From ddf0936b9eefe0af6d046cd7d6a9212478812c9a Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 18 Jan 2018 01:15:21 +0100 Subject: bpf: mark dst unknown on inconsistent {s, u}bounds adjustments commit 6f16101e6a8b4324c36e58a29d9e0dbb287cdedb upstream. syzkaller generated a BPF proglet and triggered a warning with the following: 0: (b7) r0 = 0 1: (d5) if r0 s<= 0x0 goto pc+0 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 2: (1f) r0 -= r1 R0=inv0 R1=ctx(id=0,off=0,imm=0) R10=fp0 verifier internal error: known but bad sbounds What happens is that in the first insn, r0's min/max value are both 0 due to the immediate assignment, later in the jsle test the bounds are updated for the min value in the false path, meaning, they yield smin_val = 1, smax_val = 0, and when ctx pointer is subtracted from r0, verifier bails out with the internal error and throwing a WARN since smin_val != smax_val for the known constant. For min_val > max_val scenario it means that reg_set_min_max() and reg_set_min_max_inv() (which both refine existing bounds) demonstrated that such branch cannot be taken at runtime. In above scenario for the case where it will be taken, the existing [0, 0] bounds are kept intact. Meaning, the rejection is not due to a verifier internal error, and therefore the WARN() is not necessary either. We could just reject such cases in adjust_{ptr,scalar}_min_max_vals() when either known scalars have smin_val != smax_val or umin_val != umax_val or any scalar reg with bounds smin_val > smax_val or umin_val > umax_val. However, there may be a small risk of breakage of buggy programs, so handle this more gracefully and in adjust_{ptr,scalar}_min_max_vals() just taint the dst reg as unknown scalar when we see ops with such kind of src reg. Reported-by: syzbot+6d362cadd45dc0a12ba4@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) (limited to 'kernel/bpf') diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f9339c3219bc..b5ae6488b890 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1865,15 +1865,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, dst_reg = ®s[dst]; - if (WARN_ON_ONCE(known && (smin_val != smax_val))) { - print_verifier_state(&env->cur_state); - verbose("verifier internal error: known but bad sbounds\n"); - return -EINVAL; - } - if (WARN_ON_ONCE(known && (umin_val != umax_val))) { - print_verifier_state(&env->cur_state); - verbose("verifier internal error: known but bad ubounds\n"); - return -EINVAL; + if ((known && (smin_val != smax_val || umin_val != umax_val)) || + smin_val > smax_val || umin_val > umax_val) { + /* Taint dst register if offset had invalid bounds derived from + * e.g. dead branches. + */ + __mark_reg_unknown(dst_reg); + return 0; } if (BPF_CLASS(insn->code) != BPF_ALU64) { @@ -2075,6 +2073,15 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, src_known = tnum_is_const(src_reg.var_off); dst_known = tnum_is_const(dst_reg->var_off); + if ((src_known && (smin_val != smax_val || umin_val != umax_val)) || + smin_val > smax_val || umin_val > umax_val) { + /* Taint dst register if offset had invalid bounds derived from + * e.g. dead branches. + */ + __mark_reg_unknown(dst_reg); + return 0; + } + if (!src_known && opcode != BPF_ADD && opcode != BPF_SUB && opcode != BPF_AND) { __mark_reg_unknown(dst_reg); -- cgit v1.2.3