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Subject[PATCH 5.0 026/146] tun: properly test for IFF_UP
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 4477138fa0ae4e1b699786ef0600863ea6e6c61c ]

Same reasons than the ones explained in commit 4179cb5a4c92
("vxlan: test dev->flags & IFF_UP before calling netif_rx()")

netif_rx_ni() or napi_gro_frags() must be called under a strict contract.

At device dismantle phase, core networking clears IFF_UP
and flush_all_backlogs() is called after rcu grace period
to make sure no incoming packet might be in a cpu backlog
and still referencing the device.

A similar protocol is used for gro layer.

Most drivers call netif_rx() from their interrupt handler,
and since the interrupts are disabled at device dismantle,
netif_rx() does not have to check dev->flags & IFF_UP

Virtual drivers do not have this guarantee, and must
therefore make the check themselves.

Fixes: 1bd4978a88ac ("tun: honor IFF_UP in tun_get_user()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1763,9 +1763,6 @@ static ssize_t tun_get_user(struct tun_s
int skb_xdp = 1;
bool frags = tun_napi_frags_enabled(tfile);

- if (!(tun->dev->flags & IFF_UP))
- return -EIO;
-
if (!(tun->flags & IFF_NO_PI)) {
if (len < sizeof(pi))
return -EINVAL;
@@ -1867,6 +1864,8 @@ static ssize_t tun_get_user(struct tun_s
err = skb_copy_datagram_from_iter(skb, 0, from, len);

if (err) {
+ err = -EFAULT;
+drop:
this_cpu_inc(tun->pcpu_stats->rx_dropped);
kfree_skb(skb);
if (frags) {
@@ -1874,7 +1873,7 @@ static ssize_t tun_get_user(struct tun_s
mutex_unlock(&tfile->napi_mutex);
}

- return -EFAULT;
+ return err;
}
}

@@ -1958,6 +1957,12 @@ static ssize_t tun_get_user(struct tun_s
!tfile->detached)
rxhash = __skb_get_hash_symmetric(skb);

+ rcu_read_lock();
+ if (unlikely(!(tun->dev->flags & IFF_UP))) {
+ err = -EIO;
+ goto drop;
+ }
+
if (frags) {
/* Exercise flow dissector code path. */
u32 headlen = eth_get_headlen(skb->data, skb_headlen(skb));
@@ -1965,6 +1970,7 @@ static ssize_t tun_get_user(struct tun_s
if (unlikely(headlen > skb_headlen(skb))) {
this_cpu_inc(tun->pcpu_stats->rx_dropped);
napi_free_frags(&tfile->napi);
+ rcu_read_unlock();
mutex_unlock(&tfile->napi_mutex);
WARN_ON(1);
return -ENOMEM;
@@ -1992,6 +1998,7 @@ static ssize_t tun_get_user(struct tun_s
} else {
netif_rx_ni(skb);
}
+ rcu_read_unlock();

stats = get_cpu_ptr(tun->pcpu_stats);
u64_stats_update_begin(&stats->syncp);

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