| Message ID | 20190107213839.83297-1-sdf@google.com |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net,v2,1/2] tun: publish tfile after it's fully initialized | expand |
From: Stanislav Fomichev <sdf@google.com> Date: Mon, 7 Jan 2019 13:38:38 -0800 > BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 > Call Trace: ... > > I think there is a subtle race between sending a packet via tap and > attaching it: > > CPU0: CPU1: > tun_chr_ioctl(TUNSETIFF) ... > 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> Applied and queued up for -stable. Please, the next time you submit a patch series, provide a proper header posting. Thank you.
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index a4fdad475594..18656c4094b3 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -856,10 +856,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, err = 0; } - rcu_assign_pointer(tfile->tun, tun); - rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); - tun->numqueues++; - if (tfile->detached) { tun_enable_queue(tfile); } else { @@ -876,6 +872,13 @@ static int tun_attach(struct tun_struct *tun, struct file *file, * refcnt. */ + /* Publish tfile->tun and tun->tfiles only after we've fully + * initialized tfile; otherwise we risk using half-initialized + * object. + */ + rcu_assign_pointer(tfile->tun, tun); + rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); + tun->numqueues++; out: return err; }
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> --- drivers/net/tun.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)