sysctl.c: fix underflow value setting risk in vm_table

Apart from subsystem specific .proc_handler handler, all ctl_tables with
extra1 and extra2 members set should use proc_dointvec_minmax instead of
proc_dointvec, or the limit set in extra* never work and potentially echo
underflow values(negative numbers) is likely make system unstable.

Especially vfs_cache_pressure and zone_reclaim_mode, -1 is apparently not
a valid value, but we can set to them.  And then kernel may crash.

# echo -1 > /proc/sys/vm/vfs_cache_pressure

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Lin Feng <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/sysctl.c

@@ -2962,7 +2962,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &block_dump,
 		.maxlen		= sizeof(block_dump),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
 	},
 	{
@@ -2970,7 +2970,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &sysctl_vfs_cache_pressure,
 		.maxlen		= sizeof(sysctl_vfs_cache_pressure),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
 	},
 #if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
@@ -2980,7 +2980,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &sysctl_legacy_va_layout,
 		.maxlen		= sizeof(sysctl_legacy_va_layout),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
 	},
 #endif
@@ -2990,7 +2990,7 @@ static struct ctl_table vm_table[] = {
 		.data		= &node_reclaim_mode,
 		.maxlen		= sizeof(node_reclaim_mode),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_ZERO,
 	},
 	{