFP_USER | __GFP_NOWARN); Please, no open-coded multiplication[1]. This should use kvmalloc_array() instead. -Kees [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments > if (!keys || !values) { > ret = -ENOMEM; > goto after_loop; > -- > 2.25.1 > -- Kees Cook