ptrace: simplify PTRACE_foo constants and PTRACE_SETOPTIONS code

Exchange PT_TRACESYSGOOD and PT_PTRACE_CAP bit positions, which makes
PT_option bits contiguous and therefore makes code in
ptrace_setoptions() much simpler.

Every PTRACE_O_TRACEevent is defined to (1 << PTRACE_EVENT_event)
instead of using explicit numeric constants, to ensure we don't mess up
relationship between bit positions and event ids.

PT_EVENT_FLAG_SHIFT was not particularly useful, PT_OPT_FLAG_SHIFT with
value of PT_EVENT_FLAG_SHIFT-1 is easier to use.

PT_TRACE_MASK constant is nuked, the only its use is replaced by
(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Alves <palves@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, 8 insertions, 23 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 273f56ea39d2..9acd07a6f5bb 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -262,7 +262,7 @@ static int ptrace_attach(struct task_struct *task, long request,
 
         /*
          * Protect exec's credential calculations against our interference;
-         * interference; SUID, SGID and LSM creds get determined differently
+         * SUID, SGID and LSM creds get determined differently
          * under ptrace.
          */
         retval = -ERESTARTNOINTR;
@@ -528,31 +528,16 @@ int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long ds
 
 static int ptrace_setoptions(struct task_struct *child, unsigned long data)
 {
+        unsigned flags;
+
         if (data & ~(unsigned long)PTRACE_O_MASK)
                 return -EINVAL;
 
-        child->ptrace &= ~PT_TRACE_MASK;
-
-        if (data & PTRACE_O_TRACESYSGOOD)
-                child->ptrace |= PT_TRACESYSGOOD;
-
-        if (data & PTRACE_O_TRACEFORK)
-                child->ptrace |= PT_TRACE_FORK;
-
-        if (data & PTRACE_O_TRACEVFORK)
-                child->ptrace |= PT_TRACE_VFORK;
-
-        if (data & PTRACE_O_TRACECLONE)
-                child->ptrace |= PT_TRACE_CLONE;
-
-        if (data & PTRACE_O_TRACEEXEC)
-                child->ptrace |= PT_TRACE_EXEC;
-
-        if (data & PTRACE_O_TRACEVFORKDONE)
-                child->ptrace |= PT_TRACE_VFORK_DONE;
-
-        if (data & PTRACE_O_TRACEEXIT)
-                child->ptrace |= PT_TRACE_EXIT;
+        /* Avoid intermediate state when all opts are cleared */
+        flags = child->ptrace;
+        flags &= ~(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT);
+        flags |= (data << PT_OPT_FLAG_SHIFT);
+        child->ptrace = flags;
 
         return 0;
 }