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authorOleg Nesterov <oleg@redhat.com>2009-06-17 16:27:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-18 13:03:51 -0700
commit4b105cbbaf7c06e01c27391957dc3c446328d087 (patch)
tree4b6a65061a7bf46baea9d8867fdda0c22c8a3d45 /kernel/ptrace.c
parentf2f0b00ad61d53adfecb8bdf8f3cf8f05f6ed548 (diff)
downloadlinux-2.6.34-ux500-4b105cbbaf7c06e01c27391957dc3c446328d087.tar.gz
ptrace: do not use task_lock() for attach
Remove the "Nasty, nasty" lock dance in ptrace_attach()/ptrace_traceme() - from now task_lock() has nothing to do with ptrace at all. With the recent changes nobody uses task_lock() to serialize with ptrace, but in fact it was never needed and it was never used consistently. However ptrace_attach() calls __ptrace_may_access() and needs task_lock() to pin task->mm for get_dumpable(). But we can call __ptrace_may_access() before we take tasklist_lock, ->cred_exec_mutex protects us against do_execve() path which can change creds and MMF_DUMP* flags. (ugly, but we can't use ptrace_may_access() because it hides the error code, so we have to take task_lock() and use __ptrace_may_access()). NOTE: this change assumes that LSM hooks, security_ptrace_may_access() and security_ptrace_traceme(), can be called without task_lock() held. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Chris Wright <chrisw@sous-sol.org> Acked-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c59
1 files changed, 13 insertions, 46 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 12e21a949db..38fdfea1a15 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -167,7 +167,6 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode)
int ptrace_attach(struct task_struct *task)
{
int retval;
- unsigned long flags;
audit_ptrace(task);
@@ -185,34 +184,19 @@ int ptrace_attach(struct task_struct *task)
retval = mutex_lock_interruptible(&task->cred_guard_mutex);
if (retval < 0)
goto out;
-repeat:
- /*
- * Nasty, nasty.
- *
- * We want to hold both the task-lock and the
- * tasklist_lock for writing at the same time.
- * But that's against the rules (tasklist_lock
- * is taken for reading by interrupts on other
- * cpu's that may have task_lock).
- */
- task_lock(task);
- if (!write_trylock_irqsave(&tasklist_lock, flags)) {
- task_unlock(task);
- do {
- cpu_relax();
- } while (!write_can_lock(&tasklist_lock));
- goto repeat;
- }
+ task_lock(task);
retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
+ task_unlock(task);
if (retval)
- goto bad;
+ goto unlock_creds;
+ write_lock_irq(&tasklist_lock);
retval = -EPERM;
if (unlikely(task->exit_state))
- goto bad;
+ goto unlock_tasklist;
if (task->ptrace)
- goto bad;
+ goto unlock_tasklist;
task->ptrace = PT_PTRACED;
if (capable(CAP_SYS_PTRACE))
@@ -222,9 +206,9 @@ repeat:
send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
retval = 0;
-bad:
- write_unlock_irqrestore(&tasklist_lock, flags);
- task_unlock(task);
+unlock_tasklist:
+ write_unlock_irq(&tasklist_lock);
+unlock_creds:
mutex_unlock(&task->cred_guard_mutex);
out:
return retval;
@@ -240,26 +224,10 @@ int ptrace_traceme(void)
{
int ret = -EPERM;
- /*
- * Are we already being traced?
- */
-repeat:
- task_lock(current);
+ write_lock_irq(&tasklist_lock);
+ /* Are we already being traced? */
if (!current->ptrace) {
- /*
- * See ptrace_attach() comments about the locking here.
- */
- unsigned long flags;
- if (!write_trylock_irqsave(&tasklist_lock, flags)) {
- task_unlock(current);
- do {
- cpu_relax();
- } while (!write_can_lock(&tasklist_lock));
- goto repeat;
- }
-
ret = security_ptrace_traceme(current->parent);
-
/*
* Check PF_EXITING to ensure ->real_parent has not passed
* exit_ptrace(). Otherwise we don't report the error but
@@ -269,10 +237,9 @@ repeat:
current->ptrace = PT_PTRACED;
__ptrace_link(current, current->real_parent);
}
-
- write_unlock_irqrestore(&tasklist_lock, flags);
}
- task_unlock(current);
+ write_unlock_irq(&tasklist_lock);
+
return ret;
}