linux-kernel - [PATCH 09/11] signal: Reduce copy

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Date:   Thu, 11 Jan 2018 18:59:38 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>, Oleg Nesterov <oleg@...hat.com>,
        linux-arch@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 09/11] signal: Reduce copy_siginfo to just a memcpy

The savings for copying just part of struct siginfo appears to be in the
noise on modern machines.  So remove this ``optimization'' and simplify the code.

At the same time mark the second parameter as constant so there is no confusion
as to which direction the copy will go.

This ensures that a fully initialized siginfo that is sent ends up as
a fully initialized siginfo on the signal queue.  This full initialization
ensures even confused code won't copy unitialized data to userspace, and
it prepares for turning copy_siginfo_to_user into a simple copy_to_user.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 include/linux/signal.h | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 042968dd98f0..8037b503ce91 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -11,13 +11,9 @@ struct task_struct;
 /* for sysctl */
 extern int print_fatal_signals;

-static inline void copy_siginfo(struct siginfo *to, struct siginfo *from)
+static inline void copy_siginfo(struct siginfo *to, const struct siginfo *from)
 {
-	if (from->si_code < 0)
-		memcpy(to, from, sizeof(*to));
-	else
-		/* _sigchld is currently the largest know union member */
-		memcpy(to, from, __ARCH_SI_PREAMBLE_SIZE + sizeof(from->_sifields._sigchld));
+	memcpy(to, from, sizeof(*to));
 }

 int copy_siginfo_to_user(struct siginfo __user *to, const struct siginfo *from);
-- 
2.14.1