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bpf: Fix wrong reg type conversion in release_reference()

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Some helper functions will allocate memory. To avoid memory leaks, the
verifier requires the eBPF program to release these memories by calling
the corresponding helper functions.

When a resource is released, all pointer registers corresponding to the
resource should be invalidated. The verifier use release_references() to
do this job, by apply  __mark_reg_unknown() to each relevant register.

It will give these registers the type of SCALAR_VALUE. A register that
will contain a pointer value at runtime, but of type SCALAR_VALUE, which
may allow the unprivileged user to get a kernel pointer by storing this
register into a map.

Using __mark_reg_not_init() while NOT allow_ptr_leaks can mitigate this
problem.

Fixes: fd978bf7fd ("bpf: Add reference tracking to verifier")
Signed-off-by: Youlin Li <liulin063@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221103093440.3161-1-liulin063@gmail.com
This commit is contained in:
Youlin Li 2022-11-03 17:34:39 +08:00 committed by Daniel Borkmann
parent 8bbabb3fdd
commit f1db20814a
1 changed files with 6 additions and 2 deletions
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8
kernel/bpf/verifier.c
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@ -6623,8 +6623,12 @@ static int release_reference(struct bpf_verifier_env *env,
return err;
bpf_for_each_reg_in_vstate(env->cur_state, state, reg, ({
if (reg->ref_obj_id == ref_obj_id)
__mark_reg_unknown(env, reg);
if (reg->ref_obj_id == ref_obj_id) {
if (!env->allow_ptr_leaks)
__mark_reg_not_init(env, reg);
else
__mark_reg_unknown(env, reg);
}
}));
return 0;