From: Jann Horn jannh@google.com

[ Upstream commit 6ab405114b0b229151ef06f4e31c7834dd09d0c0 ]

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 Signed-off-by: Zubin Mithra zsm@chromium.org --- * Syzkaller triggered an OOB read with the following stacktrace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0xcb/0x130 lib/dump_stack.c:56 print_trailer+0x151/0x15a mm/slub.c:658 object_err+0x35/0x3d mm/slub.c:665 print_address_description mm/kasan/report.c:188 [inline] kasan_report_error mm/kasan/report.c:285 [inline] kasan_report.part.0.cold+0x21a/0x4c1 mm/kasan/report.c:310 kasan_report+0x25/0x30 mm/kasan/report.c:297 check_memory_region_inline mm/kasan/kasan.c:292 [inline] check_memory_region+0x116/0x190 mm/kasan/kasan.c:299 memcpy+0x24/0x50 mm/kasan/kasan.c:334 bpf_prog_create+0xdd/0x230 net/core/filter.c:1075 bpf_mt_check+0xb1/0x100 net/netfilter/xt_bpf.c:31 xt_check_match+0x26b/0x560 net/netfilter/x_tables.c:444 check_match net/ipv4/netfilter/ip_tables.c:593 [inline] find_check_match net/ipv4/netfilter/ip_tables.c:616 [inline] find_check_entry.isra.0+0x2fe/0x950 net/ipv4/netfilter/ip_tables.c:673 translate_table+0xb3f/0x15b0 net/ipv4/netfilter/ip_tables.c:878 do_replace net/ipv4/netfilter/ip_tables.c:1300 [inline] do_ipt_set_ctl+0x2cf/0x460 net/ipv4/netfilter/ip_tables.c:1864 nf_sockopt net/netfilter/nf_sockopt.c:105 [inline] nf_setsockopt+0x72/0xd0 net/netfilter/nf_sockopt.c:114 ip_setsockopt net/ipv4/ip_sockglue.c:1227 [inline] ip_setsockopt+0xa0/0xb0 net/ipv4/ip_sockglue.c:1212 udp_setsockopt+0x53/0x90 net/ipv4/udp.c:2162 sock_common_setsockopt+0x9f/0xe0 net/core/sock.c:2697 SYSC_setsockopt net/socket.c:1769 [inline] SyS_setsockopt+0x146/0x210 net/socket.c:1748 entry_SYSCALL_64_fastpath+0x1e/0xa0

* This commit is present in linux-4.14.y.

* This patch resolves conflicts that arise due to the following commit not being present in linux-4.9.y, linux-4.4.y: - 2c16d6033264 ("netfilter: xt_bpf: support ebpf")

* Tests run: syzkaller reproducer

net/netfilter/xt_bpf.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c index dffee9d47ec4b..7b993f25aab92 100644 --- a/net/netfilter/xt_bpf.c +++ b/net/netfilter/xt_bpf.c @@ -25,6 +25,9 @@ static int bpf_mt_check(const struct xt_mtchk_param *par) struct xt_bpf_info *info = par->matchinfo; struct sock_fprog_kern program;

+ if (info->bpf_program_num_elem > XT_BPF_MAX_NUM_INSTR) + return -EINVAL; + program.len = info->bpf_program_num_elem; program.filter = info->bpf_program;