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authorDaniel Borkmann <daniel@iogearbox.net>2018-01-18 01:15:21 +0100
committerAlexei Starovoitov <ast@kernel.org>2018-01-17 16:23:17 -0800
commit6f16101e6a8b4324c36e58a29d9e0dbb287cdedb (patch)
tree71777cf318b1d7701d9b014aca031117a8fe42a3 /kernel
parentf37a8cb84cce18762e8f86a70bd6a49a66ab964c (diff)
bpf: mark dst unknown on inconsistent {s, u}bounds adjustments
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 <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c27
1 files changed, 16 insertions, 11 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index eb062b0fbf27..13551e623501 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1895,17 +1895,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
dst_reg = &regs[dst];
- if (WARN_ON_ONCE(known && (smin_val != smax_val))) {
- print_verifier_state(env, env->cur_state);
- verbose(env,
- "verifier internal error: known but bad sbounds\n");
- return -EINVAL;
- }
- if (WARN_ON_ONCE(known && (umin_val != umax_val))) {
- print_verifier_state(env, env->cur_state);
- verbose(env,
- "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) {
@@ -2097,6 +2093,15 @@ 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);