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| author | David Vernet <void@manifault.com> | 2023-01-25 15:38:10 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-01-25 16:57:49 +0100 |
| commit | caf713c338bd95bf9ac003d8985d2c4e46d452dd (patch) | |
| tree | 34e0b14bdee625598bbde4936ff473102883db00 /kernel/bpf | |
| parent | bpf: Allow trusted args to walk struct when checking BTF IDs (diff) | |
| download | linux-caf713c338bd95bf9ac003d8985d2c4e46d452dd.tar.xz linux-caf713c338bd95bf9ac003d8985d2c4e46d452dd.zip | |
bpf: Disallow NULLable pointers for trusted kfuncs
KF_TRUSTED_ARGS kfuncs currently have a subtle and insidious bug in
validating pointers to scalars. Say that you have a kfunc like the
following, which takes an array as the first argument:
bool bpf_cpumask_empty(const struct cpumask *cpumask)
{
return cpumask_empty(cpumask);
}
...
BTF_ID_FLAGS(func, bpf_cpumask_empty, KF_TRUSTED_ARGS)
...
If a BPF program were to invoke the kfunc with a NULL argument, it would
crash the kernel. The reason is that struct cpumask is defined as a
bitmap, which is itself defined as an array, and is accessed as a memory
address by bitmap operations. So when the verifier analyzes the
register, it interprets it as a pointer to a scalar struct, which is an
array of size 8. check_mem_reg() then sees that the register is NULL and
returns 0, and the kfunc crashes when it passes it down to the cpumask
wrappers.
To fix this, this patch adds a check for KF_ARG_PTR_TO_MEM which
verifies that the register doesn't contain a possibly-NULL pointer if
the kfunc is KF_TRUSTED_ARGS.
Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230125143816.721952-2-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 66ec577fcb8b..bb38b01b738f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9194,6 +9194,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ return -EINVAL; } + if (is_kfunc_trusted_args(meta) && + (register_is_null(reg) || type_may_be_null(reg->type))) { + verbose(env, "Possibly NULL pointer passed to trusted arg%d\n", i); + return -EACCES; + } + if (reg->ref_obj_id) { if (is_kfunc_release(meta) && meta->ref_obj_id) { verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n", |