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From: Greg KH on 24 May 2010 19:20
2.6.34-stable review patch. If anyone has any objections, please let us know.

------------------

From: Gerald Schaefer <gerald.schaefer(a)de.ibm.com>

commit 545c174d1f093a462b4bb9131b23d5ea72a600e1 upstream.

strace may change the system call number, so regs->gprs[2] must not
be read before tracehook_report_syscall_entry(). This fixes a bug
where "strace -f" will hang after a vfork().

Signed-off-by: Gerald Schaefer <gerald.schaefer(a)de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky(a)de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
arch/s390/kernel/ptrace.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -632,7 +632,7 @@ long compat_arch_ptrace(struct task_stru

asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
{
- long ret;
+ long ret = 0;

/* Do the secure computing check first. */
secure_computing(regs->gprs[2]);
@@ -641,7 +641,6 @@ asmlinkage long do_syscall_trace_enter(s
* The sysc_tracesys code in entry.S stored the system
* call number to gprs[2].
*/
- ret = regs->gprs[2];
if (test_thread_flag(TIF_SYSCALL_TRACE) &&
(tracehook_report_syscall_entry(regs) ||
regs->gprs[2] >= NR_syscalls)) {
@@ -663,7 +662,7 @@ asmlinkage long do_syscall_trace_enter(s
regs->gprs[2], regs->orig_gpr2,
regs->gprs[3], regs->gprs[4],
regs->gprs[5]);
- return ret;
+ return ret ?: regs->gprs[2];
}

asmlinkage void do_syscall_trace_exit(struct pt_regs *regs)


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