[PATCH 5.15 11/71] bpf: Fix ringbuf memory type confusion when passing to helpers

Greg Kroah-Hartman
2024-04-23T21:46:09Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit a672b2e36a648afb04ad3bda93b6bda947a479a5 upstream.

The bpf_ringbuf_submit() and bpf_ringbuf_discard() have ARG_PTR_TO_ALLOC_MEM
in their bpf_func_proto definition as their first argument, and thus both expect
the result from a prior bpf_ringbuf_reserve() call which has a return type of
RET_PTR_TO_ALLOC_MEM_OR_NULL.

While the non-NULL memory from bpf_ringbuf_reserve() can be passed to other
helpers, the two sinks (bpf_ringbuf_submit(), bpf_ringbuf_discard()) right now
only enforce a register type of PTR_TO_MEM.

This can lead to potential type confusion since it would allow other PTR_TO_MEM
memory to be passed into the two sinks which did not come from bpf_ringbuf_reserve().

Add a new MEM_ALLOC composable type attribute for PTR_TO_MEM, and enforce that:

- bpf_ringbuf_reserve() returns NULL or PTR_TO_MEM | MEM_ALLOC
- bpf_ringbuf_submit() and bpf_ringbuf_discard() only take PTR_TO_MEM | MEM_ALLOC
but not plain PTR_TO_MEM arguments via ARG_PTR_TO_ALLOC_MEM
- however, other helpers might treat PTR_TO_MEM | MEM_ALLOC as plain PTR_TO_MEM
to populate the memory area when they use ARG_PTR_TO_{UNINIT_,}MEM in their
func proto description

Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Edward Liaw <edliaw@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/bpf.h | 9 +++++++--
kernel/bpf/verifier.c | 6 +++++-
2 files changed, 12 insertions(+), 3 deletions(-)

--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -321,7 +321,12 @@ enum bpf_type_flag {
*/
MEM_RDONLY = BIT(1 + BPF_BASE_TYPE_BITS),

- __BPF_TYPE_LAST_FLAG = MEM_RDONLY,
+ /* MEM was "allocated" from a different helper, and cannot be mixed
+ * with regular non-MEM_ALLOC'ed MEM types.
+ */
+ MEM_ALLOC = BIT(2 + BPF_BASE_TYPE_BITS),
+
+ __BPF_TYPE_LAST_FLAG = MEM_ALLOC,
};

/* Max number of base types. */
@@ -405,7 +410,7 @@ enum bpf_return_type {
RET_PTR_TO_SOCKET_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_SOCKET,
RET_PTR_TO_TCP_SOCK_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_TCP_SOCK,
RET_PTR_TO_SOCK_COMMON_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_SOCK_COMMON,
- RET_PTR_TO_ALLOC_MEM_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_ALLOC_MEM,
+ RET_PTR_TO_ALLOC_MEM_OR_NULL = PTR_MAYBE_NULL | MEM_ALLOC | RET_PTR_TO_ALLOC_MEM,
RET_PTR_TO_BTF_ID_OR_NULL = PTR_MAYBE_NULL | RET_PTR_TO_BTF_ID,

/* This must be the last entry. Its purpose is to ensure the enum is
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -573,6 +573,8 @@ static const char *reg_type_str(struct b

if (type & MEM_RDONLY)
strncpy(prefix, "rdonly_", 16);
+ if (type & MEM_ALLOC)
+ strncpy(prefix, "alloc_", 16);

snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s%s",
prefix, str[base_type(type)], postfix);
@@ -5157,6 +5159,7 @@ static const struct bpf_reg_types mem_ty
PTR_TO_MAP_KEY,
PTR_TO_MAP_VALUE,
PTR_TO_MEM,
+ PTR_TO_MEM | MEM_ALLOC,
PTR_TO_BUF,
},
};
@@ -5174,7 +5177,7 @@ static const struct bpf_reg_types int_pt
static const struct bpf_reg_types fullsock_types = { .types = { PTR_TO_SOCKET } };
static const struct bpf_reg_types scalar_types = { .types = { SCALAR_VALUE } };
static const struct bpf_reg_types context_types = { .types = { PTR_TO_CTX } };
-static const struct bpf_reg_types alloc_mem_types = { .types = { PTR_TO_MEM } };
+static const struct bpf_reg_types alloc_mem_types = { .types = { PTR_TO_MEM | MEM_ALLOC } };
static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };
static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
@@ -5337,6 +5340,7 @@ static int check_func_arg(struct bpf_ver
case PTR_TO_MAP_VALUE:
case PTR_TO_MEM:
case PTR_TO_MEM | MEM_RDONLY:
+ case PTR_TO_MEM | MEM_ALLOC: