signal: Ensure every siginfo we send has all bits initialized

Call clear_siginfo to ensure every stack allocated siginfo is properly
initialized before being passed to the signal sending functions.

Note: It is not safe to depend on C initializers to initialize struct
siginfo on the stack because C is allowed to skip holes when
initializing a structure.

The initialization of struct siginfo in tracehook_report_syscall_exit
was moved from the helper user_single_step_siginfo into
tracehook_report_syscall_exit itself, to make it clear that the local
variable siginfo gets fully initialized.

In a few cases the scope of struct siginfo has been reduced to make it
clear that siginfo siginfo is not used on other paths in the function
in which it is declared.

Instances of using memset to initialize siginfo have been replaced
with calls clear_siginfo for clarity.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

6 files changed, 8 insertions, 2 deletions

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 70b7845434cb..7782cdbcd67d 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -107,7 +107,7 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
 		thread->cr2		= ptr;
 		thread->trap_nr		= X86_TRAP_PF;
 
-		memset(&info, 0, sizeof(info));
+		clear_siginfo(&info);
 		info.si_signo		= SIGSEGV;
 		info.si_errno		= 0;
 		info.si_code		= SEGV_MAPERR;
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index ed5c4cdf0a34..e2ee403865eb 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1377,7 +1377,6 @@ static void fill_sigtrap_info(struct task_struct *tsk,
 	tsk->thread.trap_nr = X86_TRAP_DB;
 	tsk->thread.error_code = error_code;
 
-	memset(info, 0, sizeof(*info));
 	info->si_signo = SIGTRAP;
 	info->si_code = si_code;
 	info->si_addr = user_mode(regs) ? (void __user *)regs->ip : NULL;
@@ -1395,6 +1394,7 @@ void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
 {
 	struct siginfo info;
 
+	clear_siginfo(&info);
 	fill_sigtrap_info(tsk, regs, error_code, si_code, &info);
 	/* Send us the fake SIGTRAP */
 	force_sig_info(SIGTRAP, &info, tsk);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 03f3d7695dac..a535dd64de63 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -299,6 +299,7 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
 	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
 			NOTIFY_STOP) {
 		cond_local_irq_enable(regs);
+		clear_siginfo(&info);
 		do_trap(trapnr, signr, str, regs, error_code,
 			fill_trap_info(regs, signr, trapnr, &info));
 	}
@@ -854,6 +855,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 
 	task->thread.trap_nr	= trapnr;
 	task->thread.error_code = error_code;
+	clear_siginfo(&info);
 	info.si_signo		= SIGFPE;
 	info.si_errno		= 0;
 	info.si_addr		= (void __user *)uprobe_get_trap_addr(regs);
@@ -929,6 +931,7 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 	local_irq_enable();
 
+	clear_siginfo(&info);
 	info.si_signo = SIGILL;
 	info.si_errno = 0;
 	info.si_code = ILL_BADSTK;
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index f44ce0fb3583..ff20b35e98dd 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -278,6 +278,7 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
 	tsk->thread.error_code	= X86_PF_USER | X86_PF_WRITE;
 	tsk->thread.trap_nr	= X86_TRAP_PF;
 
+	clear_siginfo(&info);
 	info.si_signo	= SIGSEGV;
 	info.si_errno	= 0;
 	info.si_code	= SEGV_MAPERR;
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 8494dbae41b9..d634f0332c0f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3007,6 +3007,7 @@ static void kvm_send_hwpoison_signal(unsigned long address, struct task_struct *
 {
 	siginfo_t info;
 
+	clear_siginfo(&info);
 	info.si_signo	= SIGBUS;
 	info.si_errno	= 0;
 	info.si_code	= BUS_MCEERR_AR;
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 73bd8c95ac71..2a5a2920203d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -209,6 +209,7 @@ force_sig_info_fault(int si_signo, int si_code, unsigned long address,
 	unsigned lsb = 0;
 	siginfo_t info;
 
+	clear_siginfo(&info);
 	info.si_signo	= si_signo;
 	info.si_errno	= 0;
 	info.si_code	= si_code;