[PATCH 5.7 020/265] rxrpc: Fix notification call on completion of discarded calls

Sasha Levin
2020-06-29T18:42:26Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit 0041cd5a50442db6e456b145892a0eaf2dff061f ]

When preallocated service calls are being discarded, they're passed to
->discard_new_call() to have the caller clean up any attached higher-layer
preallocated pieces before being marked completed. However, the act of
marking them completed now invokes the call's notification function - which
causes a problem because that function might assume that the previously
freed pieces of memory are still there.

Fix this by setting a dummy notification function on the socket after
calling ->discard_new_call().

This results in the following kasan message when the kafs module is
removed.

==================================================================
BUG: KASAN: use-after-free in afs_wake_up_async_call+0x6aa/0x770 fs/afs/rxrpc.c:707
Write of size 1 at addr ffff8880946c39e4 by task kworker/u4:1/21

CPU: 0 PID: 21 Comm: kworker/u4:1 Not tainted 5.8.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x413 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
afs_wake_up_async_call+0x6aa/0x770 fs/afs/rxrpc.c:707
rxrpc_notify_socket+0x1db/0x5d0 net/rxrpc/recvmsg.c:40
__rxrpc_set_call_completion.part.0+0x172/0x410 net/rxrpc/recvmsg.c:76
__rxrpc_call_completed net/rxrpc/recvmsg.c:112 [inline]
rxrpc_call_completed+0xca/0xf0 net/rxrpc/recvmsg.c:111
rxrpc_discard_prealloc+0x781/0xab0 net/rxrpc/call_accept.c:233
rxrpc_listen+0x147/0x360 net/rxrpc/af_rxrpc.c:245
afs_close_socket+0x95/0x320 fs/afs/rxrpc.c:110
afs_net_exit+0x1bc/0x310 fs/afs/main.c:155
ops_exit_list.isra.0+0xa8/0x150 net/core/net_namespace.c:186
cleanup_net+0x511/0xa50 net/core/net_namespace.c:603
process_one_work+0x965/0x1690 kernel/workqueue.c:2269
worker_thread+0x96/0xe10 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Allocated by task 6820:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc mm/kasan/common.c:494 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:467
kmem_cache_alloc_trace+0x153/0x7d0 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
afs_alloc_call+0x55/0x630 fs/afs/rxrpc.c:141
afs_charge_preallocation+0xe9/0x2d0 fs/afs/rxrpc.c:757
afs_open_socket+0x292/0x360 fs/afs/rxrpc.c:92
afs_net_init+0xa6c/0xe30 fs/afs/main.c:125
ops_init+0xaf/0x420 net/core/net_namespace.c:151
setup_net+0x2de/0x860 net/core/net_namespace.c:341
copy_net_ns+0x293/0x590 net/core/net_namespace.c:482
create_new_namespaces+0x3fb/0xb30 kernel/nsproxy.c:110
unshare_nsproxy_namespaces+0xbd/0x1f0 kernel/nsproxy.c:231
ksys_unshare+0x43d/0x8e0 kernel/fork.c:2983
__do_sys_unshare kernel/fork.c:3051 [inline]
__se_sys_unshare kernel/fork.c:3049 [inline]
__x64_sys_unshare+0x2d/0x40 kernel/fork.c:3049
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 21:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0xf7/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x109/0x2b0 mm/slab.c:3757
afs_put_call+0x585/0xa40 fs/afs/rxrpc.c:190
rxrpc_discard_prealloc+0x764/0xab0 net/rxrpc/call_accept.c:230
rxrpc_listen+0x147/0x360 net/rxrpc/af_rxrpc.c:245
afs_close_socket+0x95/0x320 fs/afs/rxrpc.c:110
afs_net_exit+0x1bc/0x310 fs/afs/main.c:155
ops_exit_list.isra.0+0xa8/0x150 net/core/net_namespace.c:186
cleanup_net+0x511/0xa50 net/core/net_namespace.c:603
process_one_work+0x965/0x1690 kernel/workqueue.c:2269
worker_thread+0x96/0xe10 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:291
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

The buggy address belongs to the object at ffff8880946c3800
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 484 bytes inside of
1024-byte region [ffff8880946c3800, ffff8880946c3c00)
The buggy address belongs to the page:
page:ffffea000251b0c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002546508 ffffea00024fa248 ffff8880aa000c40
raw: 0000000000000000 ffff8880946c3000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880946c3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880946c3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880946c3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880946c3a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880946c3a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Reported-by: syzbot+d3eccef36ddbd02713e9@syzkaller.appspotmail.com
Fixes: 5ac0d62226a0 ("rxrpc: Fix missing notification")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rxrpc/call_accept.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
index b7611cc159e51..032ed76c0166d 100644
--- a/net/rxrpc/call_accept.c
+++ b/net/rxrpc/call_accept.c
@@ -22,6 +22,11 @@
#include <net/ip.h>
#include "ar-internal.h"

+static void rxrpc_dummy_notify(struct sock *sk, struct rxrpc_call *call,
+ unsigned long user_call_ID)
+{
+}
+
/*
* Preallocate a single service call, connection and peer and, if possible,
* give them a user ID and attach the user's side of the ID to them.
@@ -228,6 +233,8 @@ void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
if (rx->discard_new_call) {
_debug("discard %lx", call->user_call_ID);
rx->discard_new_call(call, call->user_call_ID);
+ if (call->notify_rx)
+ call->notify_rx = rxrpc_dummy_notify;
rxrpc_put_call(call, rxrpc_call_put_kernel);
}
rxrpc_call_completed(call);
--
2.25.1