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Subject[87/90] sysctl_max_map_count should be non-negative
2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Amerigo Wang <amwang@redhat.com>

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@medozas.de>
Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: James Morris <jmorris@namei.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
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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