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authorJann Horn <jannh@google.com>2017-12-01 01:46:07 +0100
committerPablo Neira Ayuso <pablo@netfilter.org>2017-12-04 11:41:20 +0100
commit6ab405114b0b229151ef06f4e31c7834dd09d0c0 (patch)
tree275a572b5dff2fd38cf14fa965868ad88fd4b491 /net/netfilter
parent4b380c42f7d00a395feede754f0bc2292eebe6e5 (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/netfilter')
-rw-r--r--net/netfilter/xt_bpf.c6
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);