net: fix unsafe set_memory_rw from softirq

on x86 system with net.core.bpf_jit_enable = 1

sudo tcpdump -i eth1 'tcp port 22'

causes the warning:
[ 56.766097] Possible unsafe locking scenario:
[ 56.766097]
[ 56.780146] CPU0
[ 56.786807] ----
[ 56.793188] lock(&(&vb->lock)->rlock);
[ 56.799593] <Interrupt>
[ 56.805889] lock(&(&vb->lock)->rlock);
[ 56.812266]
[ 56.812266] *** DEADLOCK ***
[ 56.812266]
[ 56.830670] 1 lock held by ksoftirqd/1/13:
[ 56.836838] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff8118f44c>] vm_unmap_aliases+0x8c/0x380
[ 56.849757]
[ 56.849757] stack backtrace:
[ 56.862194] CPU: 1 PID: 13 Comm: ksoftirqd/1 Not tainted 3.12.0-rc3+ #45
[ 56.868721] Hardware name: System manufacturer System Product Name/P8Z77 WS, BIOS 3007 07/26/2012
[ 56.882004] ffffffff821944c0 ffff88080bbdb8c8 ffffffff8175a145 0000000000000007
[ 56.895630] ffff88080bbd5f40 ffff88080bbdb928 ffffffff81755b14 0000000000000001
[ 56.909313] ffff880800000001 ffff880800000000 ffffffff8101178f 0000000000000001
[ 56.923006] Call Trace:
[ 56.929532] [<ffffffff8175a145>] dump_stack+0x55/0x76
[ 56.936067] [<ffffffff81755b14>] print_usage_bug+0x1f7/0x208
[ 56.942445] [<ffffffff8101178f>] ? save_stack_trace+0x2f/0x50
[ 56.948932] [<ffffffff810cc0a0>] ? check_usage_backwards+0x150/0x150
[ 56.955470] [<ffffffff810ccb52>] mark_lock+0x282/0x2c0
[ 56.961945] [<ffffffff810ccfed>] __lock_acquire+0x45d/0x1d50
[ 56.968474] [<ffffffff810cce6e>] ? __lock_acquire+0x2de/0x1d50
[ 56.975140] [<ffffffff81393bf5>] ? cpumask_next_and+0x55/0x90
[ 56.981942] [<ffffffff810cef72>] lock_acquire+0x92/0x1d0
[ 56.988745] [<ffffffff8118f52a>] ? vm_unmap_aliases+0x16a/0x380
[ 56.995619] [<ffffffff817628f1>] _raw_spin_lock+0x41/0x50
[ 57.002493] [<ffffffff8118f52a>] ? vm_unmap_aliases+0x16a/0x380
[ 57.009447] [<ffffffff8118f52a>] vm_unmap_aliases+0x16a/0x380
[ 57.016477] [<ffffffff8118f44c>] ? vm_unmap_aliases+0x8c/0x380
[ 57.023607] [<ffffffff810436b0>] change_page_attr_set_clr+0xc0/0x460
[ 57.030818] [<ffffffff810cfb8d>] ? trace_hardirqs_on+0xd/0x10
[ 57.037896] [<ffffffff811a8330>] ? kmem_cache_free+0xb0/0x2b0
[ 57.044789] [<ffffffff811b59c3>] ? free_object_rcu+0x93/0xa0
[ 57.051720] [<ffffffff81043d9f>] set_memory_rw+0x2f/0x40
[ 57.058727] [<ffffffff8104e17c>] bpf_jit_free+0x2c/0x40
[ 57.065577] [<ffffffff81642cba>] sk_filter_release_rcu+0x1a/0x30
[ 57.072338] [<ffffffff811108e2>] rcu_process_callbacks+0x202/0x7c0
[ 57.078962] [<ffffffff81057f17>] __do_softirq+0xf7/0x3f0
[ 57.085373] [<ffffffff81058245>] run_ksoftirqd+0x35/0x70

cannot reuse jited filter memory, since it's readonly,
so use original bpf insns memory to hold work_struct

defer kfree of sk_filter until jit completed freeing

tested on x86_64 and i386

Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

arch/arm/net/bpf_jit_32.c

···
 {
 	if (fp->bpf_func != sk_run_filter)
 		module_free(NULL, fp->bpf_func);
+	kfree(fp);
 }

arch/powerpc/net/bpf_jit_comp.c

···
 {
 	if (fp->bpf_func != sk_run_filter)
 		module_free(NULL, fp->bpf_func);
+	kfree(fp);
 }

arch/s390/net/bpf_jit_comp.c

···
 	struct bpf_binary_header *header = (void *)addr;
 
 	if (fp->bpf_func == sk_run_filter)
-		return;
+		goto free_filter;
 	set_memory_rw(addr, header->pages);
 	module_free(NULL, header);
+free_filter:
+	kfree(fp);
 }

arch/sparc/net/bpf_jit_comp.c

···
 {
 	if (fp->bpf_func != sk_run_filter)
 		module_free(NULL, fp->bpf_func);
+	kfree(fp);
 }

arch/x86/net/bpf_jit_comp.c

···
 	return;
 }
 
+static void bpf_jit_free_deferred(struct work_struct *work)
+{
+	struct sk_filter *fp = container_of(work, struct sk_filter, work);
+	unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
+	struct bpf_binary_header *header = (void *)addr;
+
+	set_memory_rw(addr, header->pages);
+	module_free(NULL, header);
+	kfree(fp);
+}
+
 void bpf_jit_free(struct sk_filter *fp)
 {
 	if (fp->bpf_func != sk_run_filter) {
-		unsigned long addr = (unsigned long)fp->bpf_func & PAGE_MASK;
-		struct bpf_binary_header *header = (void *)addr;
-
-		set_memory_rw(addr, header->pages);
-		module_free(NULL, header);
+		INIT_WORK(&fp->work, bpf_jit_free_deferred);
+		schedule_work(&fp->work);
 	}
 }

include/linux/filter.h

···
 
 #include <linux/atomic.h>
 #include <linux/compat.h>
+#include <linux/workqueue.h>
 #include <uapi/linux/filter.h>
 
 #ifdef CONFIG_COMPAT
···
 {
 	atomic_t		refcnt;
 	unsigned int         	len;	/* Number of filter blocks */
+	struct rcu_head		rcu;
 	unsigned int		(*bpf_func)(const struct sk_buff *skb,
 					    const struct sock_filter *filter);
-	struct rcu_head		rcu;
-	struct sock_filter     	insns[0];
+	union {
+		struct sock_filter     	insns[0];
+		struct work_struct	work;
+	};
 };
 
-static inline unsigned int sk_filter_len(const struct sk_filter *fp)
+static inline unsigned int sk_filter_size(unsigned int proglen)
 {
-	return fp->len * sizeof(struct sock_filter) + sizeof(*fp);
+	return max(sizeof(struct sk_filter),
+		   offsetof(struct sk_filter, insns[proglen]));
 }
 
 extern int sk_filter(struct sock *sk, struct sk_buff *skb);
···
 }
 #define SK_RUN_FILTER(FILTER, SKB) (*FILTER->bpf_func)(SKB, FILTER->insns)
 #else
+#include <linux/slab.h>
 static inline void bpf_jit_compile(struct sk_filter *fp)
 {
 }
 static inline void bpf_jit_free(struct sk_filter *fp)
 {
+	kfree(fp);
 }
 #define SK_RUN_FILTER(FILTER, SKB) sk_run_filter(SKB, FILTER->insns)
 #endif

include/net/sock.h

···
 
 static inline void sk_filter_uncharge(struct sock *sk, struct sk_filter *fp)
 {
-	unsigned int size = sk_filter_len(fp);
-
-	atomic_sub(size, &sk->sk_omem_alloc);
+	atomic_sub(sk_filter_size(fp->len), &sk->sk_omem_alloc);
 	sk_filter_release(fp);
 }
 
 static inline void sk_filter_charge(struct sock *sk, struct sk_filter *fp)
 {
 	atomic_inc(&fp->refcnt);
-	atomic_add(sk_filter_len(fp), &sk->sk_omem_alloc);
+	atomic_add(sk_filter_size(fp->len), &sk->sk_omem_alloc);
 }
 
 /*

net/core/filter.c

···
 	struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 
 	bpf_jit_free(fp);
-	kfree(fp);
 }
 EXPORT_SYMBOL(sk_filter_release_rcu);
 
···
 	if (fprog->filter == NULL)
 		return -EINVAL;
 
-	fp = kmalloc(fsize + sizeof(*fp), GFP_KERNEL);
+	fp = kmalloc(sk_filter_size(fprog->len), GFP_KERNEL);
 	if (!fp)
 		return -ENOMEM;
 	memcpy(fp->insns, fprog->filter, fsize);
···
 {
 	struct sk_filter *fp, *old_fp;
 	unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
+	unsigned int sk_fsize = sk_filter_size(fprog->len);
 	int err;
 
 	if (sock_flag(sk, SOCK_FILTER_LOCKED))
···
 	if (fprog->filter == NULL)
 		return -EINVAL;
 
-	fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
+	fp = sock_kmalloc(sk, sk_fsize, GFP_KERNEL);
 	if (!fp)
 		return -ENOMEM;
 	if (copy_from_user(fp->insns, fprog->filter, fsize)) {
-		sock_kfree_s(sk, fp, fsize+sizeof(*fp));
+		sock_kfree_s(sk, fp, sk_fsize);
 		return -EFAULT;
 	}