3.16.55-rc1 review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit 6ab405114b0b229151ef06f4e31c7834dd09d0c0 upstream.
Check whether inputs from userspace are too long (explicit length field too big or string not null-terminated) to avoid out-of-bounds reads.
As far as I can tell, this can at worst lead to very limited kernel heap memory disclosure or oopses.
This bug can be triggered by an unprivileged user even if the xt_bpf module is not loaded: iptables is available in network namespaces, and the xt_bpf module can be autoloaded.
Triggering the bug with a classic BPF filter with fake length 0x1000 causes the following KASAN report:
================================================================== BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 Read of size 32768 at addr ffff8801eff2c494 by task test/4627
CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 [...] Call Trace: dump_stack+0x5c/0x85 print_address_description+0x6a/0x260 kasan_report+0x254/0x370 ? bpf_prog_create+0x84/0xf0 memcpy+0x1f/0x50 bpf_prog_create+0x84/0xf0 bpf_mt_check+0x90/0xd6 [xt_bpf] [...] Allocated by task 4627: kasan_kmalloc+0xa0/0xd0 __kmalloc_node+0x47/0x60 xt_alloc_table_info+0x41/0x70 [x_tables] [...] The buggy address belongs to the object at ffff8801eff2c3c0 which belongs to the cache kmalloc-2048 of size 2048 The buggy address is located 212 bytes inside of 2048-byte region [ffff8801eff2c3c0, ffff8801eff2cbc0) [...] ==================================================================
Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org [bwh: Backported to 3.16: - Add len variable in bpf_mt_check() - Drop change in __bpf_mt_check_path()] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/net/netfilter/xt_bpf.c +++ b/net/netfilter/xt_bpf.c @@ -24,8 +24,12 @@ static int bpf_mt_check(const struct xt_ { struct xt_bpf_info *info = par->matchinfo; struct sock_fprog_kern program; + u16 len = info->bpf_program_num_elem;
- program.len = info->bpf_program_num_elem; + if (len > XT_BPF_MAX_NUM_INSTR) + return -EINVAL; + + program.len = len; program.filter = info->bpf_program;
if (sk_unattached_filter_create(&info->filter, &program)) {