[PATCH] fix uts sysctl write size

From: Andy Whitcroft <apw@shadowen.org>

The sysctl interfaces for updating the uts entries such as hostname and
domainname are using the wrong length for these buffers; they are hard
coded to 64.  Although safe, this artifically limits the size of these
fields to one less than the true maximum.  This generates an inconsistency
between the various methods of update for these fields.

# hostname 12345678901234567890123456789012345678901234567890123456789012345
hostname: name too long
# hostname 1234567890123456789012345678901234567890123456789012345678901234
# hostname
1234567890123456789012345678901234567890123456789012345678901234

# sysctl -w kernel.hostname=1234567890123456789012345678901234567890123456789012345678901234567890
kernel.hostname = 1234567890123456789012345678901234567890123456789012345678901234567890
# hostname
123456789012345678901234567890123456789012345678901234567890123
#

The error originates from the fact the handler for strings (proc_dostring)
already allows for the string terminator.  This patch corrects the limit,
taking the oppotunity to convert to use of sizeof().
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sysctl.c

@@ -218,7 +218,7 @@ static ctl_table kern_table[] = {
 		.ctl_name	= KERN_OSTYPE,
 		.procname	= "ostype",
 		.data		= system_utsname.sysname,
-		.maxlen		= 64,
+		.maxlen		= sizeof(system_utsname.sysname),
 		.mode		= 0444,
 		.proc_handler	= &proc_doutsstring,
 		.strategy	= &sysctl_string,
@@ -227,7 +227,7 @@ static ctl_table kern_table[] = {
 		.ctl_name	= KERN_OSRELEASE,
 		.procname	= "osrelease",
 		.data		= system_utsname.release,
-		.maxlen		= 64,
+		.maxlen		= sizeof(system_utsname.release),
 		.mode		= 0444,
 		.proc_handler	= &proc_doutsstring,
 		.strategy	= &sysctl_string,
@@ -236,7 +236,7 @@ static ctl_table kern_table[] = {
 		.ctl_name	= KERN_VERSION,
 		.procname	= "version",
 		.data		= system_utsname.version,
-		.maxlen		= 64,
+		.maxlen		= sizeof(system_utsname.version),
 		.mode		= 0444,
 		.proc_handler	= &proc_doutsstring,
 		.strategy	= &sysctl_string,
@@ -245,7 +245,7 @@ static ctl_table kern_table[] = {
 		.ctl_name	= KERN_NODENAME,
 		.procname	= "hostname",
 		.data		= system_utsname.nodename,
-		.maxlen		= 64,
+		.maxlen		= sizeof(system_utsname.nodename),
 		.mode		= 0644,
 		.proc_handler	= &proc_doutsstring,
 		.strategy	= &sysctl_string,
@@ -254,7 +254,7 @@ static ctl_table kern_table[] = {
 		.ctl_name	= KERN_DOMAINNAME,
 		.procname	= "domainname",
 		.data		= system_utsname.domainname,
-		.maxlen		= 64,
+		.maxlen		= sizeof(system_utsname.domainname),
 		.mode		= 0644,
 		.proc_handler	= &proc_doutsstring,
 		.strategy	= &sysctl_string,