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Commit d0d5c0cd authored by David Howells's avatar David Howells
Browse files

rxrpc: Use skb_unshare() rather than skb_cow_data() 



The in-place decryption routines in AF_RXRPC's rxkad security module
currently call skb_cow_data() to make sure the data isn't shared and that
the skb can be written over.  This has a problem, however, as the softirq
handler may be still holding a ref or the Rx ring may be holding multiple
refs when skb_cow_data() is called in rxkad_verify_packet() - and so
skb_shared() returns true and __pskb_pull_tail() dislikes that.  If this
occurs, something like the following report will be generated.

	kernel BUG at net/core/skbuff.c:1463!
	...
	RIP: 0010:pskb_expand_head+0x253/0x2b0
	...
	Call Trace:
	 __pskb_pull_tail+0x49/0x460
	 skb_cow_data+0x6f/0x300
	 rxkad_verify_packet+0x18b/0xb10 [rxrpc]
	 rxrpc_recvmsg_data.isra.11+0x4a8/0xa10 [rxrpc]
	 rxrpc_kernel_recv_data+0x126/0x240 [rxrpc]
	 afs_extract_data+0x51/0x2d0 [kafs]
	 afs_deliver_fs_fetch_data+0x188/0x400 [kafs]
	 afs_deliver_to_call+0xac/0x430 [kafs]
	 afs_wait_for_call_to_complete+0x22f/0x3d0 [kafs]
	 afs_make_call+0x282/0x3f0 [kafs]
	 afs_fs_fetch_data+0x164/0x300 [kafs]
	 afs_fetch_data+0x54/0x130 [kafs]
	 afs_readpages+0x20d/0x340 [kafs]
	 read_pages+0x66/0x180
	 __do_page_cache_readahead+0x188/0x1a0
	 ondemand_readahead+0x17d/0x2e0
	 generic_file_read_iter+0x740/0xc10
	 __vfs_read+0x145/0x1a0
	 vfs_read+0x8c/0x140
	 ksys_read+0x4a/0xb0
	 do_syscall_64+0x43/0xf0
	 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix this by using skb_unshare() instead in the input path for DATA packets
that have a security index != 0.  Non-DATA packets don't need in-place
encryption and neither do unencrypted DATA packets.

Fixes: 248f219c ("rxrpc: Rewrite the data and ack handling code")
Reported-by: default avatarJulian Wollrath <jwollrath@web.de>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
parent 987db9f7

include/trace/events/rxrpc.h

+8 −4
Original line number Diff line number Diff line
@@ -32,6 +32,8 @@ enum rxrpc_skb_trace { 
	rxrpc_skb_received,

	rxrpc_skb_rotated,

	rxrpc_skb_seen,

	rxrpc_skb_unshared,

	rxrpc_skb_unshared_nomem,

};



enum rxrpc_local_trace {
@@ -231,7 +233,9 @@ enum rxrpc_tx_point { 
	EM(rxrpc_skb_purged,			"PUR") \

	EM(rxrpc_skb_received,			"RCV") \

	EM(rxrpc_skb_rotated,			"ROT") \

	E_(rxrpc_skb_seen,			"SEE")

	EM(rxrpc_skb_seen,			"SEE") \

	EM(rxrpc_skb_unshared,			"UNS") \

	E_(rxrpc_skb_unshared_nomem,		"US0")



#define rxrpc_local_traces \

	EM(rxrpc_local_got,			"GOT") \
@@ -633,9 +637,9 @@ TRACE_EVENT(rxrpc_call, 


TRACE_EVENT(rxrpc_skb,

	    TP_PROTO(struct sk_buff *skb, enum rxrpc_skb_trace op,

		     int usage, int mod_count, const void *where),

		     int usage, int mod_count, u8 flags,    const void *where),



	    TP_ARGS(skb, op, usage, mod_count, where),

	    TP_ARGS(skb, op, usage, mod_count, flags, where),



	    TP_STRUCT__entry(

		    __field(struct sk_buff *,		skb		)
@@ -648,7 +652,7 @@ TRACE_EVENT(rxrpc_skb, 


	    TP_fast_assign(

		    __entry->skb = skb;

		    __entry->flags = rxrpc_skb(skb)->rx_flags;

		    __entry->flags = flags;

		    __entry->op = op;

		    __entry->usage = usage;

		    __entry->mod_count = mod_count;

net/rxrpc/ar-internal.h

+1 −0
Original line number Diff line number Diff line
@@ -1110,6 +1110,7 @@ void rxrpc_kernel_data_consumed(struct rxrpc_call *, struct sk_buff *); 
void rxrpc_packet_destructor(struct sk_buff *);

void rxrpc_new_skb(struct sk_buff *, enum rxrpc_skb_trace);

void rxrpc_see_skb(struct sk_buff *, enum rxrpc_skb_trace);

void rxrpc_eaten_skb(struct sk_buff *, enum rxrpc_skb_trace);

void rxrpc_get_skb(struct sk_buff *, enum rxrpc_skb_trace);

void rxrpc_free_skb(struct sk_buff *, enum rxrpc_skb_trace);

void rxrpc_purge_queue(struct sk_buff_head *);

net/rxrpc/input.c

+18 −0
Original line number Diff line number Diff line
@@ -1249,6 +1249,24 @@ int rxrpc_input_packet(struct sock *udp_sk, struct sk_buff *skb) 
			goto bad_message;

		if (!rxrpc_validate_data(skb))

			goto bad_message;



		/* Unshare the packet so that it can be modified for in-place

		 * decryption.

		 */

		if (sp->hdr.securityIndex != 0) {

			struct sk_buff *nskb = skb_unshare(skb, GFP_ATOMIC);

			if (!nskb) {

				rxrpc_eaten_skb(skb, rxrpc_skb_unshared_nomem);

				goto out;

			}



			if (nskb != skb) {

				rxrpc_eaten_skb(skb, rxrpc_skb_received);

				rxrpc_new_skb(skb, rxrpc_skb_unshared);

				skb = nskb;

				sp = rxrpc_skb(skb);

			}

		}

		break;



	case RXRPC_PACKET_TYPE_CHALLENGE:

net/rxrpc/rxkad.c

+9 −23
Original line number Diff line number Diff line
@@ -187,10 +187,8 @@ static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call, 
	struct rxrpc_skb_priv *sp;

	struct rxrpc_crypt iv;

	struct scatterlist sg[16];

	struct sk_buff *trailer;

	unsigned int len;

	u16 check;

	int nsg;

	int err;



	sp = rxrpc_skb(skb);
@@ -214,15 +212,14 @@ static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call, 
	crypto_skcipher_encrypt(req);



	/* we want to encrypt the skbuff in-place */

	nsg = skb_cow_data(skb, 0, &trailer);

	err = -ENOMEM;

	if (nsg < 0 || nsg > 16)

	err = -EMSGSIZE;

	if (skb_shinfo(skb)->nr_frags > 16)

		goto out;



	len = data_size + call->conn->size_align - 1;

	len &= ~(call->conn->size_align - 1);



	sg_init_table(sg, nsg);

	sg_init_table(sg, ARRAY_SIZE(sg));

	err = skb_to_sgvec(skb, sg, 0, len);

	if (unlikely(err < 0))

		goto out;
@@ -319,11 +316,10 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb, 
	struct rxkad_level1_hdr sechdr;

	struct rxrpc_crypt iv;

	struct scatterlist sg[16];

	struct sk_buff *trailer;

	bool aborted;

	u32 data_size, buf;

	u16 check;

	int nsg, ret;

	int ret;



	_enter("");
@@ -336,11 +332,7 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb, 
	/* Decrypt the skbuff in-place.  TODO: We really want to decrypt

	 * directly into the target buffer.

	 */

	nsg = skb_cow_data(skb, 0, &trailer);

	if (nsg < 0 || nsg > 16)

		goto nomem;



	sg_init_table(sg, nsg);

	sg_init_table(sg, ARRAY_SIZE(sg));

	ret = skb_to_sgvec(skb, sg, offset, 8);

	if (unlikely(ret < 0))

		return ret;
@@ -388,10 +380,6 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb, 
	if (aborted)

		rxrpc_send_abort_packet(call);

	return -EPROTO;



nomem:

	_leave(" = -ENOMEM");

	return -ENOMEM;

}



/*
@@ -406,7 +394,6 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb, 
	struct rxkad_level2_hdr sechdr;

	struct rxrpc_crypt iv;

	struct scatterlist _sg[4], *sg;

	struct sk_buff *trailer;

	bool aborted;

	u32 data_size, buf;

	u16 check;
@@ -423,12 +410,11 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb, 
	/* Decrypt the skbuff in-place.  TODO: We really want to decrypt

	 * directly into the target buffer.

	 */

	nsg = skb_cow_data(skb, 0, &trailer);

	if (nsg < 0)

		goto nomem;



	sg = _sg;

	if (unlikely(nsg > 4)) {

	nsg = skb_shinfo(skb)->nr_frags;

	if (nsg <= 4) {

		nsg = 4;

	} else {

		sg = kmalloc_array(nsg, sizeof(*sg), GFP_NOIO);

		if (!sg)

			goto nomem;

net/rxrpc/skbuff.c

+20 −5
Original line number Diff line number Diff line
@@ -24,7 +24,8 @@ void rxrpc_new_skb(struct sk_buff *skb, enum rxrpc_skb_trace op) 
{

	const void *here = __builtin_return_address(0);

	int n = atomic_inc_return(select_skb_count(skb));

	trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n, here);

	trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n,

			rxrpc_skb(skb)->rx_flags, here);

}



/*
@@ -35,7 +36,8 @@ void rxrpc_see_skb(struct sk_buff *skb, enum rxrpc_skb_trace op) 
	const void *here = __builtin_return_address(0);

	if (skb) {

		int n = atomic_read(select_skb_count(skb));

		trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n, here);

		trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n,

				rxrpc_skb(skb)->rx_flags, here);

	}

}
@@ -46,10 +48,21 @@ void rxrpc_get_skb(struct sk_buff *skb, enum rxrpc_skb_trace op) 
{

	const void *here = __builtin_return_address(0);

	int n = atomic_inc_return(select_skb_count(skb));

	trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n, here);

	trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n,

			rxrpc_skb(skb)->rx_flags, here);

	skb_get(skb);

}



/*

 * Note the dropping of a ref on a socket buffer by the core.

 */

void rxrpc_eaten_skb(struct sk_buff *skb, enum rxrpc_skb_trace op)

{

	const void *here = __builtin_return_address(0);

	int n = atomic_inc_return(&rxrpc_n_rx_skbs);

	trace_rxrpc_skb(skb, op, 0, n, 0, here);

}



/*

 * Note the destruction of a socket buffer.

 */
@@ -60,7 +73,8 @@ void rxrpc_free_skb(struct sk_buff *skb, enum rxrpc_skb_trace op) 
		int n;

		CHECK_SLAB_OKAY(&skb->users);

		n = atomic_dec_return(select_skb_count(skb));

		trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n, here);

		trace_rxrpc_skb(skb, op, refcount_read(&skb->users), n,

				rxrpc_skb(skb)->rx_flags, here);

		kfree_skb(skb);

	}

}
@@ -75,7 +89,8 @@ void rxrpc_purge_queue(struct sk_buff_head *list) 
	while ((skb = skb_dequeue((list))) != NULL) {

		int n = atomic_dec_return(select_skb_count(skb));

		trace_rxrpc_skb(skb, rxrpc_skb_purged,

				refcount_read(&skb->users), n, here);

				refcount_read(&skb->users), n,

				rxrpc_skb(skb)->rx_flags, here);

		kfree_skb(skb);

	}

}