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SubjectRe: [PATCH] apparmor: don't try to replace stale label in ptrace access check
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On 09/13/2018 09:12 AM, Jann Horn wrote:
> As a comment above begin_current_label_crit_section() explains,
> begin_current_label_crit_section() must run in sleepable context because
> when label_is_stale() is true, aa_replace_current_label() runs, which uses
> prepare_creds(), which can sleep.
> Until now, the ptrace access check (which runs with a task lock held)
> violated this rule.
>
> Also add a might_sleep() assertion to begin_current_label_crit_section(),
> because asserts are less likely to be ignored than comments.
>
> Signed-off-by: Jann Horn <jannh@google.com>

oh ouch, thanks Jann nice catch. I've pulled it into apparmor-next

Acked-by: John Johansen <john.johansen@canonical.com>


> ---
> I have tested that just the might_sleep() yells a lot, and adding the
> rest of the patch stops the yelling.
>
> security/apparmor/include/cred.h | 2 ++
> security/apparmor/lsm.c | 4 ++--
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/security/apparmor/include/cred.h b/security/apparmor/include/cred.h
> index e287b7d0d4be..265ae6641a06 100644
> --- a/security/apparmor/include/cred.h
> +++ b/security/apparmor/include/cred.h
> @@ -151,6 +151,8 @@ static inline struct aa_label *begin_current_label_crit_section(void)
> {
> struct aa_label *label = aa_current_raw_label();
>
> + might_sleep();
> +
> if (label_is_stale(label)) {
> label = aa_get_newest_label(label);
> if (aa_replace_current_label(label) == 0)
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index 8b8b70620bbe..e3f40c20b9b4 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -114,13 +114,13 @@ static int apparmor_ptrace_access_check(struct task_struct *child,
> struct aa_label *tracer, *tracee;
> int error;
>
> - tracer = begin_current_label_crit_section();
> + tracer = __begin_current_label_crit_section();
> tracee = aa_get_task_label(child);
> error = aa_may_ptrace(tracer, tracee,
> (mode & PTRACE_MODE_READ) ? AA_PTRACE_READ
> : AA_PTRACE_TRACE);
> aa_put_label(tracee);
> - end_current_label_crit_section(tracer);
> + __end_current_label_crit_section(tracer);
>
> return error;
> }
>

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