| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-26804: net: ip_tunnel: prevent perpetual headroom growth |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| net: ip_tunnel: prevent perpetual headroom growth |
| |
| syzkaller triggered following kasan splat: |
| BUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 |
| Read of size 1 at addr ffff88812fb4000e by task syz-executor183/5191 |
| [..] |
| kasan_report+0xda/0x110 mm/kasan/report.c:588 |
| __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 |
| skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline] |
| ___skb_get_hash net/core/flow_dissector.c:1791 [inline] |
| __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856 |
| skb_get_hash include/linux/skbuff.h:1556 [inline] |
| ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748 |
| ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308 |
| __netdev_start_xmit include/linux/netdevice.h:4940 [inline] |
| netdev_start_xmit include/linux/netdevice.h:4954 [inline] |
| xmit_one net/core/dev.c:3548 [inline] |
| dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 |
| __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349 |
| dev_queue_xmit include/linux/netdevice.h:3134 [inline] |
| neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592 |
| ... |
| ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235 |
| ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 |
| .. |
| iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 |
| ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831 |
| ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665 |
| __netdev_start_xmit include/linux/netdevice.h:4940 [inline] |
| netdev_start_xmit include/linux/netdevice.h:4954 [inline] |
| xmit_one net/core/dev.c:3548 [inline] |
| dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 |
| ... |
| |
| The splat occurs because skb->data points past skb->head allocated area. |
| This is because neigh layer does: |
| __skb_pull(skb, skb_network_offset(skb)); |
| |
| ... but skb_network_offset() returns a negative offset and __skb_pull() |
| arg is unsigned. IOW, we skb->data gets "adjusted" by a huge value. |
| |
| The negative value is returned because skb->head and skb->data distance is |
| more than 64k and skb->network_header (u16) has wrapped around. |
| |
| The bug is in the ip_tunnel infrastructure, which can cause |
| dev->needed_headroom to increment ad infinitum. |
| |
| The syzkaller reproducer consists of packets getting routed via a gre |
| tunnel, and route of gre encapsulated packets pointing at another (ipip) |
| tunnel. The ipip encapsulation finds gre0 as next output device. |
| |
| This results in the following pattern: |
| |
| 1). First packet is to be sent out via gre0. |
| Route lookup found an output device, ipip0. |
| |
| 2). |
| ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future |
| output device, rt.dev->needed_headroom (ipip0). |
| |
| 3). |
| ip output / start_xmit moves skb on to ipip0. which runs the same |
| code path again (xmit recursion). |
| |
| 4). |
| Routing step for the post-gre0-encap packet finds gre0 as output device |
| to use for ipip0 encapsulated packet. |
| |
| tunl0->needed_headroom is then incremented based on the (already bumped) |
| gre0 device headroom. |
| |
| This repeats for every future packet: |
| |
| gre0->needed_headroom gets inflated because previous packets' ipip0 step |
| incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 |
| needed_headroom was increased. |
| |
| For each subsequent packet, gre/ipip0->needed_headroom grows until |
| post-expand-head reallocations result in a skb->head/data distance of |
| more than 64k. |
| |
| Once that happens, skb->network_header (u16) wraps around when |
| pskb_expand_head tries to make sure that skb_network_offset() is unchanged |
| after the headroom expansion/reallocation. |
| |
| After this skb_network_offset(skb) returns a different (and negative) |
| result post headroom expansion. |
| |
| The next trip to neigh layer (or anything else that would __skb_pull the |
| network header) makes skb->data point to a memory location outside |
| skb->head area. |
| |
| v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to |
| prevent perpetual increase instead of dropping the headroom increment |
| completely. |
| |
| The Linux kernel CVE team has assigned CVE-2024-26804 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 5.4.271 with commit f81e94d2dcd2397137edcb8b85f4c5bed5d22383 |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 5.10.212 with commit 2e95350fe9db9d53c701075060ac8ac883b68aee |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 5.15.151 with commit afec0c5cd2ed71ca95a8b36a5e6d03333bf34282 |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 6.1.81 with commit ab63de24ebea36fe73ac7121738595d704b66d96 |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 6.6.21 with commit a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9 |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 6.7.9 with commit 049d7989c67e8dd50f07a2096dbafdb41331fb9b |
| Issue introduced in 2.6.34 with commit 243aad830e8a4cdda261626fbaeddde16b08d04a and fixed in 6.8 with commit 5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f |
| Issue introduced in 2.6.33.2 with commit 03017375b0122453e6dda833ff7bd4191915def5 |
| |
| 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-2024-26804 |
| 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: |
| net/ipv4/ip_tunnel.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/f81e94d2dcd2397137edcb8b85f4c5bed5d22383 |
| https://git.kernel.org/stable/c/2e95350fe9db9d53c701075060ac8ac883b68aee |
| https://git.kernel.org/stable/c/afec0c5cd2ed71ca95a8b36a5e6d03333bf34282 |
| https://git.kernel.org/stable/c/ab63de24ebea36fe73ac7121738595d704b66d96 |
| https://git.kernel.org/stable/c/a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9 |
| https://git.kernel.org/stable/c/049d7989c67e8dd50f07a2096dbafdb41331fb9b |
| https://git.kernel.org/stable/c/5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f |
