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Commit 5534ecb2 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Frederic Weisbecker
Browse files

ptrace: kill BKL in ptrace syscall 



The comment suggests that this usage is stale. There is no bkl in the
exec path so if there is a race lurking there, the bkl in ptrace is
not going to help in this regard.

Overview of the possibility of "accidental" races this bkl might
protect:

- ptrace_traceme() is protected against task removal and concurrent
read/write on current->ptrace as it locks write tasklist_lock.

- arch_ptrace_attach() is serialized by ptrace_traceme() against
concurrent PTRACE_TRACEME or PTRACE_ATTACH

- ptrace_attach() is protected the same way ptrace_traceme() and
in turn serializes arch_ptrace_attach()

- ptrace_check_attach() does its own well described serializing too.

There is no obvious race here.

Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Roland McGrath <roland@redhat.com>
parent 2eaa9cfd

kernel/ptrace.c

+0 −10
Original line number Original line Diff line number Diff line
@@ -666,10 +666,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data) 
	struct task_struct *child;

	struct task_struct *child;

	long ret;

	long ret;





	/*

	 * This lock_kernel fixes a subtle race with suid exec

	 */

	lock_kernel();

	if (request == PTRACE_TRACEME) {

	if (request == PTRACE_TRACEME) {

		ret = ptrace_traceme();

		ret = ptrace_traceme();

		if (!ret)

		if (!ret)
@@ -703,7 +699,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, long, addr, long, data) 
 out_put_task_struct:

 out_put_task_struct:

	put_task_struct(child);

	put_task_struct(child);

 out:

 out:

	unlock_kernel();

	return ret;

	return ret;

}

}
@@ -813,10 +808,6 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, 
	struct task_struct *child;

	struct task_struct *child;

	long ret;

	long ret;





	/*

	 * This lock_kernel fixes a subtle race with suid exec

	 */

	lock_kernel();

	if (request == PTRACE_TRACEME) {

	if (request == PTRACE_TRACEME) {

		ret = ptrace_traceme();

		ret = ptrace_traceme();

		goto out;

		goto out;
@@ -846,7 +837,6 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, 
 out_put_task_struct:

 out_put_task_struct:

	put_task_struct(child);

	put_task_struct(child);

 out:

 out:

	unlock_kernel();

	return ret;

	return ret;

}

}

#endif	/* CONFIG_COMPAT */
 
#endif	/* CONFIG_COMPAT */