[PATCH net] ppp: annotate data races in ppp_generic
From: Eric Dumazet <edumazet@google.com>
Date: 2026-07-22 10:16:07
Subsystem:
networking drivers, ppp protocol drivers and compressors, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Several fields in struct ppp can be read or updated concurrently
from multiple CPUs without synchronization, causing data races:
1. ppp->mru is read concurrently in ppp_receive_nonmp_frame() while
being updated via PPPIOCSMRU ioctl. Protect ppp->mru updates in
PPPIOCSMRU with ppp_recv_lock(ppp).
2. PPPIOCGFLAGS reads ppp->flags, ppp->xstate, and ppp->rstate
unlocked. Wrap the read in ppp_lock(ppp) to get a consistent
snapshot.
3. ppp->debug is updated via PPPIOCSDEBUG and read concurrently on
fast paths. Annotate reads with READ_ONCE() and writes with
WRITE_ONCE().
4. ppp->last_xmit and ppp->last_recv are updated on TX/RX data paths
and read via PPPIOCGIDLE32 / PPPIOCGIDLE64 ioctls. Annotate with
WRITE_ONCE() / READ_ONCE() and use max() to handle jiffies
subtraction.
5. ppp->npmode[] is updated via PPPIOCSNPMODE and read on TX/RX
paths. Annotate with WRITE_ONCE() / READ_ONCE().
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
Cc: Qingfang Deng <redacted>
Cc: linux-ppp@vger.kernel.org
---
drivers/net/ppp/ppp_generic.c | 50 ++++++++++++++++++++---------------
1 file changed, 28 insertions(+), 22 deletions(-)
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index ef54e0a0462a175bb989db8dda895e9ae755965f..cacc4c3a37d2cda0aea2e176e5d0638f959e18a3 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c@@ -810,7 +810,9 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) case PPPIOCSMRU: if (get_user(val, p)) break; + ppp_recv_lock(ppp); ppp->mru = val; + ppp_recv_unlock(ppp); err = 0; break;
@@ -831,7 +833,9 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) break; case PPPIOCGFLAGS: + ppp_lock(ppp); val = ppp->flags | ppp->xstate | ppp->rstate; + ppp_unlock(ppp); if (put_user(val, p)) break; err = 0;
@@ -855,7 +859,7 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) case PPPIOCSDEBUG: if (get_user(val, p)) break; - ppp->debug = val; + WRITE_ONCE(ppp->debug, val); err = 0; break;
@@ -866,16 +870,16 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) break; case PPPIOCGIDLE32: - idle32.xmit_idle = (jiffies - ppp->last_xmit) / HZ; - idle32.recv_idle = (jiffies - ppp->last_recv) / HZ; - if (copy_to_user(argp, &idle32, sizeof(idle32))) + idle32.xmit_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_xmit))) / HZ; + idle32.recv_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_recv))) / HZ; + if (copy_to_user(argp, &idle32, sizeof(idle32))) break; err = 0; break; case PPPIOCGIDLE64: - idle64.xmit_idle = (jiffies - ppp->last_xmit) / HZ; - idle64.recv_idle = (jiffies - ppp->last_recv) / HZ; + idle64.xmit_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_xmit))) / HZ; + idle64.recv_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_recv))) / HZ; if (copy_to_user(argp, &idle64, sizeof(idle64))) break; err = 0;
@@ -916,7 +920,7 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) if (copy_to_user(argp, &npi, sizeof(npi))) break; } else { - ppp->npmode[i] = npi.mode; + WRITE_ONCE(ppp->npmode[i], npi.mode); /* we may be able to transmit more packets now (??) */ netif_wake_queue(ppp->dev); }
@@ -1454,7 +1458,7 @@ ppp_start_xmit(struct sk_buff *skb, struct net_device *dev) goto outf; /* Drop, accept or reject the packet */ - switch (ppp->npmode[npi]) { + switch (READ_ONCE(ppp->npmode[npi])) { case NPMODE_PASS: break; case NPMODE_QUEUE:
@@ -1790,7 +1794,7 @@ ppp_prepare_tx_skb(struct ppp *ppp, struct sk_buff **pskb) *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_OUTBOUND_TAG); if (ppp->pass_filter && bpf_prog_run(ppp->pass_filter, skb) == 0) { - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, "PPP: outbound frame " "not passed\n");
@@ -1800,11 +1804,11 @@ ppp_prepare_tx_skb(struct ppp *ppp, struct sk_buff **pskb) /* if this packet passes the active filter, record the time */ if (!(ppp->active_filter && bpf_prog_run(ppp->active_filter, skb) == 0)) - ppp->last_xmit = jiffies; + WRITE_ONCE(ppp->last_xmit, jiffies); skb_pull(skb, 2); #else /* for data packets, record the time */ - ppp->last_xmit = jiffies; + WRITE_ONCE(ppp->last_xmit, jiffies); #endif /* CONFIG_PPP_FILTER */ }
@@ -2154,7 +2158,7 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb) noskb: spin_unlock(&pch->downl); err_linearize: - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_err(ppp->dev, "PPP: no memory (fragment)\n"); DEV_STATS_INC(ppp->dev, tx_errors); ++ppp->nxseq;
@@ -2502,7 +2506,7 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb) *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG); if (ppp->pass_filter && bpf_prog_run(ppp->pass_filter, skb) == 0) { - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, "PPP: inbound frame " "not passed\n");
@@ -2511,14 +2515,14 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb) } if (!(ppp->active_filter && bpf_prog_run(ppp->active_filter, skb) == 0)) - ppp->last_recv = jiffies; + WRITE_ONCE(ppp->last_recv, jiffies); __skb_pull(skb, 2); } else #endif /* CONFIG_PPP_FILTER */ - ppp->last_recv = jiffies; + WRITE_ONCE(ppp->last_recv, jiffies); if ((ppp->dev->flags & IFF_UP) == 0 || - ppp->npmode[npi] != NPMODE_PASS) { + READ_ONCE(ppp->npmode[npi]) != NPMODE_PASS) { kfree_skb(skb); } else { /* chop off protocol */
@@ -2771,7 +2775,7 @@ ppp_mp_reconstruct(struct ppp *ppp) seq = seq_before(minseq, PPP_MP_CB(p)->sequence)? minseq + 1: PPP_MP_CB(p)->sequence; - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, "lost frag %u..%u\n", oldseq, seq-1);
@@ -2820,7 +2824,7 @@ ppp_mp_reconstruct(struct ppp *ppp) struct sk_buff *tmp2; skb_queue_reverse_walk_from_safe(list, p, tmp2) { - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, "discarding frag %u\n", PPP_MP_CB(p)->sequence);
@@ -2842,7 +2846,7 @@ ppp_mp_reconstruct(struct ppp *ppp) skb_queue_walk_safe(list, p, tmp) { if (p == head) break; - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, "discarding frag %u\n", PPP_MP_CB(p)->sequence);
@@ -2850,7 +2854,7 @@ ppp_mp_reconstruct(struct ppp *ppp) kfree_skb(p); } - if (ppp->debug & 1) + if (READ_ONCE(ppp->debug) & 1) netdev_printk(KERN_DEBUG, ppp->dev, " missed pkts %u..%u\n", ppp->nextseq,
@@ -3161,7 +3165,8 @@ ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound) if (!ppp->rc_state) break; if (ppp->rcomp->decomp_init(ppp->rc_state, dp, len, - ppp->file.index, 0, ppp->mru, ppp->debug)) { + ppp->file.index, 0, ppp->mru, + READ_ONCE(ppp->debug))) { ppp->rstate |= SC_DECOMP_RUN; ppp->rstate &= ~(SC_DC_ERROR | SC_DC_FERROR); }
@@ -3170,7 +3175,8 @@ ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound) if (!ppp->xc_state) break; if (ppp->xcomp->comp_init(ppp->xc_state, dp, len, - ppp->file.index, 0, ppp->debug)) + ppp->file.index, 0, + READ_ONCE(ppp->debug))) ppp->xstate |= SC_COMP_RUN; } break;
--
2.55.0.229.g6434b31f56-goog