Re: [PATCH bpf-next v2 1/2] bpf: Relax allowlist for css_task iter

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




On 10/24/23 4:43 AM, Chuyi Zhou wrote:


在 2023/10/24 14:23, Chuyi Zhou 写道:
Hello,

在 2023/10/24 14:08, Yonghong Song 写道:

On 10/23/23 10:52 PM, Chuyi Zhou wrote:
Hello,

在 2023/10/24 12:57, Alexei Starovoitov 写道:
On Mon, Oct 23, 2023 at 7:42 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:

The newly added open-coded css_task iter would try to hold the global css_set_lock in bpf_iter_css_task_new, so the bpf side has to be careful in where it allows to use this iter. The mainly concern is dead locking on css_set_lock. check_css_task_iter_allowlist() in verifier enforced css_task
can only be used in bpf_lsm hooks and sleepable bpf_iter.

This patch relax the allowlist for css_task iter. Any lsm and any iter (even non-sleepable) and any sleepable are safe since they would not hold
the css_set_lock before entering BPF progs context.

This patch also fixes the misused BPF_TRACE_ITER in
check_css_task_iter_allowlist which compared bpf_prog_type with
bpf_attach_type.

Fixes: 9c66dc94b62ae ("bpf: Introduce css_task open-coded iterator kfuncs")
Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
---
  kernel/bpf/verifier.c                         | 21 ++++++++++++-------
  .../selftests/bpf/progs/iters_task_failure.c  |  4 ++--
  2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e9bc5d4a25a1..9f209adc4ccb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11088,18 +11088,23 @@ static int process_kf_arg_ptr_to_rbtree_node(struct bpf_verifier_env *env,
&meta->arg_rbtree_root.field);
  }

+/*
+ * css_task iter allowlist is needed to avoid dead locking on css_set_lock.
+ * LSM hooks and iters (both sleepable and non-sleepable) are safe.
+ * Any sleepable progs are also safe since bpf_check_attach_target() enforce
+ * them can only be attached to some specific hook points.
+ */
  static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
  {
         enum bpf_prog_type prog_type = resolve_prog_type(env->prog);

-       switch (prog_type) {
-       case BPF_PROG_TYPE_LSM:
+       if (prog_type == BPF_PROG_TYPE_LSM)
                 return true;
-       case BPF_TRACE_ITER:
-               return env->prog->aux->sleepable;
-       default:
-               return false;
-       }
+
+       if (env->prog->expected_attach_type == BPF_TRACE_ITER)
+               return true;

I think the switch by prog_type has to stay.
Checking attach_type == BPF_TRACE_ITER without considering prog_type
is fragile. It likely works, but we don't do it anywhere else.
Let's stick to what is known to work.


IIUC, do you mean:

static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
{
    enum bpf_prog_type prog_type = resolve_prog_type(env->prog);

     switch (prog_type) {
     case BPF_PROG_TYPE_LSM:
         return true;
    case BPF_PROG_TYPE_TRACING:
        if (env->prog->expected_attach_type == BPF_TRACE_ITER)
            return true;
        return env->prog->aux->sleepable;


The above can be a fullthrough instead.


Sorry, what do you mean 'a fullthrough' ?
Do you mean we can check env->prog->aux->sleepable first and then fall back to check prog/attach type ?


I see...

Sorry for the above noise. I noticed verifier.c uses 'fallthrough' to avoid the build warning, so we can:

static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
{
    enum bpf_prog_type prog_type = resolve_prog_type(env->prog);

    switch (prog_type) {
    case BPF_PROG_TYPE_LSM:
        return true;
    case BPF_PROG_TYPE_TRACING:
        if (env->prog->expected_attach_type == BPF_TRACE_ITER)
            return true;
        fallthrough;
    default:
        return env->prog->aux->sleepable;
    }
}


The above LGTM.





[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux