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bpf: disallow direct packet access for unpriv in cg_skb 

Commit b39b5f411d ("bpf: add cg_skb_is_valid_access for
BPF_PROG_TYPE_CGROUP_SKB") added support for returning pkt pointers
for direct packet access. Given this program type is allowed for both
unprivileged and privileged users, we shouldn't allow unprivileged
ones to use it, e.g. besides others one reason would be to avoid any
potential speculation on the packet test itself, thus guard this for
root only.

Fixes: b39b5f411d ("bpf: add cg_skb_is_valid_access for BPF_PROG_TYPE_CGROUP_SKB")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2018-10-24 22:05:44 +02:00 committed by Alexei Starovoitov
parent 36641ad61d
commit ab21c1b5f7
2 changed files with 7 additions and 1 deletions
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6
net/core/filter.c
View File

@ -5496,7 +5496,13 @@ static bool cg_skb_is_valid_access(int off, int size,
case bpf_ctx_range(struct __sk_buff, data_meta):
case bpf_ctx_range(struct __sk_buff, flow_keys):
return false;
case bpf_ctx_range(struct __sk_buff, data):
case bpf_ctx_range(struct __sk_buff, data_end):
if (!capable(CAP_SYS_ADMIN))
return false;
break;
}
if (type == BPF_WRITE) {
switch (off) {
case bpf_ctx_range(struct __sk_buff, mark):

2
tools/testing/selftests/bpf/test_verifier.c
View File

@ -4892,7 +4892,7 @@ static struct bpf_test tests[] = {
},
.result = ACCEPT,
.result_unpriv = REJECT,
.errstr_unpriv = "R3 pointer comparison prohibited",
.errstr_unpriv = "invalid bpf_context access off=76 size=4",
.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
},
{