From: Lee Jones <lee@kernel.org> mainline inclusion from mainline-v7.1-rc7 commit a213a8950414c684999dcf03edeea6c46ede172e category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15948 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- pppol2tp_ioctl() read sock->sk->sk_user_data directly without any locks or reference counting. If a controllable sleep was induced during copy_from_user() (e.g. via a userfaultfd page fault sleep), a concurrent socket close could trigger pppol2tp_session_close() asynchronously. This frees the l2tp_session structure via the l2tp_session_del_work workqueue. Upon resuming, the ioctl thread dereferences the stale session pointer, resulting in a Use-After-Free (UAF). Fix this by securely fetching the session reference using the RCU-safe, refcounted helper pppol2tp_sock_to_session(sk) on entry. This locks the session's refcount across the sleep. We structured the function to exit via standard err breaks, guaranteeing that l2tp_session_put() is cleanly called on all return paths to drop the reference. To preserve existing behavior we validate the session and its magic signature only for the specific L2TP commands that require it. This ensures that generic/unknown ioctls called on an unconnected socket still return -ENOIOCTLCMD and correctly fall back to generic handlers (e.g. in sock_do_ioctl()). Signed-off-by: Lee Jones <lee@kernel.org> Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Link: https://patch.msgid.link/20260527133630.2120612-1-lee@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org> Conflicts: net/l2tp/l2tp_ppp.c [Function l2tp_session_put() conflicts due to mainline commit abe7a1a7d0b6 ("l2tp: improve tunnel/session refcount helpers") and commit c5cbaef992d64 ("l2tp: refactor ppp socket/session relationship") not merge.] Signed-off-by: Gu Bowen <gubowen5@huawei.com> --- net/l2tp/l2tp_ppp.c | 82 +++++++++++++++++++++++++++------------------ 1 file changed, 50 insertions(+), 32 deletions(-) diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index 7ee095e854ae..de10e7783334 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -1055,64 +1055,76 @@ static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd, { struct pppol2tp_ioc_stats stats; struct l2tp_session *session; + int err = 0; + + session = pppol2tp_sock_to_session(sock->sk); + /* Validate session presence and magic integrity ONLY for commands + * that belong to L2TP and require a valid session. + */ switch (cmd) { case PPPIOCGMRU: case PPPIOCGFLAGS: - session = sock->sk->sk_user_data; + case PPPIOCSMRU: + case PPPIOCSFLAGS: + case PPPIOCGL2TPSTATS: if (!session) return -ENOTCONN; - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) + if (session->magic != L2TP_SESSION_MAGIC) { + sock_put(sock->sk); return -EBADF; + } + break; + default: + break; + } + switch (cmd) { + case PPPIOCGMRU: + case PPPIOCGFLAGS: /* Not defined for tunnels */ - if (!session->session_id && !session->peer_session_id) - return -ENOSYS; + if (!session->session_id && !session->peer_session_id) { + err = -ENOSYS; + break; + } - if (put_user(0, (int __user *)arg)) - return -EFAULT; + if (put_user(0, (int __user *)arg)) { + err = -EFAULT; + break; + } break; case PPPIOCSMRU: case PPPIOCSFLAGS: - session = sock->sk->sk_user_data; - if (!session) - return -ENOTCONN; - - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) - return -EBADF; - /* Not defined for tunnels */ - if (!session->session_id && !session->peer_session_id) - return -ENOSYS; + if (!session->session_id && !session->peer_session_id) { + err = -ENOSYS; + break; + } - if (!access_ok((int __user *)arg, sizeof(int))) - return -EFAULT; + if (!access_ok((int __user *)arg, sizeof(int))) { + err = -EFAULT; + break; + } break; case PPPIOCGL2TPSTATS: - session = sock->sk->sk_user_data; - if (!session) - return -ENOTCONN; - - if (WARN_ON(session->magic != L2TP_SESSION_MAGIC)) - return -EBADF; - /* Session 0 represents the parent tunnel */ if (!session->session_id && !session->peer_session_id) { u32 session_id; - int err; if (copy_from_user(&stats, (void __user *)arg, - sizeof(stats))) - return -EFAULT; + sizeof(stats))) { + err = -EFAULT; + break; + } session_id = stats.session_id; err = pppol2tp_tunnel_copy_stats(&stats, session->tunnel); if (err < 0) - return err; + break; stats.session_id = session_id; } else { @@ -1122,15 +1134,21 @@ static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd, stats.tunnel_id = session->tunnel->tunnel_id; stats.using_ipsec = l2tp_tunnel_uses_xfrm(session->tunnel); - if (copy_to_user((void __user *)arg, &stats, sizeof(stats))) - return -EFAULT; + if (copy_to_user((void __user *)arg, &stats, sizeof(stats))) { + err = -EFAULT; + break; + } break; default: - return -ENOIOCTLCMD; + err = -ENOIOCTLCMD; + break; } - return 0; + if (session) + sock_put(sock->sk); + + return err; } /***************************************************************************** -- 2.43.0