| Message ID | 20230803185947.2379988-1-andrew.kanner@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 59eeb232940515590de513b997539ef495faca9a |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v5,1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit | expand |
Hello: This series was applied to netdev/net.git (main) by Jakub Kicinski <kuba@kernel.org>: On Thu, 3 Aug 2023 20:59:48 +0200 you wrote: > Using the syzkaller repro with reduced packet size it was discovered > that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(), > although pad may be incremented in tun_build_skb(). This may end up > with exceeding the PAGE_SIZE limit in tun_build_skb(). > > Jason Wang <jasowang@redhat.com> proposed to count XDP_PACKET_HEADROOM > always (e.g. without rcu_access_pointer(tun->xdp_prog)) in > tun_can_build_skb() since there's a window during which XDP program > might be attached between tun_can_build_skb() and tun_build_skb(). > > [...] Here is the summary with links: - [net-next,v5,1/2] drivers: net: prevent tun_build_skb() to exceed the packet size limit https://git.kernel.org/netdev/net/c/59eeb2329405 - [net-next,v5,2/2] net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail() https://git.kernel.org/netdev/net/c/d14eea09edf4 You are awesome, thank you!
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 25f0191df00b..100339bc8b04 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1594,7 +1594,7 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile, if (zerocopy) return false; - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) + + if (SKB_DATA_ALIGN(len + TUN_RX_PAD + XDP_PACKET_HEADROOM) + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE) return false;
Using the syzkaller repro with reduced packet size it was discovered that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(), although pad may be incremented in tun_build_skb(). This may end up with exceeding the PAGE_SIZE limit in tun_build_skb(). Jason Wang <jasowang@redhat.com> proposed to count XDP_PACKET_HEADROOM always (e.g. without rcu_access_pointer(tun->xdp_prog)) in tun_can_build_skb() since there's a window during which XDP program might be attached between tun_can_build_skb() and tun_build_skb(). Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set") Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com> --- Notes (akanner): v5: - always count XDP_PACKET_HEADROOM in tun_can_build_skb() as there's a window between tun_can_build_skb() and tun_build_skb() and XDP program might be attached there. - rcu_read_lock/unlock() for tun->xdp_prog were completely removed and there's no need to use rcu_access_pointer() instead which was noted by David Ahern <dsahern@gmail.com>. v4: https://lore.kernel.org/all/20230801220710.464-1-andrew.kanner@gmail.com/T/ - fall back to v1, fixing only missing XDP_PACKET_HEADROOM in pad and removing bpf_xdp_adjust_tail() check for frame_sz. - added rcu read lock, noted by Jason Wang <jasowang@redhat.com> in v1 - I decided to leave the packet length check in tun_can_build_skb() instead of moving to tun_build_skb() suggested by Jason Wang <jasowang@redhat.com>. Otherwise extra packets will be dropped without falling back to tun_alloc_skb(). And in the discussion of v3 Jesper Dangaard Brouer <jbrouer@redhat.com> noticed that XDP is ok with a higher order pages if it's a contiguous physical memory allocation, so falling to tun_alloc_skb() -> do_xdp_generic() should be ok. v3: https://lore.kernel.org/all/20230725155403.796-1-andrew.kanner@gmail.com/T/ - attach the forgotten changelog v2: https://lore.kernel.org/all/20230725153941.653-1-andrew.kanner@gmail.com/T/ - merged 2 patches in 1, fixing both issues: WARN_ON_ONCE with syzkaller repro and missing XDP_PACKET_HEADROOM in pad - changed the title and description of the execution path, suggested by Jason Wang <jasowang@redhat.com> - move the limit check from tun_can_build_skb() to tun_build_skb() to remove duplication and locking issue, and also drop the packet in case of a failed check - noted by Jason Wang <jasowang@redhat.com> v1: https://lore.kernel.org/all/20230724221326.384-1-andrew.kanner@gmail.com/T/ drivers/net/tun.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)