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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: 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
Download Patch File Download Diff File Expand all files Collapse all files

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: