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Commit aa9147c9 authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Linus Torvalds
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ptrace: make PTRACE_SEIZE set ptrace options specified in 'data' parameter 



This can be used to close a few corner cases in strace where we get
unwanted racy behavior after attach, but before we have a chance to set
options (the notorious post-execve SIGTRAP comes to mind), and removes
the need to track "did we set opts for this task" state in strace
internals.

While we are at it:

Make it possible to extend SEIZE in the future with more functionality
by passing non-zero 'addr' parameter.  To that end, error out if 'addr'
is non-zero.  PTRACE_ATTACH did not (and still does not) have such
check, and users (strace) do pass garbage there...  let's avoid
repeating this mistake with SEIZE.

Set all task->ptrace bits in one operation - before this change, we were
adding PT_SEIZED and PT_PTRACE_CAP with task->ptrace |= BIT ops.  This
was probably ok (not a bug), but let's be on a safer side.

Changes since v2: use (unsigned long) casts instead of (long) ones, move
PTRACE_SEIZE_DEVEL-related code to separate lines of code.

Signed-off-by: default avatarDenys Vlasenko <vda.linux@googlemail.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Cc: Pedro Alves <palves@redhat.com>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 86b6c1f3

kernel/ptrace.c

+21 −10
Original line number Diff line number Diff line
@@ -231,6 +231,7 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode) 
}



static int ptrace_attach(struct task_struct *task, long request,

			 unsigned long addr,

			 unsigned long flags)

{

	bool seize = (request == PTRACE_SEIZE);
@@ -238,19 +239,29 @@ static int ptrace_attach(struct task_struct *task, long request, 


	/*

	 * SEIZE will enable new ptrace behaviors which will be implemented

	 * gradually.  SEIZE_DEVEL is used to prevent applications

	 * gradually.  SEIZE_DEVEL bit is used to prevent applications

	 * expecting full SEIZE behaviors trapping on kernel commits which

	 * are still in the process of implementing them.

	 *

	 * Only test programs for new ptrace behaviors being implemented

	 * should set SEIZE_DEVEL.  If unset, SEIZE will fail with -EIO.

	 *

	 * Once SEIZE behaviors are completely implemented, this flag and

	 * the following test will be removed.

	 * Once SEIZE behaviors are completely implemented, this flag

	 * will be removed.

	 */

	retval = -EIO;

	if (seize && !(flags & PTRACE_SEIZE_DEVEL))

	if (seize) {

		if (addr != 0)

			goto out;

		if (!(flags & PTRACE_SEIZE_DEVEL))

			goto out;

		flags &= ~(unsigned long)PTRACE_SEIZE_DEVEL;

		if (flags & ~(unsigned long)PTRACE_O_MASK)

			goto out;

		flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);

	} else {

		flags = PT_PTRACED;

	}



	audit_ptrace(task);
@@ -282,11 +293,11 @@ static int ptrace_attach(struct task_struct *task, long request, 
	if (task->ptrace)

		goto unlock_tasklist;



	task->ptrace = PT_PTRACED;

	if (seize)

		task->ptrace |= PT_SEIZED;

		flags |= PT_SEIZED;

	if (ns_capable(task_user_ns(task), CAP_SYS_PTRACE))

		task->ptrace |= PT_PTRACE_CAP;

		flags |= PT_PTRACE_CAP;

	task->ptrace = flags;



	__ptrace_link(task, current);
@@ -879,7 +890,7 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr, 
	}



	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {

		ret = ptrace_attach(child, request, data);

		ret = ptrace_attach(child, request, addr, data);

		/*

		 * Some architectures need to do book-keeping after

		 * a ptrace attach.
@@ -1022,7 +1033,7 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, 
	}



	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {

		ret = ptrace_attach(child, request, data);

		ret = ptrace_attach(child, request, addr, data);

		/*

		 * Some architectures need to do book-keeping after

		 * a ptrace attach.