From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 908BC49A3D4 for ; Fri, 25 Sep 2026 10:42:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790332942; cv=none; b=XxevQSjZsqKuXv4argrpLREqahkRWSldd3R6/oydYv65UGIO8cLkuDGCqjjYvnAxT1n980TZq7/zKU1th+2URRUts0mrB5Yf0XkC92spl/noyos0oOGI+FEVnzYxia1T8AESDCmA6GbAAzff5AQlCtjbRboDsp6aqFSOBjNEwmQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790332942; c=relaxed/simple; bh=qN7Onounf1IIU2dsuBzZcE2Uku2sn5VTtfJLYb4cEAU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=H+m7B4lrcH2MjObhjiaCV8TP3QPhMgY6m31QP0EJW5SFyWJourQRA6m3f6aw+BqN3G7J89uYVnP+Sz2GuhEXc9C6cH2G8Sj/uGwqxwgW8grVALfcJzbnGaSLOoDQBI06WeCbHa5+Rhl9g1nZsIBxSVGsafvM/geG/ZQBQgTgZzI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wpeSArVx; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wpeSArVx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAEF41F000FF; Fri, 25 Sep 2026 10:42:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790332941; bh=cWEbdOmwSlzAlYrHFosoUyYXy46Wlj4gbGkL0K1Ss5k=; h=From:To:Cc:Subject:Date:Reply-To; b=wpeSArVx9Be+A2T1ZQ3HdyYtDoIBLjLJSzLUP+pfitTpFYoiV8IB0n9pgw33nGfx8 B7QIkNeWMy1UzcEh9nx6ZqJIVtgqrtE7i75ei1s8epn2zqnQ/GxcbX81+LcyPbnY1o Hs3JcMkezLGuJdA8vl+DqntCKjUv3Xqs2RpoPPhQ= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-98158: ppp_async: drop the errored frame instead of resetting its headroom Date: Fri, 25 Sep 2026 12:40:05 +0200 Message-ID: <2026092520-CVE-2026-98158-e9e9@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4688; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=pYnr3t80OkOynDSYrTvVtkC+5AzbFh9/H2vDdvYo9GA=; b=owGbwMvMwCRo6H6F97bub03G02pJDFnb/CMet1W9z3N5c3Lulr0RTc+8Yvxs2w4Xvd1/M8POr tTW8f65jlgWBkEmBlkxRZYv23iO7q84pOhlaHsaZg4rE8gQBi5OAZiIeDTDXOGD27TEVLZbGWQ3 ch2Ydmx3zMxZ/QwLLkou9KhOeOVR8a2Pbco2zevMO9xVAA== X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: ppp_async: drop the errored frame instead of resetting its headroom ppp_receive_nonmp_frame() prepends a two-byte direction tag before running the pass/active BPF filters: *(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG); Nothing on the receive path guarantees those two bytes of headroom. The frame-error path in ppp_async's process_input_packet() resets a reused skb's headroom to zero while claiming to restore it to a freshly allocated state - but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD: err: if (skb) { /* make skb appear as freshly allocated */ skb_trim(skb, 0); skb_reserve(skb, - skb_headroom(skb)); } ap->rpkt still points at that skb, so the next frame is reassembled into it with no headroom at all. A peer that sends a bad-FCS frame followed by one beginning ff 03 then leaves a single byte of headroom by the time the filter tag is pushed, which lands one byte below skb->head: skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000 data:ffff888003c0ffff tail:0x30 end:0x640 dev: kernel BUG at net/core/skbuff.c:214! RIP: 0010:skb_panic+0x13e/0x230 Call Trace: skb_push+0xbd/0x100 ppp_receive_nonmp_frame+0x48a/0x1d10 ppp_input+0x4e9/0x2f80 ppp_async_process+0x2a/0xe0 tasklet_action_common+0x20f/0x8a0 handle_softirqs+0x18e/0x590 Kernel panic - not syncing: Fatal exception in interrupt Zeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb() gives the rest of the receive path. Besides the filter panic above, when CCP compression is enabled ppp_decompress_frame() hands skb->data - 2 to ->decompress()/->incomp(), which then reads out of bounds before skb->head for the same reason. Rather than restore the headroom, drop the errored frame - as ppp_synctty already does on its error path - and clear ap->rpkt so the next frame is reassembled into a fresh skb with proper headroom. This is simpler and fixes both the filter under-panic and the CCP out-of-bounds read. The original V1 of this patch made room in ppp_receive_nonmp_frame() with skb_cow_head(); Eric pointed out that fixing the root cause in the transport is the right approach. Found by fuzzing the PPP receive path with a mutating peer on a pty; it is an interesting (remote) DoS: root configures PPP, the peer supplies two crashing frames. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a second, and returns cleanly with this applied. The Linux kernel CVE team has assigned CVE-2026-98158 to this issue. Affected and fixed versions =========================== Issue introduced in 2.6.15 with commit 6722e78c90054101e6797d5944cdc81af9897a0a and fixed in 6.12.111 with commit d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da Issue introduced in 2.6.15 with commit 6722e78c90054101e6797d5944cdc81af9897a0a and fixed in 6.18.53 with commit 0c53eb14975f029abd6b26896a460f0d2aaefe6b Issue introduced in 2.6.15 with commit 6722e78c90054101e6797d5944cdc81af9897a0a and fixed in 7.2.7 with commit 717137221c7d90e7c98bda9a370c9da6cbf015e5 Issue introduced in 2.6.15 with commit 6722e78c90054101e6797d5944cdc81af9897a0a and fixed in 7.3-rc3 with commit 8dc5d98a16fa23c00999aecf10018c9f69fa5bf4 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-98158 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: drivers/net/ppp/ppp_async.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5 https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4