From edffc2178d4ba10a61e150b42ef5e7d797714eb3 Mon Sep 17 00:00:00 2001 From: Guillaume Nault Date: Fri, 26 Feb 2016 18:45:34 +0100 Subject: [PATCH] ppp: lock ppp->flags in ppp_read() and ppp_poll() ppp_read() and ppp_poll() can be called concurrently with ppp_ioctl(). In this case, ppp_ioctl() might call ppp_ccp_closed(), which may update ppp->flags while ppp_read() or ppp_poll() is reading it. The update done by ppp_ccp_closed() isn't atomic due to the bit mask operation ('ppp->flags &= ~(SC_CCP_OPEN | SC_CCP_UP)'), so concurrent readers might get transient values. Reading incorrect ppp->flags may disturb the 'ppp->flags & SC_LOOP_TRAFFIC' test in ppp_read() and ppp_poll(), which in turn can lead to improper decision on whether the PPP unit file is ready for reading or not. Since ppp_ccp_closed() is protected by the Rx and Tx locks (with ppp_lock()), taking the Rx lock is enough for ppp_read() and ppp_poll() to guarantee that ppp_ccp_closed() won't update ppp->flags concurrently. The same reasoning applies to ppp->n_channels. The 'n_channels' field can also be written to concurrently by ppp_ioctl() (through ppp_connect_channel() or ppp_disconnect_channel()). These writes aren't atomic (simple increment/decrement), but are protected by both the Rx and Tx locks (like in the ppp->flags case). So holding the Rx lock before reading ppp->n_channels also prevents concurrent writes. Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller --- drivers/net/ppp/ppp_generic.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index fc8ad001bc94..e8a5936289c5 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -443,9 +443,14 @@ static ssize_t ppp_read(struct file *file, char __user *buf, * network traffic (demand mode). */ struct ppp *ppp = PF_TO_PPP(pf); + + ppp_recv_lock(ppp); if (ppp->n_channels == 0 && - (ppp->flags & SC_LOOP_TRAFFIC) == 0) + (ppp->flags & SC_LOOP_TRAFFIC) == 0) { + ppp_recv_unlock(ppp); break; + } + ppp_recv_unlock(ppp); } ret = -EAGAIN; if (file->f_flags & O_NONBLOCK) @@ -532,9 +537,12 @@ static unsigned int ppp_poll(struct file *file, poll_table *wait) else if (pf->kind == INTERFACE) { /* see comment in ppp_read */ struct ppp *ppp = PF_TO_PPP(pf); + + ppp_recv_lock(ppp); if (ppp->n_channels == 0 && (ppp->flags & SC_LOOP_TRAFFIC) == 0) mask |= POLLIN | POLLRDNORM; + ppp_recv_unlock(ppp); } return mask; -- 2.34.1