In pppol2tp_proc_open() and l2tp_dfs_seq_open(), iteration state (pd->tunnel and pd->session) is kept in seq_file private data to allow iteration across multiple read() system calls. However, if userspace closes /proc/net/pppol2tp or /sys/kernel/debug/l2tp/tunnels before reading to end-of-file (EOF), any tunnel or session reference stored in pd->tunnel / pd->session is left un-dropped when seq_file private data is freed. Fix this by dropping any remaining pd->tunnel and pd->session references in pppol2tp_proc_release() and l2tp_dfs_seq_release() when closing the file. 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") Reported-by: syzbot+d6fa74e3f19d6ee01e3a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a760f32.01d0871a.3a0d52.004f.GAE@google.com/T/#u Assisted-by: Jetski:Gemini-3.1-Pro Cc: James Chapman Cc: Guillaume Nault Signed-off-by: Eric Dumazet --- v3: fix CONFIG_PROC_FS=n case (Paolo) v2: https://lore.kernel.org/netdev/20260810141125.1176545-1-edumazet@google.com/ net/l2tp/l2tp_debugfs.c | 4 +++ net/l2tp/l2tp_ppp.c | 56 ++++++++++++++++++++++++++++++++++++++--- 2 files changed, 57 insertions(+), 3 deletions(-) diff --git a/net/l2tp/l2tp_debugfs.c b/net/l2tp/l2tp_debugfs.c index b26986fda9d6cf096519d56032fe3deb5034c7c8..c12d5e1ee550ccc2608b6128cb653ca373280373 100644 --- a/net/l2tp/l2tp_debugfs.c +++ b/net/l2tp/l2tp_debugfs.c @@ -306,6 +306,10 @@ static int l2tp_dfs_seq_release(struct inode *inode, struct file *file) seq = file->private_data; pd = seq->private; + if (pd->session) + l2tp_session_put(pd->session); + if (pd->tunnel) + l2tp_tunnel_put(pd->tunnel); if (pd->net) put_net_track(pd->net, &pd->ns_tracker); kfree(pd); diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index f8881699e1cad88e6f312e6ca47ae0af94c6137c..ef8fdfaf051d4602691fbd82e164e3b1eb31a86b 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -1597,7 +1597,53 @@ static const struct seq_operations pppol2tp_seq_ops = { .stop = pppol2tp_seq_stop, .show = pppol2tp_seq_show, }; -#endif /* CONFIG_PROC_FS */ + +static int pppol2tp_proc_open(struct inode *inode, struct file *file) +{ + struct net *net = pde_data(inode); + struct pppol2tp_seq_data *pd; + + net = maybe_get_net(net); + if (!net) + return -ENXIO; + + pd = __seq_open_private(file, &pppol2tp_seq_ops, sizeof(*pd)); + if (!pd) { + put_net(net); + return -ENOMEM; + } + +#ifdef CONFIG_NET_NS + pd->p.net = net; + netns_tracker_alloc(net, &pd->p.ns_tracker, GFP_KERNEL); +#endif + return 0; +} + +static int pppol2tp_proc_release(struct inode *inode, struct file *file) +{ + struct seq_file *seq = file->private_data; + struct pppol2tp_seq_data *pd = seq->private; + + if (pd->session) + l2tp_session_put(pd->session); + if (pd->tunnel) + l2tp_tunnel_put(pd->tunnel); + +#ifdef CONFIG_NET_NS + put_net_track(pd->p.net, &pd->p.ns_tracker); +#else + put_net(&init_net); +#endif + return seq_release_private(inode, file); +} + +static const struct proc_ops pppol2tp_proc_ops = { + .proc_open = pppol2tp_proc_open, + .proc_read = seq_read, + .proc_lseek = seq_lseek, + .proc_release = pppol2tp_proc_release, +}; /***************************************************************************** * Network namespace @@ -1608,8 +1654,8 @@ static __net_init int pppol2tp_init_net(struct net *net) struct proc_dir_entry *pde; int err = 0; - pde = proc_create_net("pppol2tp", 0444, net->proc_net, - &pppol2tp_seq_ops, sizeof(struct pppol2tp_seq_data)); + pde = proc_create_data("pppol2tp", 0444, net->proc_net, + &pppol2tp_proc_ops, net); if (!pde) { err = -ENOMEM; goto out; @@ -1624,9 +1670,13 @@ static __net_exit void pppol2tp_exit_net(struct net *net) remove_proc_entry("pppol2tp", net->proc_net); } +#endif /* CONFIG_PROC_FS */ + static struct pernet_operations pppol2tp_net_ops = { +#ifdef CONFIG_PROC_FS .init = pppol2tp_init_net, .exit = pppol2tp_exit_net, +#endif }; /***************************************************************************** -- 2.55.0.679.g6767b8d81c-goog