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([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a359fc1207sm4434875e9.1.2026.10.23.12.53.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 12:53:11 -0700 (PDT) From: Tristan Madani To: Andrew Lunn , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Qingfang Deng , linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tristan Madani Subject: [PATCH net] ppp: fix stale pointer access after pskb_may_pull in ppp_ccp_peek Date: Fri, 23 Oct 2026 19:53:09 +0000 Message-ID: <20261023195309.3527129-1-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 X-Mailing-List: linux-ppp@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani ppp_ccp_peek() caches a pointer to skb->data in dp after the first pskb_may_pull(), then uses dp after a second pskb_may_pull(skb, len + 2) in the CCP_CONFACK handler. If the second pull triggers pskb_expand_head() due to a cloned skb or frag linearization, skb->head is freed and reallocated, leaving dp stale. The stale dp is subsequently used in CCP_OPT_LENGTH() and passed to decomp_init()/comp_init() which read from the freed memory. Re-derive dp from skb->data after the second pskb_may_pull. Fixes: 1da177e4c3f41 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- drivers/net/ppp/ppp_generic.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 1a610a18893ba..3998ce4332f42 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -3157,6 +3157,7 @@ ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound) len = CCP_LENGTH(dp); if (!pskb_may_pull(skb, len + 2)) return; /* too short */ + dp = skb->data + 2; dp += CCP_HDRLEN; len -= CCP_HDRLEN; if (len < CCP_OPT_MINLEN || len < CCP_OPT_LENGTH(dp)) -- 2.47.3