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>

1 files changed, 21 insertions, 10 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 9acd07a6f5bb..4661c5bc07e5 100644
--- 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.