Subject: [PATCH 1/2] signal: Factor copy_siginfo_to_external32 from copy_siginfo_to_user32

From: [email-masked] (Eric W. Biederman)
Date: Fri, 17 Apr 2020 16:09:22 -0500

To remove the use of set_fs in the coredump code there needs to be a
way to convert a kernel siginfo to a userspace compat siginfo.

Call that function copy_siginfo_to_compat and factor it out of
copy_siginfo_to_user32.

The existence of x32 complicates this code.  On x32 SIGCHLD uses 64bit
times for utime and stime.  As only SIGCHLD is affected and SIGCHLD
never causes a coredump I have avoided handling that case.

Signed-off-by: "Eric W. Biederman" <[email-masked]>
---
 include/linux/compat.h |   1 +
 kernel/signal.c        | 108 +++++++++++++++++++++++------------------
 2 files changed, 63 insertions(+), 46 deletions(-)

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 0480ba4db592..4962b254e550 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -402,6 +402,7 @@ long compat_get_bitmap(unsigned long *mask, const compat_ulong_t __user *umask,
 		       unsigned long bitmap_size);
 long compat_put_bitmap(compat_ulong_t __user *umask, unsigned long *mask,
 		       unsigned long bitmap_size);
+void copy_siginfo_to_external32(struct compat_siginfo *to, const struct kernel_siginfo *from);
 int copy_siginfo_from_user32(kernel_siginfo_t *to, const struct compat_siginfo __user *from);
 int copy_siginfo_to_user32(struct compat_siginfo __user *to, const kernel_siginfo_t *from);
 int get_compat_sigevent(struct sigevent *event,
diff --git a/kernel/signal.c b/kernel/signal.c
index e58a6c619824..578f196898cb 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3235,90 +3235,106 @@ int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from)
 }
 
 #ifdef CONFIG_COMPAT
-int copy_siginfo_to_user32(struct compat_siginfo __user *to,
-			   const struct kernel_siginfo *from)
-#if defined(CONFIG_X86_X32_ABI) || defined(CONFIG_IA32_EMULATION)
+void copy_siginfo_to_external32(struct compat_siginfo *to,
+				const struct kernel_siginfo *from)
 {
-	return __copy_siginfo_to_user32(to, from, in_x32_syscall());
-}
-int __copy_siginfo_to_user32(struct compat_siginfo __user *to,
-			     const struct kernel_siginfo *from, bool x32_ABI)
-#endif
-{
-	struct compat_siginfo new;
-	memset(&new, 0, sizeof(new));
+	/*
+	 * This function does not work properly for SIGCHLD on x32,
+	 * but it does not need to as SIGCHLD never causes a coredump.
+	 */
+	memset(to, 0, sizeof(*to));
 
-	new.si_signo = from->si_signo;
-	new.si_errno = from->si_errno;
-	new.si_code  = from->si_code;
+	to->si_signo = from->si_signo;
+	to->si_errno = from->si_errno;
+	to->si_code  = from->si_code;
 	switch(siginfo_layout(from->si_signo, from->si_code)) {
 	case SIL_KILL:
-		new.si_pid = from->si_pid;
-		new.si_uid = from->si_uid;
+		to->si_pid = from->si_pid;
+		to->si_uid = from->si_uid;
 		break;
 	case SIL_TIMER:
-		new.si_tid     = from->si_tid;
-		new.si_overrun = from->si_overrun;
-		new.si_int     = from->si_int;
+		to->si_tid     = from->si_tid;
+		to->si_overrun = from->si_overrun;
+		to->si_int     = from->si_int;
 		break;
 	case SIL_POLL:
-		new.si_band = from->si_band;
-		new.si_fd   = from->si_fd;
+		to->si_band = from->si_band;
+		to->si_fd   = from->si_fd;
 		break;
 	case SIL_FAULT:
-		new.si_addr = ptr_to_compat(from->si_addr);
+		to->si_addr = ptr_to_compat(from->si_addr);
 #ifdef __ARCH_SI_TRAPNO
-		new.si_trapno = from->si_trapno;
+		to->si_trapno = from->si_trapno;
 #endif
 		break;
 	case SIL_FAULT_MCEERR:
-		new.si_addr = ptr_to_compat(from->si_addr);
+		to->si_addr = ptr_to_compat(from->si_addr);
 #ifdef __ARCH_SI_TRAPNO
-		new.si_trapno = from->si_trapno;
+		to->si_trapno = from->si_trapno;
 #endif
-		new.si_addr_lsb = from->si_addr_lsb;
+		to->si_addr_lsb = from->si_addr_lsb;
 		break;
 	case SIL_FAULT_BNDERR:
-		new.si_addr = ptr_to_compat(from->si_addr);
+		to->si_addr = ptr_to_compat(from->si_addr);
 #ifdef __ARCH_SI_TRAPNO
-		new.si_trapno = from->si_trapno;
+		to->si_trapno = from->si_trapno;
 #endif
-		new.si_lower = ptr_to_compat(from->si_lower);
-		new.si_upper = ptr_to_compat(from->si_upper);
+		to->si_lower = ptr_to_compat(from->si_lower);
+		to->si_upper = ptr_to_compat(from->si_upper);
 		break;
 	case SIL_FAULT_PKUERR:
-		new.si_addr = ptr_to_compat(from->si_addr);
+		to->si_addr = ptr_to_compat(from->si_addr);
 #ifdef __ARCH_SI_TRAPNO
-		new.si_trapno = from->si_trapno;
+		to->si_trapno = from->si_trapno;
 #endif
-		new.si_pkey = from->si_pkey;
+		to->si_pkey = from->si_pkey;
 		break;
 	case SIL_CHLD:
-		new.si_pid    = from->si_pid;
-		new.si_uid    = from->si_uid;
-		new.si_status = from->si_status;
+		to->si_pid    = from->si_pid;
+		to->si_uid    = from->si_uid;
+		to->si_status = from->si_status;
+		to->si_utime = from->si_utime;
+		to->si_stime = from->si_stime;
 #ifdef CONFIG_X86_X32_ABI
 		if (x32_ABI) {
-			new._sifields._sigchld_x32._utime = from->si_utime;
-			new._sifields._sigchld_x32._stime = from->si_stime;
+			to->_sifields._sigchld_x32._utime = from->si_utime;
+			to->_sifields._sigchld_x32._stime = from->si_stime;
 		} else
 #endif
 		{
-			new.si_utime = from->si_utime;
-			new.si_stime = from->si_stime;
 		}
 		break;
 	case SIL_RT:
-		new.si_pid = from->si_pid;
-		new.si_uid = from->si_uid;
-		new.si_int = from->si_int;
+		to->si_pid = from->si_pid;
+		to->si_uid = from->si_uid;
+		to->si_int = from->si_int;
 		break;
 	case SIL_SYS:
-		new.si_call_addr = ptr_to_compat(from->si_call_addr);
-		new.si_syscall   = from->si_syscall;
-		new.si_arch      = from->si_arch;
+		to->si_call_addr = ptr_to_compat(from->si_call_addr);
+		to->si_syscall   = from->si_syscall;
+		to->si_arch      = from->si_arch;
 		break;
 	}
+}
+
+int copy_siginfo_to_user32(struct compat_siginfo __user *to,
+			   const struct kernel_siginfo *from)
+#if defined(CONFIG_X86_X32_ABI) || defined(CONFIG_IA32_EMULATION)
+{
+	return __copy_siginfo_to_user32(to, from, in_x32_syscall());
+}
+int __copy_siginfo_to_user32(struct compat_siginfo __user *to,
+			     const struct kernel_siginfo *from, bool x32_ABI)
+#endif
+{
+	struct compat_siginfo new;
+	copy_siginfo_to_external32(&new, from);
+#ifdef CONFIG_X86_X32_ABI
+	if (x32_ABI && from->si_signo == SIGCHLD) {
+		new._sifields._sigchld_x32._utime = from->si_utime;
+		new._sifields._sigchld_x32._stime = from->si_stime;
+	}
+#endif
 
 	if (copy_to_user(to, &new, sizeof(struct compat_siginfo)))
 		return -EFAULT;
-- 
2.25.0