diff options
| author | Jann Horn <jannh@google.com> | 2017-12-01 01:46:07 +0100 |
|---|---|---|
| committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2017-12-04 11:41:20 +0100 |
| commit | 6ab405114b0b229151ef06f4e31c7834dd09d0c0 (patch) | |
| tree | 275a572b5dff2fd38cf14fa965868ad88fd4b491 /net | |
| parent | 4b380c42f7d00a395feede754f0bc2292eebe6e5 (diff) | |
netfilter: xt_bpf: add overflow checks
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>
Diffstat (limited to 'net')
| -rw-r--r-- | net/netfilter/xt_bpf.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c index 041da0d9c06f..1f7fbd3c7e5a 100644 --- a/net/netfilter/xt_bpf.c +++ b/net/netfilter/xt_bpf.c @@ -27,6 +27,9 @@ static int __bpf_mt_check_bytecode(struct sock_filter *insns, __u16 len, { struct sock_fprog_kern program; + if (len > XT_BPF_MAX_NUM_INSTR) + return -EINVAL; + program.len = len; program.filter = insns; @@ -55,6 +58,9 @@ static int __bpf_mt_check_path(const char *path, struct bpf_prog **ret) mm_segment_t oldfs = get_fs(); int retval, fd; + if (strnlen(path, XT_BPF_PATH_MAX) == XT_BPF_PATH_MAX) + return -EINVAL; + set_fs(KERNEL_DS); fd = bpf_obj_get_user(path, 0); set_fs(oldfs); |