proc/sysctl: add shared variables for range check

In the sysctl code the proc_dointvec_minmax() function is often used to
validate the user supplied value between an allowed range.  This
function uses the extra1 and extra2 members from struct ctl_table as
minimum and maximum allowed value.

On sysctl handler declaration, in every source file there are some
readonly variables containing just an integer which address is assigned
to the extra1 and extra2 members, so the sysctl range is enforced.

The special values 0, 1 and INT_MAX are very often used as range
boundary, leading duplication of variables like zero=0, one=1,
int_max=INT_MAX in different source files:

    $ git grep -E '\.extra[12].*&(zero|one|int_max)' |wc -l
    248

Add a const int array containing the most commonly used values, some
macros to refer more easily to the correct array member, and use them
instead of creating a local one for every object file.

This is the bloat-o-meter output comparing the old and new binary
compiled with the default Fedora config:

    # scripts/bloat-o-meter -d vmlinux.o.old vmlinux.o
    add/remove: 2/2 grow/shrink: 0/2 up/down: 24/-188 (-164)
    Data                                         old     new   delta
    sysctl_vals                                    -      12     +12
    __kstrtab_sysctl_vals                          -      12     +12
    max                                           14      10      -4
    int_max                                       16       -     -16
    one                                           68       -     -68
    zero                                         128      28    -100
    Total: Before=20583249, After=20583085, chg -0.00%

[mcroce@redhat.com: tipc: remove two unused variables]
  Link: http://lkml.kernel.org/r/20190530091952.4108-1-mcroce@redhat.com
[akpm@linux-foundation.org: fix net/ipv6/sysctl_net_ipv6.c]
[arnd@arndb.de: proc/sysctl: make firmware loader table conditional]
  Link: http://lkml.kernel.org/r/20190617130014.1713870-1-arnd@arndb.de
[akpm@linux-foundation.org: fix fs/eventpoll.c]
Link: http://lkml.kernel.org/r/20190430180111.10688-1-mcroce@redhat.com
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 9 deletions

diff --git a/net/dccp/sysctl.c b/net/dccp/sysctl.c
index b59040f268a9..ee8d4f5afa72 100644
--- a/net/dccp/sysctl.c
+++ b/net/dccp/sysctl.c
@@ -16,9 +16,7 @@
 #endif
 
 /* Boundary values */
-static int		zero     = 0,
-			one      = 1,
-			u8_max   = 0xFF;
+static int		u8_max   = 0xFF;
 static unsigned long	seqw_min = DCCPF_SEQ_WMIN,
 			seqw_max = 0xFFFFFFFF;		/* maximum on 32 bit */
 
@@ -38,7 +36,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_rx_ccid),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= &u8_max,		/* RFC 4340, 10. */
 	},
 	{
@@ -47,7 +45,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_tx_ccid),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= &u8_max,		/* RFC 4340, 10. */
 	},
 	{
@@ -56,7 +54,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_request_retries),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &one,
+		.extra1		= SYSCTL_ONE,
 		.extra2		= &u8_max,
 	},
 	{
@@ -65,7 +63,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_retries1),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= &u8_max,
 	},
 	{
@@ -74,7 +72,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_retries2),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
+		.extra1		= SYSCTL_ZERO,
 		.extra2		= &u8_max,
 	},
 	{
@@ -83,7 +81,7 @@ static struct ctl_table dccp_default_table[] = {
 		.maxlen		= sizeof(sysctl_dccp_tx_qlen),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
+		.extra1		= SYSCTL_ZERO,
 	},
 	{
 		.procname	= "sync_ratelimit",