From: Youlin Li liulin063@gmail.com
[ Upstream commit f1db20814af532f85e091231223e5e4818e8464b ]
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: fd978bf7fd31 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7bfeb249214e..69fb46fdf763 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6552,8 +6552,12 @@ 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;