bpf: fix matching of data/data_end in verifier

The ctx structure passed into bpf programs is different depending on bpf
program type. The verifier incorrectly marked ctx->data and ctx->data_end
access based on ctx offset only. That caused loads in tracing programs
int bpf_prog(struct pt_regs *ctx) { .. ctx->ax .. }
to be incorrectly marked as PTR_TO_PACKET which later caused verifier
to reject the program that was actually valid in tracing context.
Fix this by doing program type specific matching of ctx offsets.

Fixes: 969bf05eb3ce ("bpf: direct packet access")
Reported-by: Sasha Goldshtein <goldshtn@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 27 insertions, 1 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8ee27b8afe81..8269cafc6eb1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -111,6 +111,31 @@ enum bpf_access_type {
         BPF_WRITE = 2
 };
 
+/* types of values stored in eBPF registers */
+enum bpf_reg_type {
+        NOT_INIT = 0,            /* nothing was written into register */
+        UNKNOWN_VALUE,           /* reg doesn't contain a valid pointer */
+        PTR_TO_CTX,              /* reg points to bpf_context */
+        CONST_PTR_TO_MAP,        /* reg points to struct bpf_map */
+        PTR_TO_MAP_VALUE,        /* reg points to map element value */
+        PTR_TO_MAP_VALUE_OR_NULL,/* points to map elem value or NULL */
+        FRAME_PTR,               /* reg == frame_pointer */
+        PTR_TO_STACK,            /* reg == frame_pointer + imm */
+        CONST_IMM,               /* constant integer value */
+
+        /* PTR_TO_PACKET represents:
+         * skb->data
+         * skb->data + imm
+         * skb->data + (u16) var
+         * skb->data + (u16) var + imm
+         * if (range > 0) then [ptr, ptr + range - off) is safe to access
+         * if (id > 0) means that some 'var' was added
+         * if (off > 0) menas that 'imm' was added
+         */
+        PTR_TO_PACKET,
+        PTR_TO_PACKET_END,       /* skb->data + headlen */
+};
+
 struct bpf_prog;
 
 struct bpf_verifier_ops {
@@ -120,7 +145,8 @@ struct bpf_verifier_ops {
         /* return true if 'size' wide access at offset 'off' within bpf_context
          * with 'type' (read or write) is allowed
          */
-        bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
+        bool (*is_valid_access)(int off, int size, enum bpf_access_type type,
+                                enum bpf_reg_type *reg_type);
 
         u32 (*convert_ctx_access)(enum bpf_access_type type, int dst_reg,
                                   int src_reg, int ctx_off,