[PATCH 04/97] mm: prevent setting of a value less than 0 to min_free_kbytes

From: Mel Gorman
Date: Thu Aug 28 2014 - 15:07:57 EST

From: Han Pingtian <hanpt@xxxxxxxxxxxxxxxxxx>

commit da8c757b080ee84f219fa2368cb5dd23ac304fc0 upstream.

If echo -1 > /proc/vm/sys/min_free_kbytes, the system will hang. Changing
proc_dointvec() to proc_dointvec_minmax() in the
min_free_kbytes_sysctl_handler() can prevent this to happen.

mhocko said:

: You can still do echo $BIG_VALUE > /proc/vm/sys/min_free_kbytes and make
: your machine unusable but I agree that proc_dointvec_minmax is more
: suitable here as we already have:
: .proc_handler = min_free_kbytes_sysctl_handler,
: .extra1 = &zero,
: It used to work properly but then 6fce56ec91b5 ("sysctl: Remove references
: to ctl_name and strategy from the generic sysctl table") has removed
: sysctl_intvec strategy and so extra1 is ignored.

Signed-off-by: Han Pingtian <hanpt@xxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
mm/page_alloc.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e0a9cf..bffedeb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5734,7 +5734,12 @@ module_init(init_per_zone_wmark_min)
int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
- proc_dointvec(table, write, buffer, length, ppos);
+ int rc;
+ rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (rc)
+ return rc;
if (write) {
user_min_free_kbytes = min_free_kbytes;

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