[PATCH net 2/2] net: atm: fix /proc/net/atm/lec handling

[Eric Dumazet <edumazet@google.com>]

/proc/net/atm/lec must ensure safety against dev_lec[] changes.

It appears it had dev_put() calls without prior dev_hold(),
leading to imbalance and UAF.

Fixes: da177e4c3f41 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/atm/lec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/atm/lec.c b/net/atm/lec.c
index 1e1f3eb0e2ba3cc1caa52e49327cecb8d18250e7..afb8d3eb2185078eb994e70c67d581e6dd96a452 100644
--- a/net/atm/lec.c
+++ b/net/atm/lec.c
@@ -909,7 +909,6 @@ static void *lec_itf_walk(struct lec_state *state, loff_t *l)
 	v = (dev && netdev_priv(dev)) ?
 		lec_priv_walk(state, l, netdev_priv(dev)) : NULL;
 	if (!v && dev) {
-		dev_put(dev);
 		/* Partial state reset for the next time we get called */
 		dev = NULL;
 	}
@@ -933,6 +932,7 @@ static void *lec_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	struct lec_state *state = seq->private;
 
+	mutex_lock(&lec_mutex);
 	state->itf = 0;
 	state->dev = NULL;
 	state->locked = NULL;
@@ -950,8 +950,9 @@ static void lec_seq_stop(struct seq_file *seq, void *v)
 	if (state->dev) {
 		spin_unlock_irqrestore(&state->locked->lec_arp_lock,
 				       state->flags);
-		dev_put(state->dev);
+		state->dev = NULL;
 	}
+	mutex_unlock(&lec_mutex);
 }
 
 static void *lec_seq_next(struct seq_file *seq, void *v, loff_t *pos)
-- 
2.50.0.rc2.696.g1fc2a0284f-goog