0b7959b625
BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1
Call Trace:
? napi_gro_frags+0xa7/0x2c0
tun_get_user+0xb50/0xf20
tun_chr_write_iter+0x53/0x70
new_sync_write+0xff/0x160
vfs_write+0x191/0x1e0
__x64_sys_write+0x5e/0xd0
do_syscall_64+0x47/0xf0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
I think there is a subtle race between sending a packet via tap and
attaching it:
CPU0: CPU1:
tun_chr_ioctl(TUNSETIFF)
tun_set_iff
tun_attach
rcu_assign_pointer(tfile->tun, tun);
tun_fops->write_iter()
tun_chr_write_iter
tun_napi_alloc_frags
napi_get_frags
napi->skb = napi_alloc_skb
tun_napi_init
netif_napi_add
napi->skb = NULL
napi->skb is NULL here
napi_gro_frags
napi_frags_skb
skb = napi->skb
skb_reset_mac_header(skb)
panic()
Move rcu_assign_pointer(tfile->tun) and rcu_assign_pointer(tun->tfiles) to
be the last thing we do in tun_attach(); this should guarantee that when we
call tun_get() we always get an initialized object.
v2 changes:
* remove extra napi_mutex locks/unlocks for napi operations
Reported-by: syzbot <syzkaller@googlegroups.com>
Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Stanislav Fomichev <sdf@google.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.