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>

4 files changed, 10 insertions, 0 deletions

diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index 2e02aef5a334..f5f154942aab 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -881,6 +881,7 @@ SYSCALL_DEFINE5(osf_setsysinfo, unsigned long, op, void __user *, buffer,
 			if (fex & IEEE_TRAP_ENABLE_DZE) si_code = FPE_FLTDIV;
 			if (fex & IEEE_TRAP_ENABLE_INV) si_code = FPE_FLTINV;
 
+			clear_siginfo(&info);
 			info.si_signo = SIGFPE;
 			info.si_errno = 0;
 			info.si_code = si_code;
diff --git a/arch/alpha/kernel/signal.c b/arch/alpha/kernel/signal.c
index 9ebb3bcbc626..cd306e602313 100644
--- a/arch/alpha/kernel/signal.c
+++ b/arch/alpha/kernel/signal.c
@@ -221,6 +221,7 @@ do_sigreturn(struct sigcontext __user *sc)
 	if (ptrace_cancel_bpt (current)) {
 		siginfo_t info;
 
+		clear_siginfo(&info);
 		info.si_signo = SIGTRAP;
 		info.si_errno = 0;
 		info.si_code = TRAP_BRKPT;
@@ -255,6 +256,7 @@ do_rt_sigreturn(struct rt_sigframe __user *frame)
 	if (ptrace_cancel_bpt (current)) {
 		siginfo_t info;
 
+		clear_siginfo(&info);
 		info.si_signo = SIGTRAP;
 		info.si_errno = 0;
 		info.si_code = TRAP_BRKPT;
diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
index f43bd05dede2..91636765dd6d 100644
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -228,6 +228,7 @@ do_entArith(unsigned long summary, unsigned long write_mask,
 	}
 	die_if_kernel("Arithmetic fault", regs, 0, NULL);
 
+	clear_siginfo(&info);
 	info.si_signo = SIGFPE;
 	info.si_errno = 0;
 	info.si_code = si_code;
@@ -241,6 +242,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
 	siginfo_t info;
 	int signo, code;
 
+	clear_siginfo(&info);
 	if ((regs->ps & ~IPL_MAX) == 0) {
 		if (type == 1) {
 			const unsigned int *data
@@ -430,6 +432,7 @@ do_entDbg(struct pt_regs *regs)
 
 	die_if_kernel("Instruction fault", regs, 0, NULL);
 
+	clear_siginfo(&info);
 	info.si_signo = SIGILL;
 	info.si_errno = 0;
 	info.si_code = ILL_ILLOPC;
@@ -761,6 +764,8 @@ do_entUnaUser(void __user * va, unsigned long opcode,
 	siginfo_t info;
 	long error;
 
+	clear_siginfo(&info);
+
 	/* Check the UAC bits to decide what the user wants us to do
 	   with the unaliged access.  */
 
diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index cd3c572ee912..7f2202a9f50a 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -91,6 +91,8 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 	siginfo_t info;
 	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
+	clear_siginfo(&info);
+
 	/* As of EV6, a load into $31/$f31 is a prefetch, and never faults
 	   (or is suppressed by the PALcode).  Support that for older CPUs
 	   by ignoring such an instruction.  */