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Subject[PATCH net 5/5] rxrpc: Use skb_unshare() rather than skb_cow_data()
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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: 248f219cb8bc ("rxrpc: Rewrite the data and ack handling code")
Reported-by: Julian Wollrath <jwollrath@web.de>
Signed-off-by: David Howells <dhowells@redhat.com>
---

include/trace/events/rxrpc.h | 12 ++++++++----
net/rxrpc/ar-internal.h | 1 +
net/rxrpc/input.c | 18 ++++++++++++++++++
net/rxrpc/rxkad.c | 32 +++++++++-----------------------
net/rxrpc/skbuff.c | 25 ++++++++++++++++++++-----
5 files changed, 56 insertions(+), 32 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index e2356c51883b..a13a62db3565 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -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;
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 2d5294f3e62f..852e58781fda 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -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 *);
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 31090bdf1fae..d122c53c8697 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -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:
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index ae8cd8926456..c60c520fde7c 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -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;
diff --git a/net/rxrpc/skbuff.c b/net/rxrpc/skbuff.c
index 8e6f45f84b9b..0348d2bf6f7d 100644
--- a/net/rxrpc/skbuff.c
+++ b/net/rxrpc/skbuff.c
@@ -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);
}
}
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