diff options
| author | Stanislav Fomichev <sdf@google.com> | 2019-01-07 22:38:38 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2019-01-10 15:24:38 +0100 |
| commit | 0b7959b6257322f7693b08a459c505d4938646f2 (patch) | |
| tree | 97b2b16fe998f2a85e29f0fff7449b2c98d5c7bd /drivers/net/tun.c | |
| parent | packet: Do not leak dev refcounts on error exit (diff) | |
| download | linux-0b7959b6257322f7693b08a459c505d4938646f2.tar.xz linux-0b7959b6257322f7693b08a459c505d4938646f2.zip | |
tun: publish tfile after it's fully initialized
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>
Diffstat (limited to 'drivers/net/tun.c')
| -rw-r--r-- | drivers/net/tun.c | 11 |
1 files changed, 7 insertions, 4 deletions
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; } |