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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: 248f219cb8 ("rxrpc: Rewrite the data and ack handling code")
Reported-by: Julian Wollrath <jwollrath@web.de>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells 2019-08-27 10:13:46 +01:00
parent 987db9f7cd
commit d0d5c0cd1e
5 changed files with 56 additions and 32 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/trace/events/rxrpc.h
View File

@ -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;

1
net/rxrpc/ar-internal.h
View File

@ -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 *);

18
net/rxrpc/input.c
View File

@ -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:

32
net/rxrpc/rxkad.c
View File

@ -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 @@ protocol_error:
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;

25
net/rxrpc/skbuff.c
View File

@ -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);
}
}