Hi liqiong,

On 8/26/21 10:15 AM, liqiong wrote:

Hi Simon,

Thanks for your help, your advice is clear, can i just use it,
how about this:


The current IMA ruleset is identified by the variable "ima_rules",
and the pointer starts pointing at the list "ima_default_rules".

After reading it again, maybe
"The current IMA ruleset is identified by the variable "ima_rules",
that defaults to "&ima_default_rules".'?

When loading a custom policy for the first time, the variable is
updated to point to the list "ima_policy_rules" instead. That update
isn't RCU-safe, and deadlocks are possible.

I think what Mimi was trying to say is that you could add the high-level
overview above, but keep the details. Sorry if I wasn't clearer in my
earlier messages.

Consider re-adding your previous paragraph
"""
As a consequence, when traversing the ruleset, some functions like ima_match_policy()
may loop indefinitely over "ima_default_rules" as list_for_each_entry_rcu() doesn't
terminate (after the update, "ima_rules" no longer points to the list head, so the
loop condition stays always true), causing RCU stalls.
"""
(note: I tweaked it above, feel free to fix it)

Introduce a temporary value for "ima_rules" when iterating over
the ruleset to avoid the deadlocks.

... while keeping this a separate paragraph.