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    Subject[PATCH 4.19 026/639] apparmor: dont try to replace stale label in ptrace access check
    Date
    From: Jann Horn <jannh@google.com>

    [ Upstream commit 1f8266ff58840d698a1e96d2274189de1bdf7969 ]

    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.

    Fixes: b2d09ae449ced ("apparmor: move ptrace checks to using labels")
    Signed-off-by: Jann Horn <jannh@google.com>
    Signed-off-by: John Johansen <john.johansen@canonical.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 e287b7d0d4beb..265ae6641a064 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 590ca7d8fae54..730de4638b4e2 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;
    }
    --
    2.20.1


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