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bpf: Add PTR_TO_SOCKET verifier type
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Teach the verifier a little bit about a new type of pointer, a
PTR_TO_SOCKET. This pointer type is accessed from BPF through the
'struct bpf_sock' structure.

Signed-off-by: Joe Stringer <joe@wand.net.nz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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Joe Stringer authored and Daniel Borkmann committed Oct 3, 2018
1 parent 840b961 commit c64b798
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Showing 4 changed files with 160 additions and 26 deletions.
34 changes: 34 additions & 0 deletions include/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,7 @@ enum bpf_arg_type {

ARG_PTR_TO_CTX, /* pointer to context */
ARG_ANYTHING, /* any (initialized) argument is ok */
ARG_PTR_TO_SOCKET, /* pointer to bpf_sock */
};

/* type of values returned from helper functions */
Expand All @@ -162,6 +163,7 @@ enum bpf_return_type {
RET_VOID, /* function doesn't return anything */
RET_PTR_TO_MAP_VALUE, /* returns a pointer to map elem value */
RET_PTR_TO_MAP_VALUE_OR_NULL, /* returns a pointer to map elem value or NULL */
RET_PTR_TO_SOCKET_OR_NULL, /* returns a pointer to a socket or NULL */
};

/* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
Expand Down Expand Up @@ -213,6 +215,8 @@ enum bpf_reg_type {
PTR_TO_PACKET, /* reg points to skb->data */
PTR_TO_PACKET_END, /* skb->data + headlen */
PTR_TO_FLOW_KEYS, /* reg points to bpf_flow_keys */
PTR_TO_SOCKET, /* reg points to struct bpf_sock */
PTR_TO_SOCKET_OR_NULL, /* reg points to struct bpf_sock or NULL */
};

/* The information passed from prog-specific *_is_valid_access
Expand Down Expand Up @@ -343,6 +347,11 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void);

typedef unsigned long (*bpf_ctx_copy_t)(void *dst, const void *src,
unsigned long off, unsigned long len);
typedef u32 (*bpf_convert_ctx_access_t)(enum bpf_access_type type,
const struct bpf_insn *src,
struct bpf_insn *dst,
struct bpf_prog *prog,
u32 *target_size);

u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy);
Expand Down Expand Up @@ -836,4 +845,29 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
void bpf_user_rnd_init_once(void);
u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);

#if defined(CONFIG_NET)
bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,
struct bpf_insn_access_aux *info);
u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
struct bpf_prog *prog,
u32 *target_size);
#else
static inline bool bpf_sock_is_valid_access(int off, int size,
enum bpf_access_type type,
struct bpf_insn_access_aux *info)
{
return false;
}
static inline u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
struct bpf_prog *prog,
u32 *target_size)
{
return 0;
}
#endif

#endif /* _LINUX_BPF_H */
2 changes: 2 additions & 0 deletions include/linux/bpf_verifier.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,8 @@ struct bpf_reg_state {
* offset, so they can share range knowledge.
* For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
* came from, when one is tested for != NULL.
* For PTR_TO_SOCKET this is used to share which pointers retain the
* same reference to the socket, to determine proper reference freeing.
*/
u32 id;
/* For scalar types (SCALAR_VALUE), this represents our knowledge of
Expand Down
120 changes: 106 additions & 14 deletions kernel/bpf/verifier.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -80,8 +80,8 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
* (like pointer plus pointer becomes SCALAR_VALUE type)
*
* When verifier sees load or store instructions the type of base register
* can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, PTR_TO_STACK. These are three pointer
* types recognized by check_mem_access() function.
* can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, PTR_TO_STACK, PTR_TO_SOCKET. These are
* four pointer types recognized by check_mem_access() function.
*
* PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
* and the range of [ptr, ptr + map's value_size) is accessible.
Expand Down Expand Up @@ -267,6 +267,8 @@ static const char * const reg_type_str[] = {
[PTR_TO_PACKET_META] = "pkt_meta",
[PTR_TO_PACKET_END] = "pkt_end",
[PTR_TO_FLOW_KEYS] = "flow_keys",
[PTR_TO_SOCKET] = "sock",
[PTR_TO_SOCKET_OR_NULL] = "sock_or_null",
};

static char slot_type_char[] = {
Expand Down Expand Up @@ -973,6 +975,8 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case PTR_TO_PACKET_END:
case PTR_TO_FLOW_KEYS:
case CONST_PTR_TO_MAP:
case PTR_TO_SOCKET:
case PTR_TO_SOCKET_OR_NULL:
return true;
default:
return false;
Expand Down Expand Up @@ -1341,6 +1345,28 @@ static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
return 0;
}

static int check_sock_access(struct bpf_verifier_env *env, u32 regno, int off,
int size, enum bpf_access_type t)
{
struct bpf_reg_state *regs = cur_regs(env);
struct bpf_reg_state *reg = &regs[regno];
struct bpf_insn_access_aux info;

if (reg->smin_value < 0) {
verbose(env, "R%d min value is negative, either use unsigned index or do a if (index >=0) check.\n",
regno);
return -EACCES;
}

if (!bpf_sock_is_valid_access(off, size, t, &info)) {
verbose(env, "invalid bpf_sock access off=%d size=%d\n",
off, size);
return -EACCES;
}

return 0;
}

static bool __is_pointer_value(bool allow_ptr_leaks,
const struct bpf_reg_state *reg)
{
Expand Down Expand Up @@ -1459,6 +1485,9 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
*/
strict = true;
break;
case PTR_TO_SOCKET:
pointer_desc = "sock ";
break;
default:
break;
}
Expand Down Expand Up @@ -1726,6 +1755,14 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
err = check_flow_keys_access(env, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown(env, regs, value_regno);
} else if (reg->type == PTR_TO_SOCKET) {
if (t == BPF_WRITE) {
verbose(env, "cannot write into socket\n");
return -EACCES;
}
err = check_sock_access(env, regno, off, size, t);
if (!err && value_regno >= 0)
mark_reg_unknown(env, regs, value_regno);
} else {
verbose(env, "R%d invalid mem access '%s'\n", regno,
reg_type_str[reg->type]);
Expand Down Expand Up @@ -1948,6 +1985,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
err = check_ctx_reg(env, reg, regno);
if (err < 0)
return err;
} else if (arg_type == ARG_PTR_TO_SOCKET) {
expected_type = PTR_TO_SOCKET;
if (type != expected_type)
goto err_type;
} else if (arg_type_is_mem_ptr(arg_type)) {
expected_type = PTR_TO_STACK;
/* One exception here. In case function allows for NULL to be
Expand Down Expand Up @@ -2543,6 +2584,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
}
regs[BPF_REG_0].map_ptr = meta.map_ptr;
regs[BPF_REG_0].id = ++env->id_gen;
} else if (fn->ret_type == RET_PTR_TO_SOCKET_OR_NULL) {
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].type = PTR_TO_SOCKET_OR_NULL;
regs[BPF_REG_0].id = ++env->id_gen;
} else {
verbose(env, "unknown return type %d of func %s#%d\n",
fn->ret_type, func_id_name(func_id), func_id);
Expand Down Expand Up @@ -2680,6 +2725,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
return -EACCES;
case CONST_PTR_TO_MAP:
case PTR_TO_PACKET_END:
case PTR_TO_SOCKET:
case PTR_TO_SOCKET_OR_NULL:
verbose(env, "R%d pointer arithmetic on %s prohibited\n",
dst, reg_type_str[ptr_reg->type]);
return -EACCES;
Expand Down Expand Up @@ -3627,6 +3674,8 @@ static void mark_ptr_or_null_reg(struct bpf_reg_state *reg, u32 id,
} else {
reg->type = PTR_TO_MAP_VALUE;
}
} else if (reg->type == PTR_TO_SOCKET_OR_NULL) {
reg->type = PTR_TO_SOCKET;
}
/* We don't need id from this point onwards anymore, thus we
* should better reset it, so that state pruning has chances
Expand Down Expand Up @@ -4402,6 +4451,8 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
case CONST_PTR_TO_MAP:
case PTR_TO_PACKET_END:
case PTR_TO_FLOW_KEYS:
case PTR_TO_SOCKET:
case PTR_TO_SOCKET_OR_NULL:
/* Only valid matches are exact, which memcmp() above
* would have accepted
*/
Expand Down Expand Up @@ -4679,6 +4730,37 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
return 0;
}

/* Return true if it's OK to have the same insn return a different type. */
static bool reg_type_mismatch_ok(enum bpf_reg_type type)
{
switch (type) {
case PTR_TO_CTX:
case PTR_TO_SOCKET:
case PTR_TO_SOCKET_OR_NULL:
return false;
default:
return true;
}
}

/* If an instruction was previously used with particular pointer types, then we
* need to be careful to avoid cases such as the below, where it may be ok
* for one branch accessing the pointer, but not ok for the other branch:
*
* R1 = sock_ptr
* goto X;
* ...
* R1 = some_other_valid_ptr;
* goto X;
* ...
* R2 = *(u32 *)(R1 + 0);
*/
static bool reg_type_mismatch(enum bpf_reg_type src, enum bpf_reg_type prev)
{
return src != prev && (!reg_type_mismatch_ok(src) ||
!reg_type_mismatch_ok(prev));
}

static int do_check(struct bpf_verifier_env *env)
{
struct bpf_verifier_state *state;
Expand Down Expand Up @@ -4811,9 +4893,7 @@ static int do_check(struct bpf_verifier_env *env)
*/
*prev_src_type = src_reg_type;

} else if (src_reg_type != *prev_src_type &&
(src_reg_type == PTR_TO_CTX ||
*prev_src_type == PTR_TO_CTX)) {
} else if (reg_type_mismatch(src_reg_type, *prev_src_type)) {
/* ABuser program is trying to use the same insn
* dst_reg = *(u32*) (src_reg + off)
* with different pointer types:
Expand Down Expand Up @@ -4858,9 +4938,7 @@ static int do_check(struct bpf_verifier_env *env)

if (*prev_dst_type == NOT_INIT) {
*prev_dst_type = dst_reg_type;
} else if (dst_reg_type != *prev_dst_type &&
(dst_reg_type == PTR_TO_CTX ||
*prev_dst_type == PTR_TO_CTX)) {
} else if (reg_type_mismatch(dst_reg_type, *prev_dst_type)) {
verbose(env, "same insn cannot be used with different pointers\n");
return -EINVAL;
}
Expand Down Expand Up @@ -5286,8 +5364,10 @@ static void sanitize_dead_code(struct bpf_verifier_env *env)
}
}

/* convert load instructions that access fields of 'struct __sk_buff'
* into sequence of instructions that access fields of 'struct sk_buff'
/* convert load instructions that access fields of a context type into a
* sequence of instructions that access fields of the underlying structure:
* struct __sk_buff -> struct sk_buff
* struct bpf_sock_ops -> struct sock
*/
static int convert_ctx_accesses(struct bpf_verifier_env *env)
{
Expand Down Expand Up @@ -5316,12 +5396,14 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
}
}

if (!ops->convert_ctx_access || bpf_prog_is_dev_bound(env->prog->aux))
if (bpf_prog_is_dev_bound(env->prog->aux))
return 0;

insn = env->prog->insnsi + delta;

for (i = 0; i < insn_cnt; i++, insn++) {
bpf_convert_ctx_access_t convert_ctx_access;

if (insn->code == (BPF_LDX | BPF_MEM | BPF_B) ||
insn->code == (BPF_LDX | BPF_MEM | BPF_H) ||
insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
Expand Down Expand Up @@ -5363,8 +5445,18 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
continue;
}

if (env->insn_aux_data[i + delta].ptr_type != PTR_TO_CTX)
switch (env->insn_aux_data[i + delta].ptr_type) {
case PTR_TO_CTX:
if (!ops->convert_ctx_access)
continue;
convert_ctx_access = ops->convert_ctx_access;
break;
case PTR_TO_SOCKET:
convert_ctx_access = bpf_sock_convert_ctx_access;
break;
default:
continue;
}

ctx_field_size = env->insn_aux_data[i + delta].ctx_field_size;
size = BPF_LDST_BYTES(insn);
Expand Down Expand Up @@ -5396,8 +5488,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
}

target_size = 0;
cnt = ops->convert_ctx_access(type, insn, insn_buf, env->prog,
&target_size);
cnt = convert_ctx_access(type, insn, insn_buf, env->prog,
&target_size);
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf) ||
(ctx_field_size && !target_size)) {
verbose(env, "bpf verifier is misconfigured\n");
Expand Down
30 changes: 18 additions & 12 deletions net/core/filter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5394,23 +5394,29 @@ static bool __sock_filter_check_size(int off, int size,
return size == size_default;
}

static bool sock_filter_is_valid_access(int off, int size,
enum bpf_access_type type,
const struct bpf_prog *prog,
struct bpf_insn_access_aux *info)
bool bpf_sock_is_valid_access(int off, int size, enum bpf_access_type type,
struct bpf_insn_access_aux *info)
{
if (off < 0 || off >= sizeof(struct bpf_sock))
return false;
if (off % size != 0)
return false;
if (!__sock_filter_check_attach_type(off, type,
prog->expected_attach_type))
return false;
if (!__sock_filter_check_size(off, size, info))
return false;
return true;
}

static bool sock_filter_is_valid_access(int off, int size,
enum bpf_access_type type,
const struct bpf_prog *prog,
struct bpf_insn_access_aux *info)
{
if (!bpf_sock_is_valid_access(off, size, type, info))
return false;
return __sock_filter_check_attach_type(off, type,
prog->expected_attach_type);
}

static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
const struct bpf_prog *prog, int drop_verdict)
{
Expand Down Expand Up @@ -6122,10 +6128,10 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
return insn - insn_buf;
}

static u32 sock_filter_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
struct bpf_prog *prog, u32 *target_size)
u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
struct bpf_prog *prog, u32 *target_size)
{
struct bpf_insn *insn = insn_buf;
int off;
Expand Down Expand Up @@ -7037,7 +7043,7 @@ const struct bpf_prog_ops lwt_seg6local_prog_ops = {
const struct bpf_verifier_ops cg_sock_verifier_ops = {
.get_func_proto = sock_filter_func_proto,
.is_valid_access = sock_filter_is_valid_access,
.convert_ctx_access = sock_filter_convert_ctx_access,
.convert_ctx_access = bpf_sock_convert_ctx_access,
};

const struct bpf_prog_ops cg_sock_prog_ops = {
Expand Down

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