ptrace: the killed tracee should not enter the syscall

Another old/known problem.  If the tracee is killed after it reports
syscall_entry, it starts the syscall and debugger can't control this.
This confuses the users and this creates the security problems for
ptrace jailers.

Change tracehook_report_syscall_entry() to return non-zero if killed,
this instructs syscall_trace_enter() to abort the syscall.

Reported-by: Chris Evans <[email protected]>
Tested-by: Indan Zupancic <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Pedro Alves <[email protected]>
Cc: Jan Kratochvil <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index a71a2927a6a0..51bd91d911c3 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -54,12 +54,12 @@ struct linux_binprm;
 /*
  * ptrace report for syscall entry and exit looks identical.
  */
-static inline void ptrace_report_syscall(struct pt_regs *regs)
+static inline int ptrace_report_syscall(struct pt_regs *regs)
 {
 	int ptrace = current->ptrace;
 
 	if (!(ptrace & PT_PTRACED))
-		return;
+		return 0;
 
 	ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
 
@@ -72,6 +72,8 @@ static inline void ptrace_report_syscall(struct pt_regs *regs)
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
+
+	return fatal_signal_pending(current);
 }
 
 /**
@@ -96,8 +98,7 @@ static inline void ptrace_report_syscall(struct pt_regs *regs)
 static inline __must_check int tracehook_report_syscall_entry(
 	struct pt_regs *regs)
 {
-	ptrace_report_syscall(regs);
-	return 0;
+	return ptrace_report_syscall(regs);
 }
 
 /**