4.16-stable review patch. If anyone has any objections, please let me know.
------------------
From: Guillaume Nault g.nault@alphalink.fr
[ Upstream commit 5411b6187adf62909e3b998ac782e722904c7487 ]
Commit 0e0c3fee3a59 ("l2tp: hold reference on tunnels printed in pppol2tp proc file") assumed that if pppol2tp_seq_stop() was called with non-NULL private data (the 'v' pointer), then pppol2tp_seq_start() would not be called again. It turns out that this isn't guaranteed, and overflowing the seq_file's buffer in pppol2tp_seq_show() is a way to get into this situation.
Therefore, pppol2tp_seq_stop() needs to reset pd->tunnel, so that pppol2tp_seq_start() won't drop a reference again if it gets called. We also have to clear pd->session, because the rest of the code expects a non-NULL tunnel when pd->session is set.
The l2tp_debugfs module has the same issue. Fix it in the same way.
Fixes: 0e0c3fee3a59 ("l2tp: hold reference on tunnels printed in pppol2tp proc file") Fixes: f726214d9b23 ("l2tp: hold reference on tunnels printed in l2tp/tunnels debugfs file") Signed-off-by: Guillaume Nault g.nault@alphalink.fr Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/l2tp/l2tp_debugfs.c | 5 ++++- net/l2tp/l2tp_ppp.c | 5 ++++- 2 files changed, 8 insertions(+), 2 deletions(-)
--- a/net/l2tp/l2tp_debugfs.c +++ b/net/l2tp/l2tp_debugfs.c @@ -106,8 +106,11 @@ static void l2tp_dfs_seq_stop(struct seq return;
/* Drop reference taken by last invocation of l2tp_dfs_next_tunnel() */ - if (pd->tunnel) + if (pd->tunnel) { l2tp_tunnel_dec_refcount(pd->tunnel); + pd->tunnel = NULL; + pd->session = NULL; + } }
static void l2tp_dfs_seq_tunnel_show(struct seq_file *m, void *v) --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -1626,8 +1626,11 @@ static void pppol2tp_seq_stop(struct seq return;
/* Drop reference taken by last invocation of pppol2tp_next_tunnel() */ - if (pd->tunnel) + if (pd->tunnel) { l2tp_tunnel_dec_refcount(pd->tunnel); + pd->tunnel = NULL; + pd->session = NULL; + } }
static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)