bpf: Ensure off_reg has no mixed signed bounds for all types

commit 24c109bb1537c12c02aeed2d51a347b4d6a9b76e upstream.

The mixed signed bounds check really belongs into retrieve_ptr_limit()
instead of outside of it in adjust_ptr_min_max_vals(). The reason is
that this check is not tied to PTR_TO_MAP_VALUE only, but to all pointer
types that we handle in retrieve_ptr_limit() and given errors from the latter
propagate back to adjust_ptr_min_max_vals() and lead to rejection of the
program, it's a better place to reside to avoid anything slipping through
for future types. The reason why we must reject such off_reg is that we
otherwise would not be able to derive a mask, see details in 9d7eceede769
("bpf: restrict unknown scalars of mixed signed bounds for unprivileged").

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
[fllinden@amazon.com: backport to 5.4]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[OP: backport to 4.19]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4edae9b..cdef8c7 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2730,12 +2730,18 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env)
 }
 
 static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
-                             u32 *ptr_limit, u8 opcode, bool off_is_neg)
+                             const struct bpf_reg_state *off_reg,
+                             u32 *ptr_limit, u8 opcode)
 {
+       bool off_is_neg = off_reg->smin_value < 0;
        bool mask_to_left = (opcode == BPF_ADD &&  off_is_neg) ||
                            (opcode == BPF_SUB && !off_is_neg);
        u32 off, max;
 
+       if (!tnum_is_const(off_reg->var_off) &&
+           (off_reg->smin_value < 0) != (off_reg->smax_value < 0))
+               return -EACCES;
+
        switch (ptr_reg->type) {
        case PTR_TO_STACK:
                /* Offset 0 is out-of-bounds, but acceptable start for the
@@ -2826,7 +2832,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
        alu_state |= ptr_is_dst_reg ?
                     BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;
 
-       err = retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg);
+       err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode);
        if (err < 0)
                return err;
 
@@ -2871,8 +2877,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
            smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value;
        u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value,
            umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value;
-       u32 dst = insn->dst_reg, src = insn->src_reg;
        u8 opcode = BPF_OP(insn->code);
+       u32 dst = insn->dst_reg;
        int ret;
 
        dst_reg = &regs[dst];
@@ -2909,12 +2915,6 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
                        dst);
                return -EACCES;
        }
-       if (ptr_reg->type == PTR_TO_MAP_VALUE &&
-           !env->allow_ptr_leaks && !known && (smin_val < 0) != (smax_val < 0)) {
-               verbose(env, "R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n",
-                       off_reg == dst_reg ? dst : src);
-               return -EACCES;
-       }
 
        /* In case of 'scalar += pointer', dst_reg inherits pointer type and id.
         * The id may be overwritten later if we create a new variable offset.