6.6-stable review patch. If anyone has any objections, please let me know.
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From: Qingfang Deng dqfext@gmail.com
[ Upstream commit 0417adf367a0af11adf7ace849af4638cfb573f7 ]
ppp_fill_forward_path() has two race conditions:
1. The ppp->channels list can change between list_empty() and list_first_entry(), as ppp_lock() is not held. If the only channel is deleted in ppp_disconnect_channel(), list_first_entry() may access an empty head or a freed entry, and trigger a panic.
2. pch->chan can be NULL. When ppp_unregister_channel() is called, pch->chan is set to NULL before pch is removed from ppp->channels.
Fix these by using a lockless RCU approach: - Use list_first_or_null_rcu() to safely test and access the first list entry. - Convert list modifications on ppp->channels to their RCU variants and add synchronize_net() after removal. - Check for a NULL pch->chan before dereferencing it.
Fixes: f6efc675c9dd ("net: ppp: resolve forwarding path for bridge pppoe devices") Signed-off-by: Qingfang Deng dqfext@gmail.com Link: https://patch.msgid.link/20250814012559.3705-2-dqfext@gmail.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ppp/ppp_generic.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index ee1527cf3d0c..28b894bcd7a9 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -33,6 +33,7 @@ #include <linux/ppp_channel.h> #include <linux/ppp-comp.h> #include <linux/skbuff.h> +#include <linux/rculist.h> #include <linux/rtnetlink.h> #include <linux/if_arp.h> #include <linux/ip.h> @@ -1613,11 +1614,14 @@ static int ppp_fill_forward_path(struct net_device_path_ctx *ctx, if (ppp->flags & SC_MULTILINK) return -EOPNOTSUPP;
- if (list_empty(&ppp->channels)) + pch = list_first_or_null_rcu(&ppp->channels, struct channel, clist); + if (!pch) + return -ENODEV; + + chan = READ_ONCE(pch->chan); + if (!chan) return -ENODEV;
- pch = list_first_entry(&ppp->channels, struct channel, clist); - chan = pch->chan; if (!chan->ops->fill_forward_path) return -EOPNOTSUPP;
@@ -3000,7 +3004,7 @@ ppp_unregister_channel(struct ppp_channel *chan) */ down_write(&pch->chan_sem); spin_lock_bh(&pch->downl); - pch->chan = NULL; + WRITE_ONCE(pch->chan, NULL); spin_unlock_bh(&pch->downl); up_write(&pch->chan_sem); ppp_disconnect_channel(pch); @@ -3506,7 +3510,7 @@ ppp_connect_channel(struct channel *pch, int unit) hdrlen = pch->file.hdrlen + 2; /* for protocol bytes */ if (hdrlen > ppp->dev->hard_header_len) ppp->dev->hard_header_len = hdrlen; - list_add_tail(&pch->clist, &ppp->channels); + list_add_tail_rcu(&pch->clist, &ppp->channels); ++ppp->n_channels; pch->ppp = ppp; refcount_inc(&ppp->file.refcnt); @@ -3536,10 +3540,11 @@ ppp_disconnect_channel(struct channel *pch) if (ppp) { /* remove it from the ppp unit's list */ ppp_lock(ppp); - list_del(&pch->clist); + list_del_rcu(&pch->clist); if (--ppp->n_channels == 0) wake_up_interruptible(&ppp->file.rwait); ppp_unlock(ppp); + synchronize_net(); if (refcount_dec_and_test(&ppp->file.refcnt)) ppp_destroy_interface(ppp); err = 0;