4e4b08e558
In tun.c skb->len was accessed while doing stats accounting after a call to netif_receive_skb. We can not access skb after this call because buffers may be dropped. The fix for this bug would be to store skb->len in local variable and then use it after netif_receive_skb(). IMO using xdp data size for accounting bytes will be better because input for tun_xdp_one() is xdp_buff. Hence this patch: - fixes a bug by removing skb access after netif_receive_skb() - uses xdp data size for accounting bytes [613.019057] BUG: KASAN: use-after-free in tun_sendmsg+0x77c/0xc50 [tun] [613.021062] Read of size 4 at addr ffff8881da9ab7c0 by task vhost-1115/1155 [613.023073] [613.024003] CPU: 0 PID: 1155 Comm: vhost-1115 Not tainted 4.20.0-rc3-vm+ #232 [613.026029] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [613.029116] Call Trace: [613.031145] dump_stack+0x5b/0x90 [613.032219] print_address_description+0x6c/0x23c [613.034156] ? tun_sendmsg+0x77c/0xc50 [tun] [613.036141] kasan_report.cold.5+0x241/0x308 [613.038125] tun_sendmsg+0x77c/0xc50 [tun] [613.040109] ? tun_get_user+0x1960/0x1960 [tun] [613.042094] ? __isolate_free_page+0x270/0x270 [613.045173] vhost_tx_batch.isra.14+0xeb/0x1f0 [vhost_net] [613.047127] ? peek_head_len.part.13+0x90/0x90 [vhost_net] [613.049096] ? get_tx_bufs+0x5a/0x2c0 [vhost_net] [613.051106] ? vhost_enable_notify+0x2d8/0x420 [vhost] [613.053139] handle_tx_copy+0x2d0/0x8f0 [vhost_net] [613.053139] ? vhost_net_buf_peek+0x340/0x340 [vhost_net] [613.053139] ? __mutex_lock+0x8d9/0xb30 [613.053139] ? finish_task_switch+0x8f/0x3f0 [613.053139] ? handle_tx+0x32/0x120 [vhost_net] [613.053139] ? mutex_trylock+0x110/0x110 [613.053139] ? finish_task_switch+0xcf/0x3f0 [613.053139] ? finish_task_switch+0x240/0x3f0 [613.053139] ? __switch_to_asm+0x34/0x70 [613.053139] ? __switch_to_asm+0x40/0x70 [613.053139] ? __schedule+0x506/0xf10 [613.053139] handle_tx+0xc7/0x120 [vhost_net] [613.053139] vhost_worker+0x166/0x200 [vhost] [613.053139] ? vhost_dev_init+0x580/0x580 [vhost] [613.053139] ? __kthread_parkme+0x77/0x90 [613.053139] ? vhost_dev_init+0x580/0x580 [vhost] [613.053139] kthread+0x1b1/0x1d0 [613.053139] ? kthread_park+0xb0/0xb0 [613.053139] ret_from_fork+0x35/0x40 [613.088705] [613.088705] Allocated by task 1155: [613.088705] kasan_kmalloc+0xbf/0xe0 [613.088705] kmem_cache_alloc+0xdc/0x220 [613.088705] __build_skb+0x2a/0x160 [613.088705] build_skb+0x14/0xc0 [613.088705] tun_sendmsg+0x4f0/0xc50 [tun] [613.088705] vhost_tx_batch.isra.14+0xeb/0x1f0 [vhost_net] [613.088705] handle_tx_copy+0x2d0/0x8f0 [vhost_net] [613.088705] handle_tx+0xc7/0x120 [vhost_net] [613.088705] vhost_worker+0x166/0x200 [vhost] [613.088705] kthread+0x1b1/0x1d0 [613.088705] ret_from_fork+0x35/0x40 [613.088705] [613.088705] Freed by task 1155: [613.088705] __kasan_slab_free+0x12e/0x180 [613.088705] kmem_cache_free+0xa0/0x230 [613.088705] ip6_mc_input+0x40f/0x5a0 [613.088705] ipv6_rcv+0xc9/0x1e0 [613.088705] __netif_receive_skb_one_core+0xc1/0x100 [613.088705] netif_receive_skb_internal+0xc4/0x270 [613.088705] br_pass_frame_up+0x2b9/0x2e0 [613.088705] br_handle_frame_finish+0x2fb/0x7a0 [613.088705] br_handle_frame+0x30f/0x6c0 [613.088705] __netif_receive_skb_core+0x61a/0x15b0 [613.088705] __netif_receive_skb_one_core+0x8e/0x100 [613.088705] netif_receive_skb_internal+0xc4/0x270 [613.088705] tun_sendmsg+0x738/0xc50 [tun] [613.088705] vhost_tx_batch.isra.14+0xeb/0x1f0 [vhost_net] [613.088705] handle_tx_copy+0x2d0/0x8f0 [vhost_net] [613.088705] handle_tx+0xc7/0x120 [vhost_net] [613.088705] vhost_worker+0x166/0x200 [vhost] [613.088705] kthread+0x1b1/0x1d0 [613.088705] ret_from_fork+0x35/0x40 [613.088705] [613.088705] The buggy address belongs to the object at ffff8881da9ab740 [613.088705] which belongs to the cache skbuff_head_cache of size 232 Fixes: 043d222f93ab ("tuntap: accept an array of XDP buffs through sendmsg()") Reviewed-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp> Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp> Acked-by: Jason Wang <jasowang@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.