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author | Daniel Borkmann <daniel@iogearbox.net> | 2017-06-29 03:04:59 +0200 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2017-06-29 15:44:34 -0400 |
commit | 6bdf6abc56b53103324dfd270a86580306e1a232 (patch) | |
tree | 2ab300507010ec4dc0895936ae04718984823086 /tools/testing/selftests | |
parent | 00778f7cadd393630a23e83ffaf60b70fe460879 (diff) | |
download | op-kernel-dev-6bdf6abc56b53103324dfd270a86580306e1a232.zip op-kernel-dev-6bdf6abc56b53103324dfd270a86580306e1a232.tar.gz |
bpf: prevent leaking pointer via xadd on unpriviledged
Leaking kernel addresses on unpriviledged is generally disallowed,
for example, verifier rejects the following:
0: (b7) r0 = 0
1: (18) r2 = 0xffff897e82304400
3: (7b) *(u64 *)(r1 +48) = r2
R2 leaks addr into ctx
Doing pointer arithmetic on them is also forbidden, so that they
don't turn into unknown value and then get leaked out. However,
there's xadd as a special case, where we don't check the src reg
for being a pointer register, e.g. the following will pass:
0: (b7) r0 = 0
1: (7b) *(u64 *)(r1 +48) = r0
2: (18) r2 = 0xffff897e82304400 ; map
4: (db) lock *(u64 *)(r1 +48) += r2
5: (95) exit
We could store the pointer into skb->cb, loose the type context,
and then read it out from there again to leak it eventually out
of a map value. Or more easily in a different variant, too:
0: (bf) r6 = r1
1: (7a) *(u64 *)(r10 -8) = 0
2: (bf) r2 = r10
3: (07) r2 += -8
4: (18) r1 = 0x0
6: (85) call bpf_map_lookup_elem#1
7: (15) if r0 == 0x0 goto pc+3
R0=map_value(ks=8,vs=8,id=0),min_value=0,max_value=0 R6=ctx R10=fp
8: (b7) r3 = 0
9: (7b) *(u64 *)(r0 +0) = r3
10: (db) lock *(u64 *)(r0 +0) += r6
11: (b7) r0 = 0
12: (95) exit
from 7 to 11: R0=inv,min_value=0,max_value=0 R6=ctx R10=fp
11: (b7) r0 = 0
12: (95) exit
Prevent this by checking xadd src reg for pointer types. Also
add a couple of test cases related to this.
Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs")
Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'tools/testing/selftests')
-rw-r--r-- | tools/testing/selftests/bpf/test_verifier.c | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index cabb19b..0ff8c55 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -3749,6 +3749,72 @@ static struct bpf_test tests[] = { .errstr = "invalid bpf_context access", }, { + "leak pointer into ctx 1", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, + offsetof(struct __sk_buff, cb[0])), + BPF_LD_MAP_FD(BPF_REG_2, 0), + BPF_STX_XADD(BPF_DW, BPF_REG_1, BPF_REG_2, + offsetof(struct __sk_buff, cb[0])), + BPF_EXIT_INSN(), + }, + .fixup_map1 = { 2 }, + .errstr_unpriv = "R2 leaks addr into mem", + .result_unpriv = REJECT, + .result = ACCEPT, + }, + { + "leak pointer into ctx 2", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, + offsetof(struct __sk_buff, cb[0])), + BPF_STX_XADD(BPF_DW, BPF_REG_1, BPF_REG_10, + offsetof(struct __sk_buff, cb[0])), + BPF_EXIT_INSN(), + }, + .errstr_unpriv = "R10 leaks addr into mem", + .result_unpriv = REJECT, + .result = ACCEPT, + }, + { + "leak pointer into ctx 3", + .insns = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_LD_MAP_FD(BPF_REG_2, 0), + BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_2, + offsetof(struct __sk_buff, cb[0])), + BPF_EXIT_INSN(), + }, + .fixup_map1 = { 1 }, + .errstr_unpriv = "R2 leaks addr into ctx", + .result_unpriv = REJECT, + .result = ACCEPT, + }, + { + "leak pointer into map val", + .insns = { + BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), + BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), + BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_LD_MAP_FD(BPF_REG_1, 0), + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, + BPF_FUNC_map_lookup_elem), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3), + BPF_MOV64_IMM(BPF_REG_3, 0), + BPF_STX_MEM(BPF_DW, BPF_REG_0, BPF_REG_3, 0), + BPF_STX_XADD(BPF_DW, BPF_REG_0, BPF_REG_6, 0), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .fixup_map1 = { 4 }, + .errstr_unpriv = "R6 leaks addr into mem", + .result_unpriv = REJECT, + .result = ACCEPT, + }, + { "helper access to map: full range", .insns = { BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), |