From d0d5c0cd1e711c98703f3544c1e6fc1372898de5 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 27 Aug 2019 10:13:46 +0100 Subject: 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: 248f219cb8bc ("rxrpc: Rewrite the data and ack handling code") Reported-by: Julian Wollrath Signed-off-by: David Howells --- net/rxrpc/rxkad.c | 32 +++++++++----------------------- 1 file changed, 9 insertions(+), 23 deletions(-) (limited to 'net/rxrpc/rxkad.c') 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 @@ 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; -- cgit v1.2.3-59-g8ed1b