[Changelog stolen from Daniel Borkmann:]
Sasha Levin reported a suspicious rcu_dereference_protected() warning
found while fuzzing with trinity that is similar to this one:
[ 52.765684] net/core/filter.c:2262 suspicious rcu_dereference_protected()
usage!
[ 52.765688] other info that might help us debug this:
[ 52.765695] rcu_scheduler_active = 1, debug_locks = 1
[ 52.765701] 1 lock held by a.out/1525:
[ 52.765704] #0: (rtnl_mutex){+.+.+.}, at: [<ffffffff816a64b7>]
rtnl_lock+0x17/0x20
[ 52.765721] stack backtrace:
[ 52.765728] CPU: 1 PID: 1525 Comm: a.out Not tainted 4.5.0+ #264
[...]
[ 52.765768] Call Trace:
[ 52.765775] [<ffffffff813e488d>] dump_stack+0x85/0xc8
[ 52.765784] [<ffffffff810f2fa5>] lockdep_rcu_suspicious+0xd5/0x110
[ 52.765792] [<ffffffff816afdc2>] sk_detach_filter+0x82/0x90
[ 52.765801] [<ffffffffa0883425>] tun_detach_filter+0x35/0x90 [tun]
[ 52.765810] [<ffffffffa0884ed4>] __tun_chr_ioctl+0x354/0x1130 [tun]
[ 52.765818] [<ffffffff8136fed0>] ? selinux_file_ioctl+0x130/0x210
[ 52.765827] [<ffffffffa0885ce3>] tun_chr_ioctl+0x13/0x20 [tun]
[ 52.765834] [<ffffffff81260ea6>] do_vfs_ioctl+0x96/0x690
[ 52.765843] [<ffffffff81364af3>] ? security_file_ioctl+0x43/0x60
[ 52.765850] [<ffffffff81261519>] SyS_ioctl+0x79/0x90
[ 52.765858] [<ffffffff81003ba2>] do_syscall_64+0x62/0x140
[ 52.765866] [<ffffffff817d563f>] entry_SYSCALL64_slow_path+0x25/0x25
Same can be triggered with PROVE_RCU (+ PROVE_RCU_REPEATEDLY) enabled
from tun_attach_filter() when user space calls ioctl(tun_fd, TUN{ATTACH,
DETACH}FILTER, ...) for adding/removing a BPF filter on tap devices.
Since the fix in commit f91ff5b9ff52 ("net: sk_{detach|attach}_filter()
rcu fixes") sk_attach_filter()/sk_detach_filter() now dereferences the
filter with rcu_dereference_protected(), checking whether socket lock
is held in control path.
Since its introduction in commit 994051625981 ("tun: socket
filter support"), tap filters are managed under RTNL lock from
__tun_chr_ioctl(). Thus the sock_owned_by_user(sk) doesn't apply in this
specific case and therefore triggers the false positive.
Simply holding the locks during the filter updates will fix this problem.
Fixes: 994051625981 ("tun: socket filter support")
Reported-by: Sasha Levin <sasha.le...@oracle.com>
Cc: Daniel Borkmann <dan...@iogearbox.net>
Cc: Alexei Starovoitov <alexei.starovoi...@gmail.com>
Cc: Michal Kubecek <mkube...@suse.cz>
Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
drivers/net/tun.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index afdf950617c36e..dccbbacbbc7f02 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -622,7 +622,11 @@ static int tun_attach(struct tun_struct *tun, struct file
*file, bool skip_filte
/* Re-attach the filter to persist device */
if (!skip_filter && (tun->filter_attached == true)) {
+ bool slow;
+
+ slow = lock_sock_fast(tfile->socket.sk);
err = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+ unlock_sock_fast(tfile->socket.sk, slow);
if (!err)
goto out;
}
@@ -1821,8 +1825,12 @@ static void tun_detach_filter(struct tun_struct *tun,
int n)
struct tun_file *tfile;
for (i = 0; i < n; i++) {
+ bool slow;
+
tfile = rtnl_dereference(tun->tfiles[i]);
+ slow = lock_sock_fast(tfile->socket.sk);
sk_detach_filter(tfile->socket.sk);
+ unlock_sock_fast(tfile->socket.sk, slow);
}
tun->filter_attached = false;
@@ -1834,8 +1842,12 @@ static int tun_attach_filter(struct tun_struct *tun)
struct tun_file *tfile;
for (i = 0; i < tun->numqueues; i++) {
+ bool slow;
+
tfile = rtnl_dereference(tun->tfiles[i]);
+ slow = lock_sock_fast(tfile->socket.sk);
ret = sk_attach_filter(&tun->fprog, tfile->socket.sk);
+ unlock_sock_fast(tfile->socket.sk, slow);
if (ret) {
tun_detach_filter(tun, i);
return ret;
--
2.5.5
