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bpf: Fix slot type check in check_stack_write_var_off

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For the case where allow_ptr_leaks is false, code is checking whether
slot type is STACK_INVALID and STACK_SPILL and rejecting other cases.
This is a consequence of incorrectly checking for register type instead
of the slot type (NOT_INIT and SCALAR_VALUE respectively). Fix the
check.

Fixes: 01f810ace9ed ("bpf: Allow variable-offset stack access")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221103191013.1236066-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-11-04 00:39:53 +05:30 committed by Alexei Starovoitov
parent 261f4664ca
commit f5e477a861
1 changed files with 11 additions and 8 deletions
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19
kernel/bpf/verifier.c
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@ -3181,14 +3181,17 @@ static int check_stack_write_var_off(struct bpf_verifier_env *env,
stype = &state->stack[spi].slot_type[slot % BPF_REG_SIZE];
mark_stack_slot_scratched(env, spi);
if (!env->allow_ptr_leaks
&& *stype != NOT_INIT
&& *stype != SCALAR_VALUE) {
/* Reject the write if there's are spilled pointers in
* range. If we didn't reject here, the ptr status
* would be erased below (even though not all slots are
* actually overwritten), possibly opening the door to
* leaks.
if (!env->allow_ptr_leaks && *stype != STACK_MISC && *stype != STACK_ZERO) {
/* Reject the write if range we may write to has not
* been initialized beforehand. If we didn't reject
* here, the ptr status would be erased below (even
* though not all slots are actually overwritten),
* possibly opening the door to leaks.
*
* We do however catch STACK_INVALID case below, and
* only allow reading possibly uninitialized memory
* later for CAP_PERFMON, as the write may not happen to
* that slot.
*/
verbose(env, "spilled ptr in range of var-offset stack write; insn %d, ptr off: %d",
insn_idx, i);