linux-kernel - echo 1 > /proc/sys/vm/compact_memory -> sh: write error: Bad address

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 27 Dec 2012 11:21:48 +0000
From:	Liu Hui-R64343 <r64343@...escale.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"mgorman@...e.de" <mgorman@...e.de>
Subject: echo 1 > /proc/sys/vm/compact_memory -> sh: write error: Bad address

I met one error when does the following command:

sh/$ echo 1 > /proc/sys/vm/compact_memory
sh/$ sh: write error: Bad address

After using strace, I find the following:
...
write(1, "1\n", 2)                              = 3
write(1, "", 4294967295)                = -1 EFAULT (Bad address)
write(2, "echo: write error: Bad address\n", 31echo: write error: Bad address
) = 31

>From the code, we can see it will return COMPACT_COMPLETE = 3 always when write.

/* Compact all nodes in the system */
static int compact_nodes(void)
{
        int nid;

        /* Flush pending updates to the LRU lists */
        lru_add_drain_all();

        for_each_online_node(nid)
                compact_node(nid);

        return COMPACT_COMPLETE;
}

/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;

/* This is the entry point for compacting all nodes via /proc/sys/vm */
int sysctl_compaction_handler(struct ctl_table *table, int write,
                        void __user *buffer, size_t *length, loff_t *ppos)
{
        if (write)
                return compact_nodes();

        return 0;
}

I think we can't simply return COMPACT_COMPLETE, instead, we need return *length.

The following patch can fix this issue:

diff --git a/mm/compaction.c b/mm/compaction.c
index c4bc5ac..d3cb27f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -732,8 +732,10 @@ int sysctl_compact_memory;
 int sysctl_compaction_handler(struct ctl_table *table, int write,
                        void __user *buffer, size_t *length, loff_t *ppos)
 {
-       if (write)
-               return compact_nodes();
+       if (write) {
+               compact_nodes();
+               return *length;
+       }

        return 0;
 }


Anyone can comment on it? Thanks a lot.

Happy Holiday.

Best Regards,
Jason Liu



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/