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Subject[PATCH] UML - Fix setting of TIF_SIGPENDING
From: Bodo Stroesser <>

My older patch, that sets TIF_SIGPENDING after an ptrace-interception
in syscall_trace() is wrong.
Some syscalls want to be called without any signal pending. If a signal
is pending on syscall-entry, they immediately return with -ERESTARTNOINTR.
Thus, on return to user, the pending signals can be processed and the
kernel will lower eip by 2 to have the syscall restarted after that.
Since my change sets TIF_SIGPENDING on the entry and exit interception,
stracing such a syscall looped! Try "strace ls" to see what happens.
Fix: set TIF_SIGPENDING on the exit interception only. This avoids the
loop and is enough for security.

Signed-off-by: Bodo Stroesser <>
Signed-off-by: Jeff Dike <>

Index: 2.6.9/arch/um/kernel/ptrace.c
--- 2.6.9.orig/arch/um/kernel/ptrace.c 2004-12-01 23:43:11.000000000 -0500
+++ 2.6.9/arch/um/kernel/ptrace.c 2004-12-01 23:52:23.000000000 -0500
@@ -330,8 +330,8 @@
tracesysgood = (current->ptrace & PT_TRACESYSGOOD) && !is_singlestep;
ptrace_notify(SIGTRAP | (tracesysgood ? 0x80 : 0));

- /* force do_signal() --> is_syscall() */
- set_thread_flag(TIF_SIGPENDING);
+ if (entryexit) /* force do_signal() --> is_syscall() */
+ set_thread_flag(TIF_SIGPENDING);

/* this isn't the same as continuing with a signal, but it will do
* for normal use. strace only continues with a signal if the
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