4.4-stable review patch. If anyone has any objections, please let me know.
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From: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com
commit 46725b17f1c6c815a41429259b3f070c01e71bc1 upstream.
When a uprobe is installed on an instruction that we currently do not emulate, we copy the instruction into a xol buffer and single step that instruction. If that instruction generates a fault, we abort the single stepping before invoking the signal handler. Once the signal handler is done, the uprobe trap is hit again since the instruction is retried and the process repeats.
We use uprobe_deny_signal() to detect if the xol instruction triggered a signal. If so, we clear TIF_SIGPENDING and set TIF_UPROBE so that the signal is not handled until after the single stepping is aborted. In this case, uprobe_deny_signal() returns true and get_signal() ends up returning 0. However, in do_signal(), we are not looking at the return value, but depending on ksig.sig for further action, all with an uninitialized ksig that is not touched in this scenario. Fix the same by initializing ksig.sig to 0.
Fixes: 129b69df9c90 ("powerpc: Use get_signal() signal_setup_done()") Reported-by: Anton Blanchard anton@samba.org Signed-off-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/kernel/signal.c +++ b/arch/powerpc/kernel/signal.c @@ -102,7 +102,7 @@ static void check_syscall_restart(struct static void do_signal(struct pt_regs *regs) { sigset_t *oldset = sigmask_to_save(); - struct ksignal ksig; + struct ksignal ksig = { .sig = 0 }; int ret; int is32 = is_32bit_task();