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bpf: split check_mem_access logic for map values 

Move the logic to check memory accesses to a PTR_TO_MAP_VALUE_ADJ from
check_mem_access() to a separate helper check_map_access_adj(). This
enables to use those checks in other parts of the verifier as well,
where boundaries on PTR_TO_MAP_VALUE_ADJ might need to be checked, for
example when checking helper function arguments. The same thing is
already happening for other types such as PTR_TO_PACKET and its
check_packet_access() helper.

The code has been copied verbatim, with the only difference of removing
the "off += reg->max_value" statement and moving the sum into the call
statement to check_map_access(), as that was only needed due to the
earlier common check_map_access() call.

Signed-off-by: Gianluca Borello <g.borello@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gianluca Borello 2017-01-09 10:19:46 -08:00 committed by David S. Miller
parent f3a3e248f3
commit dbcfe5f76d
1 changed files with 49 additions and 39 deletions
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88
kernel/bpf/verifier.c
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@ -635,6 +635,51 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno, int off,
return 0;
}
/* check read/write into an adjusted map element */
static int check_map_access_adj(struct bpf_verifier_env *env, u32 regno,
int off, int size)
{
struct bpf_verifier_state *state = &env->cur_state;
struct bpf_reg_state *reg = &state->regs[regno];
int err;
/* We adjusted the register to this map value, so we
* need to change off and size to min_value and max_value
* respectively to make sure our theoretical access will be
* safe.
*/
if (log_level)
print_verifier_state(state);
env->varlen_map_value_access = true;
/* The minimum value is only important with signed
* comparisons where we can't assume the floor of a
* value is 0. If we are using signed variables for our
* index'es we need to make sure that whatever we use
* will have a set floor within our range.
*/
if (reg->min_value < 0) {
verbose("R%d min value is negative, either use unsigned index or do a if (index >=0) check.\n",
regno);
return -EACCES;
}
err = check_map_access(env, regno, reg->min_value + off, size);
if (err) {
verbose("R%d min value is outside of the array range\n",
regno);
return err;
}
/* If we haven't set a max value then we need to bail
* since we can't be sure we won't do bad things.
*/
if (reg->max_value == BPF_REGISTER_MAX_RANGE) {
verbose("R%d unbounded memory access, make sure to bounds check any array access into a map\n",
regno);
return -EACCES;
}
return check_map_access(env, regno, reg->max_value + off, size);
}
#define MAX_PACKET_OFF 0xffff
static bool may_access_direct_pkt_data(struct bpf_verifier_env *env,
@ -775,45 +820,10 @@ static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
return -EACCES;
}
/* If we adjusted the register to this map value at all then we
* need to change off and size to min_value and max_value
* respectively to make sure our theoretical access will be
* safe.
*/
if (reg->type == PTR_TO_MAP_VALUE_ADJ) {
if (log_level)
print_verifier_state(state);
env->varlen_map_value_access = true;
/* The minimum value is only important with signed
* comparisons where we can't assume the floor of a
* value is 0. If we are using signed variables for our
* index'es we need to make sure that whatever we use
* will have a set floor within our range.
*/
if (reg->min_value < 0) {
verbose("R%d min value is negative, either use unsigned index or do a if (index >=0) check.\n",
regno);
return -EACCES;
}
err = check_map_access(env, regno, reg->min_value + off,
size);
if (err) {
verbose("R%d min value is outside of the array range\n",
regno);
return err;
}
/* If we haven't set a max value then we need to bail
* since we can't be sure we won't do bad things.
*/
if (reg->max_value == BPF_REGISTER_MAX_RANGE) {
verbose("R%d unbounded memory access, make sure to bounds check any array access into a map\n",
regno);
return -EACCES;
}
off += reg->max_value;
}
err = check_map_access(env, regno, off, size);
if (reg->type == PTR_TO_MAP_VALUE_ADJ)
err = check_map_access_adj(env, regno, off, size);
else
err = check_map_access(env, regno, off, size);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown_value(state->regs, value_regno);