[PATCH 3.2 192/221] gen_stats.c: Duplicate xstats buffer for later use

[Ben Hutchings]

3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ignacy GawÄdzki  <ignacy.gawedzki@xxxxxxxxxxxxxxxxxxxxxxx>

[ Upstream commit 1c4cff0cf55011792125b6041bc4e9713e46240f ]

The gnet_stats_copy_app() function gets called, more often than not, with its
second argument a pointer to an automatic variable in the caller's stack.
Therefore, to avoid copying garbage afterwards when calling
gnet_stats_finish_copy(), this data is better copied to a dynamically allocated
memory that gets freed after use.

[xiyou.wangcong@xxxxxxxxx: remove a useless kfree()]

Signed-off-by: Ignacy GawÄdzki <ignacy.gawedzki@xxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/core/gen_stats.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

--- a/net/core/gen_stats.c
+++ b/net/core/gen_stats.c
@@ -31,6 +31,9 @@ gnet_stats_copy(struct gnet_dump *d, int
 	return 0;
 
 nla_put_failure:
+	kfree(d->xstats);
+	d->xstats = NULL;
+	d->xstats_len = 0;
 	spin_unlock_bh(d->lock);
 	return -1;
 }
@@ -204,7 +207,9 @@ int
 gnet_stats_copy_app(struct gnet_dump *d, void *st, int len)
 {
 	if (d->compat_xstats) {
-		d->xstats = st;
+		d->xstats = kmemdup(st, len, GFP_ATOMIC);
+		if (!d->xstats)
+			goto err_out;
 		d->xstats_len = len;
 	}
 
@@ -212,6 +217,11 @@ gnet_stats_copy_app(struct gnet_dump *d,
 		return gnet_stats_copy(d, TCA_STATS_APP, st, len);
 
 	return 0;
+
+err_out:
+	d->xstats_len = 0;
+	spin_unlock_bh(d->lock);
+	return -1;
 }
 EXPORT_SYMBOL(gnet_stats_copy_app);
 
@@ -244,6 +254,9 @@ gnet_stats_finish_copy(struct gnet_dump
 			return -1;
 	}
 
+	kfree(d->xstats);
+	d->xstats = NULL;
+	d->xstats_len = 0;
 	spin_unlock_bh(d->lock);
 	return 0;
 }

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