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authorDaniel Borkmann <daniel@iogearbox.net>2016-03-31 02:13:18 +0200
committerDavid S. Miller <davem@davemloft.net>2016-04-01 14:33:46 -0400
commit5a5abb1fa3b05dd6aa821525832644c1e7d2905f (patch)
treef6b9a82511558e0c9d456194db3fc702ca7411da /net/core
parent79f4223257bfef52b0a26d0d7ad4019e764be6ce (diff)
tun, bpf: fix suspicious RCU usage in tun_{attach, detach}_filter
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 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 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. Extend the BPF API with __sk_attach_filter()/__sk_detach_filter() pair that is used by tap filters and pass in lockdep_rtnl_is_held() for the rcu_dereference_protected() checks instead. Reported-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/filter.c33
1 files changed, 21 insertions, 12 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 4b81b71171b4..ca7f832b2980 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1149,7 +1149,8 @@ void bpf_prog_destroy(struct bpf_prog *fp)
}
EXPORT_SYMBOL_GPL(bpf_prog_destroy);
-static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
+static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk,
+ bool locked)
{
struct sk_filter *fp, *old_fp;
@@ -1165,10 +1166,8 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
return -ENOMEM;
}
- old_fp = rcu_dereference_protected(sk->sk_filter,
- sock_owned_by_user(sk));
+ old_fp = rcu_dereference_protected(sk->sk_filter, locked);
rcu_assign_pointer(sk->sk_filter, fp);
-
if (old_fp)
sk_filter_uncharge(sk, old_fp);
@@ -1247,7 +1246,8 @@ struct bpf_prog *__get_filter(struct sock_fprog *fprog, struct sock *sk)
* occurs or there is insufficient memory for the filter a negative
* errno code is returned. On success the return is zero.
*/
-int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
+int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk,
+ bool locked)
{
struct bpf_prog *prog = __get_filter(fprog, sk);
int err;
@@ -1255,7 +1255,7 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
if (IS_ERR(prog))
return PTR_ERR(prog);
- err = __sk_attach_prog(prog, sk);
+ err = __sk_attach_prog(prog, sk, locked);
if (err < 0) {
__bpf_prog_release(prog);
return err;
@@ -1263,7 +1263,12 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
return 0;
}
-EXPORT_SYMBOL_GPL(sk_attach_filter);
+EXPORT_SYMBOL_GPL(__sk_attach_filter);
+
+int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
+{
+ return __sk_attach_filter(fprog, sk, sock_owned_by_user(sk));
+}
int sk_reuseport_attach_filter(struct sock_fprog *fprog, struct sock *sk)
{
@@ -1309,7 +1314,7 @@ int sk_attach_bpf(u32 ufd, struct sock *sk)
if (IS_ERR(prog))
return PTR_ERR(prog);
- err = __sk_attach_prog(prog, sk);
+ err = __sk_attach_prog(prog, sk, sock_owned_by_user(sk));
if (err < 0) {
bpf_prog_put(prog);
return err;
@@ -2250,7 +2255,7 @@ static int __init register_sk_filter_ops(void)
}
late_initcall(register_sk_filter_ops);
-int sk_detach_filter(struct sock *sk)
+int __sk_detach_filter(struct sock *sk, bool locked)
{
int ret = -ENOENT;
struct sk_filter *filter;
@@ -2258,8 +2263,7 @@ int sk_detach_filter(struct sock *sk)
if (sock_flag(sk, SOCK_FILTER_LOCKED))
return -EPERM;
- filter = rcu_dereference_protected(sk->sk_filter,
- sock_owned_by_user(sk));
+ filter = rcu_dereference_protected(sk->sk_filter, locked);
if (filter) {
RCU_INIT_POINTER(sk->sk_filter, NULL);
sk_filter_uncharge(sk, filter);
@@ -2268,7 +2272,12 @@ int sk_detach_filter(struct sock *sk)
return ret;
}
-EXPORT_SYMBOL_GPL(sk_detach_filter);
+EXPORT_SYMBOL_GPL(__sk_detach_filter);
+
+int sk_detach_filter(struct sock *sk)
+{
+ return __sk_detach_filter(sk, sock_owned_by_user(sk));
+}
int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf,
unsigned int len)