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: Denys Vlasenko <vda.linux@googlemail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Pedro Alves <palves@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 9acd07a..4661c5b 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -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))
-               goto out;
+       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.