mm: prevent setting of a value less than 0 to min_free_kbytes

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@linux.vnet.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a280f772bc6661b4f0c23ad57daf02630d2cccdb..95f20173abbad49cc99fa9bff9d6b4a3c5c91fd2 100644 (file)
--- 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;
                setup_per_zone_wmarks();