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authorDaniel Borkmann <daniel@iogearbox.net>2016-02-19 23:05:22 +0100
committerDavid S. Miller <davem@davemloft.net>2016-02-21 22:07:09 -0500
commit8e2fe1d9f1a20924f98ea46931a1d7fb092aa876 (patch)
tree538a9916d34e6019f250cc5e4246453786e0848e /kernel/bpf/verifier.c
parent8b393f833346e0a5f0cb4269271d47be8fecd372 (diff)
downloadlinux-sh-8e2fe1d9f1a20924f98ea46931a1d7fb092aa876.tar.gz
bpf: add new arg_type that allows for 0 sized stack buffer
Currently, when we pass a buffer from the eBPF stack into a helper function, the function proto indicates argument types as ARG_PTR_TO_STACK and ARG_CONST_STACK_SIZE pair. If R<X> contains the former, then R<X+1> must be of the latter type. Then, verifier checks whether the buffer points into eBPF stack, is initialized, etc. The verifier also guarantees that the constant value passed in R<X+1> is greater than 0, so helper functions don't need to test for it and can always assume a non-NULL initialized buffer as well as non-0 buffer size. This patch adds a new argument types ARG_CONST_STACK_SIZE_OR_ZERO that allows to also pass NULL as R<X> and 0 as R<X+1> into the helper function. Such helper functions, of course, need to be able to handle these cases internally then. Verifier guarantees that either R<X> == NULL && R<X+1> == 0 or R<X> != NULL && R<X+1> != 0 (like the case of ARG_CONST_STACK_SIZE), any other combinations are not possible to load. I went through various options of extending the verifier, and introducing the type ARG_CONST_STACK_SIZE_OR_ZERO seems to have most minimal changes needed to the verifier. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/bpf/verifier.c')
-rw-r--r--kernel/bpf/verifier.c42
1 files changed, 32 insertions, 10 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 42ba4ccc020b..36dc497deaa3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -779,15 +779,24 @@ static int check_xadd(struct verifier_env *env, struct bpf_insn *insn)
* bytes from that pointer, make sure that it's within stack boundary
* and all elements of stack are initialized
*/
-static int check_stack_boundary(struct verifier_env *env,
- int regno, int access_size)
+static int check_stack_boundary(struct verifier_env *env, int regno,
+ int access_size, bool zero_size_allowed)
{
struct verifier_state *state = &env->cur_state;
struct reg_state *regs = state->regs;
int off, i;
- if (regs[regno].type != PTR_TO_STACK)
+ if (regs[regno].type != PTR_TO_STACK) {
+ if (zero_size_allowed && access_size == 0 &&
+ regs[regno].type == CONST_IMM &&
+ regs[regno].imm == 0)
+ return 0;
+
+ verbose("R%d type=%s expected=%s\n", regno,
+ reg_type_str[regs[regno].type],
+ reg_type_str[PTR_TO_STACK]);
return -EACCES;
+ }
off = regs[regno].imm;
if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
@@ -830,15 +839,24 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
return 0;
}
- if (arg_type == ARG_PTR_TO_STACK || arg_type == ARG_PTR_TO_MAP_KEY ||
+ if (arg_type == ARG_PTR_TO_MAP_KEY ||
arg_type == ARG_PTR_TO_MAP_VALUE) {
expected_type = PTR_TO_STACK;
- } else if (arg_type == ARG_CONST_STACK_SIZE) {
+ } else if (arg_type == ARG_CONST_STACK_SIZE ||
+ arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
expected_type = CONST_IMM;
} else if (arg_type == ARG_CONST_MAP_PTR) {
expected_type = CONST_PTR_TO_MAP;
} else if (arg_type == ARG_PTR_TO_CTX) {
expected_type = PTR_TO_CTX;
+ } else if (arg_type == ARG_PTR_TO_STACK) {
+ expected_type = PTR_TO_STACK;
+ /* One exception here. In case function allows for NULL to be
+ * passed in as argument, it's a CONST_IMM type. Final test
+ * happens during stack boundary checking.
+ */
+ if (reg->type == CONST_IMM && reg->imm == 0)
+ expected_type = CONST_IMM;
} else {
verbose("unsupported arg_type %d\n", arg_type);
return -EFAULT;
@@ -868,8 +886,8 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
verbose("invalid map_ptr to access map->key\n");
return -EACCES;
}
- err = check_stack_boundary(env, regno, (*mapp)->key_size);
-
+ err = check_stack_boundary(env, regno, (*mapp)->key_size,
+ false);
} else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
/* bpf_map_xxx(..., map_ptr, ..., value) call:
* check [value, value + map->value_size) validity
@@ -879,9 +897,12 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
verbose("invalid map_ptr to access map->value\n");
return -EACCES;
}
- err = check_stack_boundary(env, regno, (*mapp)->value_size);
+ err = check_stack_boundary(env, regno, (*mapp)->value_size,
+ false);
+ } else if (arg_type == ARG_CONST_STACK_SIZE ||
+ arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
+ bool zero_size_allowed = (arg_type == ARG_CONST_STACK_SIZE_OR_ZERO);
- } else if (arg_type == ARG_CONST_STACK_SIZE) {
/* bpf_xxx(..., buf, len) call will access 'len' bytes
* from stack pointer 'buf'. Check it
* note: regno == len, regno - 1 == buf
@@ -891,7 +912,8 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
verbose("ARG_CONST_STACK_SIZE cannot be first argument\n");
return -EACCES;
}
- err = check_stack_boundary(env, regno - 1, reg->imm);
+ err = check_stack_boundary(env, regno - 1, reg->imm,
+ zero_size_allowed);
}
return err;