Since commit 552d0e17ea04 ("sunrpc: convert queue_wait from global to
per-cache-detail waitqueue") poll() and epoll queue their waiters for a
channel file on the queue_wait head in struct cache_detail. But the
cache_detail can be freed while its channel file is still open and
waited on.
The procfs channel files of a network namespace are removed when the
namespace goes away. Removing a procfs file waits for the callers that
are in one of its methods right now and then calls ->release on every
file that is still open (cf. close_pdeo()). The waiters that poll() and
epoll left on the head stay queued until their file is really closed.
So:
sunrpc_exit_net()
-> ip_map_cache_destroy()
-> cache_unregister_net()
-> remove_cache_proc_entries()
-> proc_remove() // ->release, the waiters stay queued
-> cache_destroy_net() // kfree(cd)
and when poll() returns remove_wait_queue() writes to the freed
cache_detail:
BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x4b/0xa0
Read of size 1 at addr ff110001131bb570 by task sunrpc-poll-uaf/242
Call Trace:
remove_wait_queue+0x22/0x1c0
poll_freewait+0xc2/0x230
do_sys_poll+0x9ba/0xd50
__x64_sys_poll+0x165/0x470
Freed by task 12:
kfree+0x267/0x620
sunrpc_exit_net+0x34/0x80
ops_undo_list+0x271/0x8d0
cleanup_net+0x3f3/0x860
Closing an epoll instance that watches the file gets there through
ep_unregister_pollwait() instead.
The channel files of a network namespace belong to the root of its
user namespace and cache_open() doesn't check for a capability. So an
unprivileged user can open the channel file of a namespace of its own
from the outside, poll it and let the namespace die.
Go back to a single static wait queue that never goes away. A wakeup
for one cache wakes the waiters of all caches again but cache_poll()
reports per cache_detail so that's just a spurious wakeup. procfs
should really own the wait queue of its files like kernfs does but
that's nothing for stable.
Reported-by: Chris Mason <[email protected]>
Fixes: 552d0e17ea04 ("sunrpc: convert queue_wait from global to
per-cache-detail waitqueue")
Cc: [email protected]
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
---
include/linux/sunrpc/cache.h | 1 -
net/sunrpc/cache.c | 12 +++++++++---
2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
index 2735c332ddb7..bf4fc543e1e5 100644
--- a/include/linux/sunrpc/cache.h
+++ b/include/linux/sunrpc/cache.h
@@ -119,7 +119,6 @@ struct cache_detail {
struct list_head requests;
struct list_head readers;
spinlock_t queue_lock;
- wait_queue_head_t queue_wait;
u64 next_seqno;
atomic_t writers; /* how many time is
/channel open */
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 1bc04109d213..1ceaea7e01b9 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -404,7 +404,6 @@ void sunrpc_init_cache_detail(struct cache_detail *cd)
INIT_LIST_HEAD(&cd->requests);
INIT_LIST_HEAD(&cd->readers);
spin_lock_init(&cd->queue_lock);
- init_waitqueue_head(&cd->queue_wait);
cd->next_seqno = 1;
spin_lock(&cache_list_lock);
cd->nextcheck = 0;
@@ -965,13 +964,20 @@ static ssize_t cache_write(struct file *filp, const char
__user *buf,
return ret;
}
+/*
+ * Not in struct cache_detail: poll and epoll waiters stay queued until
+ * their file is closed, but a channel file in procfs can stay open after
+ * the cache_detail of its dying network namespace has been freed.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(queue_wait);
+
static __poll_t cache_poll(struct file *filp, poll_table *wait,
struct cache_detail *cd)
{
__poll_t mask;
struct cache_reader *rp = filp->private_data;
- poll_wait(filp, &cd->queue_wait, wait);
+ poll_wait(filp, &queue_wait, wait);
/* alway allow write */
mask = EPOLLOUT | EPOLLWRNORM;
@@ -1236,7 +1242,7 @@ static int cache_do_upcall(struct cache_detail *detail,
struct cache_head *h)
spin_unlock(&detail->queue_lock);
if (ret != -EAGAIN && detail->cache_notify)
detail->cache_notify(detail, h);
- wake_up(&detail->queue_wait);
+ wake_up(&queue_wait);
if (ret == -EAGAIN) {
kfree(buf);
kfree(crq);
--
2.53.0
