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Message-Id:
<20250407-bound-checking-ppp_txmung-v1-1-cfcd2efe39e3@arnaud-lcm.com>
Date: Mon, 07 Apr 2025 17:26:21 +0200
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: linux-ppp@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, contact@...aud-lcm.com,
skhan@...uxfoundation.org,
syzbot+29fc8991b0ecb186cf40@...kaller.appspotmail.com
Subject: [PATCH] net: ppp: Add bound checking for skb d on ppp_sync_txmung
Ensure we have enough data in linear buffer from skb before accessing
initial bytes. This prevents potential out-of-bounds accesses
when processing short packets.
When ppp_sync_txmung receives an incoming package with an empty
payload:
(remote) gef⤠p *(struct pppoe_hdr *) (skb->head + skb->network_header)
$18 = {
type = 0x1,
ver = 0x1,
code = 0x0,
sid = 0x2,
length = 0x0,
tag = 0xffff8880371cdb96
}
from the skb struct (trimmed)
tail = 0x16,
end = 0x140,
head = 0xffff88803346f400 "4",
data = 0xffff88803346f416 ":\377",
truesize = 0x380,
len = 0x0,
data_len = 0x0,
mac_len = 0xe,
hdr_len = 0x0,
it is not safe to access data[2].
Reported-by: syzbot+29fc8991b0ecb186cf40@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40
Tested-by: syzbot+29fc8991b0ecb186cf40@...kaller.appspotmail.com
Fixes: 9946eaf552b1 ("Merge tag 'hardening-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux")
Signed-off-by: Arnaud Lecomte <contact@...aud-lcm.com>
---
drivers/net/ppp/ppp_synctty.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c
index 644e99fc3623..520d895acc60 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -506,6 +506,11 @@ ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
unsigned char *data;
int islcp;
+ /* Ensure we can safely access protocol field and LCP code */
+ if (!skb || !pskb_may_pull(skb, 3)) {
+ kfree_skb(skb);
+ return NULL;
+ }
data = skb->data;
proto = get_unaligned_be16(data);
---
base-commit: 9946eaf552b194bb352c2945b54ff98c8193b3f1
change-id: 20250405-bound-checking-ppp_txmung-4807c854ed85
Best regards,
--
Arnaud Lecomte <contact@...aud-lcm.com>
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