The patch titled
audit: call tty_audit_push_task() outside preempt disabled
has been added to the -mm tree. Its filename is
audit-call-tty_audit_push_task-outside-preempt-disabled.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: audit: call tty_audit_push_task() outside preempt disabled
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
While auditing all tasklist_lock read_lock sites I stumbled over the
following call chain:
audit_prepare_user_tty()
read_lock(&tasklist_lock);
tty_audit_push_task();
mutex_lock(&buf->mutex);
--> buf->mutex is locked with preemption disabled.
Solve this by acquiring a reference to the task struct under rcu_read_lock
and call tty_audit_push_task outside of the preempt disabled region.
Move all code which needs to be protected by sighand lock into
tty_audit_push_task() and use lock/unlock_sighand as we do not hold
tasklist_lock.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/tty_audit.c | 38 +++++++++++++++++++++++++++----------
include/linux/tty.h | 8 +------
kernel/audit.c | 25 ++++++++----------------
3 files changed, 39 insertions(+), 32 deletions(-)
diff -puN drivers/char/tty_audit.c~audit-call-tty_audit_push_task-outside-preempt-disabled drivers/char/tty_audit.c
--- a/drivers/char/tty_audit.c~audit-call-tty_audit_push_task-outside-preempt-disabled
+++ a/drivers/char/tty_audit.c
@@ -188,25 +188,43 @@ void tty_audit_tiocsti(struct tty_struct
}
/**
- * tty_audit_push_task - Flush task's pending audit data
+ * tty_audit_push_task - Flush task's pending audit data
+ * @tsk: task pointer
+ * @loginuid: sender login uid
+ * @sessionid: sender session id
+ *
+ * Called with a ref on @tsk held. Try to lock sighand and get a
+ * reference to the tty audit buffer if available.
+ * Flush the buffer or return an appropriate error code.
*/
-void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
+int tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
{
- struct tty_audit_buf *buf;
+ struct tty_audit_buf *buf = ERR_PTR(-EPERM);
+ unsigned long flags;
- spin_lock_irq(&tsk->sighand->siglock);
- buf = tsk->signal->tty_audit_buf;
- if (buf)
- atomic_inc(&buf->count);
- spin_unlock_irq(&tsk->sighand->siglock);
- if (!buf)
- return;
+ if (!lock_task_sighand(tsk, &flags))
+ return -ESRCH;
+
+ if (tsk->signal->audit_tty) {
+ buf = tsk->signal->tty_audit_buf;
+ if (buf)
+ atomic_inc(&buf->count);
+ }
+ unlock_task_sighand(tsk, &flags);
+
+ /*
+ * Return 0 when signal->audit_tty set
+ * but tsk->signal->tty_audit_buf == NULL.
+ */
+ if (!buf || IS_ERR(buf))
+ return PTR_ERR(buf);
mutex_lock(&buf->mutex);
tty_audit_buf_push(tsk, loginuid, sessionid, buf);
mutex_unlock(&buf->mutex);
tty_audit_buf_put(buf);
+ return 0;
}
/**
diff -puN include/linux/tty.h~audit-call-tty_audit_push_task-outside-preempt-disabled include/linux/tty.h
--- a/include/linux/tty.h~audit-call-tty_audit_push_task-outside-preempt-disabled
+++ a/include/linux/tty.h
@@ -540,8 +540,8 @@ extern void tty_audit_exit(void);
extern void tty_audit_fork(struct signal_struct *sig);
extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
extern void tty_audit_push(struct tty_struct *tty);
-extern void tty_audit_push_task(struct task_struct *tsk,
- uid_t loginuid, u32 sessionid);
+extern int tty_audit_push_task(struct task_struct *tsk,
+ uid_t loginuid, u32 sessionid);
#else
static inline void tty_audit_add_data(struct tty_struct *tty,
unsigned char *data, size_t size)
@@ -559,10 +559,6 @@ static inline void tty_audit_fork(struct
static inline void tty_audit_push(struct tty_struct *tty)
{
}
-static inline void tty_audit_push_task(struct task_struct *tsk,
- uid_t loginuid, u32 sessionid)
-{
-}
#endif
/* tty_io.c */
diff -puN kernel/audit.c~audit-call-tty_audit_push_task-outside-preempt-disabled kernel/audit.c
--- a/kernel/audit.c~audit-call-tty_audit_push_task-outside-preempt-disabled
+++ a/kernel/audit.c
@@ -467,23 +467,16 @@ static int audit_prepare_user_tty(pid_t
struct task_struct *tsk;
int err;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
tsk = find_task_by_vpid(pid);
- err = -ESRCH;
- if (!tsk)
- goto out;
- err = 0;
-
- spin_lock_irq(&tsk->sighand->siglock);
- if (!tsk->signal->audit_tty)
- err = -EPERM;
- spin_unlock_irq(&tsk->sighand->siglock);
- if (err)
- goto out;
-
- tty_audit_push_task(tsk, loginuid, sessionid);
-out:
- read_unlock(&tasklist_lock);
+ if (!tsk) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
+ get_task_struct(tsk);
+ rcu_read_unlock();
+ err = tty_audit_push_task(tsk, loginuid, sessionid);
+ put_task_struct(tsk);
return err;
}
_
Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are
linux-next.patch
audit-call-tty_audit_push_task-outside-preempt-disabled.patch
audit-do-not-send-uninitialized-data-for-audit_tty_get.patch
audit-use-rcu-for-task-lookup-protection.patch
time-compensate-for-rounding-on-odd-frequency-clocksources.patch
x86-enable-arch_dma_addr_t_64bit-with-x86_64-highmem64g.patch
hpet-fix-unwanted-interrupt-due-to-stale-irq-status-bit.patch
hpet-factor-timer-allocate-from-open.patch
timer_list-remove-alignment-padding-on-64-bit-when-config_timer_stats.patch
timer-initialize-the-field-slack-of-timer_list.patch
kernel-time-use-array_size-macro-in-timecomparec.patch
sched-make-sched_param-argument-static-variables-in-some-sched_setscheduler-caller.patch
kernelh-add-minmax3-macros.patch
kernelh-add-minmax3-macros-fix.patch
replace-nested-max-min-macros-with-maxmin3-macro.patch
add-the-common-dma_addr_t-typedef-to-include-linux-typesh.patch
select-rename-estimate_accuracy-to-select_estimate_accuracy.patch
epoll-make-epoll_wait-use-the-hrtimer-range-feature.patch
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