[87/90] sysctl_max_map_count should be non-negative

[Greg KH]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Amerigo Wang <amwang@xxxxxxxxxx>

commit 70da2340fbc68e91e701762f785479ab495a0869 upstream.

Jan Engelhardt reported we have this problem:

setting max_map_count to a value large enough results in programs dying at
first try.  This is on 2.6.31.6:

15:59 borg:/proc/sys/vm # echo $[1<<31-1] >max_map_count
15:59 borg:/proc/sys/vm # cat max_map_count
1073741824
15:59 borg:/proc/sys/vm # echo $[1<<31] >max_map_count
15:59 borg:/proc/sys/vm # cat max_map_count
Killed

This is because we have a chance to make 'max_map_count' negative.  but
it's meaningless.  Make it only accept non-negative values.

Reported-by: Jan Engelhardt <jengelh@xxxxxxxxxx>
Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/sysctl.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1539,7 +1539,8 @@ static struct ctl_table debug_table[] = 
 		.data		= &show_unhandled_signals,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec
+		.proc_handler	= proc_dointvec,
+		.extra1		= &zero,
 	},
 #endif
 	{ .ctl_name = 0 }


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