path: root/net/rxrpc/call_object.c
diff options
authorDavid Howells <dhowells@redhat.com>2020-07-29 00:03:56 +0100
committerDavid S. Miller <davem@davemloft.net>2020-07-30 16:50:20 -0700
commit65550098c1c4db528400c73acf3e46bfa78d9264 (patch)
treea2395038071fde9b06e78294920cecfd564484d9 /net/rxrpc/call_object.c
parent591eee6d0783d4a0d7f0e7c4effdba9cf6c1e2c5 (diff)
rxrpc: Fix race between recvmsg and sendmsg on immediate call failure
There's a race between rxrpc_sendmsg setting up a call, but then failing to send anything on it due to an error, and recvmsg() seeing the call completion occur and trying to return the state to the user. An assertion fails in rxrpc_recvmsg() because the call has already been released from the socket and is about to be released again as recvmsg deals with it. (The recvmsg_q queue on the socket holds a ref, so there's no problem with use-after-free.) We also have to be careful not to end up reporting an error twice, in such a way that both returns indicate to userspace that the user ID supplied with the call is no longer in use - which could cause the client to malfunction if it recycles the user ID fast enough. Fix this by the following means: (1) When sendmsg() creates a call after the point that the call has been successfully added to the socket, don't return any errors through sendmsg(), but rather complete the call and let recvmsg() retrieve them. Make sendmsg() return 0 at this point. Further calls to sendmsg() for that call will fail with ESHUTDOWN. Note that at this point, we haven't send any packets yet, so the server doesn't yet know about the call. (2) If sendmsg() returns an error when it was expected to create a new call, it means that the user ID wasn't used. (3) Mark the call disconnected before marking it completed to prevent an oops in rxrpc_release_call(). (4) recvmsg() will then retrieve the error and set MSG_EOR to indicate that the user ID is no longer known by the kernel. An oops like the following is produced: kernel BUG at net/rxrpc/recvmsg.c:605! ... RIP: 0010:rxrpc_recvmsg+0x256/0x5ae ... Call Trace: ? __init_waitqueue_head+0x2f/0x2f ____sys_recvmsg+0x8a/0x148 ? import_iovec+0x69/0x9c ? copy_msghdr_from_user+0x5c/0x86 ___sys_recvmsg+0x72/0xaa ? __fget_files+0x22/0x57 ? __fget_light+0x46/0x51 ? fdget+0x9/0x1b do_recvmmsg+0x15e/0x232 ? _raw_spin_unlock+0xa/0xb ? vtime_delta+0xf/0x25 __x64_sys_recvmmsg+0x2c/0x2f do_syscall_64+0x4c/0x78 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Fixes: 357f5ef64628 ("rxrpc: Call rxrpc_release_call() on error in rxrpc_new_client_call()") Reported-by: syzbot+b54969381df354936d96@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/rxrpc/call_object.c')
1 files changed, 19 insertions, 8 deletions
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index f07970207b54..38a46167523f 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -288,7 +288,7 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
ret = rxrpc_connect_call(rx, call, cp, srx, gfp);
if (ret < 0)
- goto error;
+ goto error_attached_to_socket;
trace_rxrpc_call(call->debug_id, rxrpc_call_connected,
atomic_read(&call->usage), here, NULL);
@@ -308,18 +308,29 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
- ret = -EEXIST;
__rxrpc_set_call_completion(call, RXRPC_CALL_LOCAL_ERROR,
- RX_CALL_DEAD, ret);
trace_rxrpc_call(call->debug_id, rxrpc_call_error,
- atomic_read(&call->usage), here, ERR_PTR(ret));
+ atomic_read(&call->usage), here, ERR_PTR(-EEXIST));
rxrpc_release_call(rx, call);
rxrpc_put_call(call, rxrpc_call_put);
- _leave(" = %d", ret);
- return ERR_PTR(ret);
+ _leave(" = -EEXIST");
+ return ERR_PTR(-EEXIST);
+ /* We got an error, but the call is attached to the socket and is in
+ * need of release. However, we might now race with recvmsg() when
+ * completing the call queues it. Return 0 from sys_sendmsg() and
+ * leave the error to recvmsg() to deal with.
+ */
+ trace_rxrpc_call(call->debug_id, rxrpc_call_error,
+ atomic_read(&call->usage), here, ERR_PTR(ret));
+ set_bit(RXRPC_CALL_DISCONNECTED, &call->flags);
+ __rxrpc_set_call_completion(call, RXRPC_CALL_LOCAL_ERROR,
+ RX_CALL_DEAD, ret);
+ _leave(" = c=%08x [err]", call->debug_id);
+ return call;