diff options
| author | Tom Parkin <tparkin@katalix.com> | 2021-01-07 21:13:15 +0300 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2021-01-09 06:21:06 +0300 |
| commit | c1787ffd0d24eb93eefac2dbba0eac5700da9ff1 (patch) | |
| tree | 94c6123b8703bfcd561b99bfceaadff453e38b5a /drivers/net/ppp | |
| parent | fd2ddef043592e7de80af53f47fa46fd3573086e (diff) | |
| download | linux-c1787ffd0d24eb93eefac2dbba0eac5700da9ff1.tar.xz | |
ppp: fix refcount underflow on channel unbridge
When setting up a channel bridge, ppp_bridge_channels sets the
pch->bridge field before taking the associated reference on the bridge
file instance.
This opens up a refcount underflow bug if ppp_bridge_channels called
via. iotcl runs concurrently with ppp_unbridge_channels executing via.
file release.
The bug is triggered by ppp_bridge_channels taking the error path
through the 'err_unset' label. In this scenario, pch->bridge is set,
but the reference on the bridged channel will not be taken because
the function errors out. If ppp_unbridge_channels observes pch->bridge
before it is unset by the error path, it will erroneously drop the
reference on the bridged channel and cause a refcount underflow.
To avoid this, ensure that ppp_bridge_channels holds a reference on
each channel in advance of setting the bridge pointers.
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Fixes: 4cf476ced45d ("ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls")
Acked-by: Guillaume Nault <gnault@redhat.com>
Link: https://lore.kernel.org/r/20210107181315.3128-1-tparkin@katalix.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'drivers/net/ppp')
| -rw-r--r-- | drivers/net/ppp/ppp_generic.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 09c27f7773f9..d445ecb1d0c7 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -623,6 +623,7 @@ static int ppp_bridge_channels(struct channel *pch, struct channel *pchb) write_unlock_bh(&pch->upl); return -EALREADY; } + refcount_inc(&pchb->file.refcnt); rcu_assign_pointer(pch->bridge, pchb); write_unlock_bh(&pch->upl); @@ -632,19 +633,24 @@ static int ppp_bridge_channels(struct channel *pch, struct channel *pchb) write_unlock_bh(&pchb->upl); goto err_unset; } + refcount_inc(&pch->file.refcnt); rcu_assign_pointer(pchb->bridge, pch); write_unlock_bh(&pchb->upl); - refcount_inc(&pch->file.refcnt); - refcount_inc(&pchb->file.refcnt); - return 0; err_unset: write_lock_bh(&pch->upl); + /* Re-read pch->bridge with upl held in case it was modified concurrently */ + pchb = rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl)); RCU_INIT_POINTER(pch->bridge, NULL); write_unlock_bh(&pch->upl); synchronize_rcu(); + + if (pchb) + if (refcount_dec_and_test(&pchb->file.refcnt)) + ppp_destroy_channel(pchb); + return -EALREADY; } |