rxrpc: Work around usercopy check
authorDavid Howells <dhowells@redhat.com>
Thu, 15 Feb 2018 22:59:00 +0000 (22:59 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 30 May 2018 05:50:28 +0000 (07:50 +0200)
commitf55ec6a8d856ffbd53e7424207e722c3c3eb5c2d
treecf1893ab5e2e6e6d206548775286cea49c7c93f3
parent69b28c18f7c8b3bbdc037f1cc029acc21723b997
rxrpc: Work around usercopy check

[ Upstream commit a16b8d0cf2ec1e626d24bc2a7b9e64ace6f7501d ]

Due to a check recently added to copy_to_user(), it's now not permitted to
copy from slab-held data to userspace unless the slab is whitelisted.  This
affects rxrpc_recvmsg() when it attempts to place an RXRPC_USER_CALL_ID
control message in the userspace control message buffer.  A warning is
generated by usercopy_warn() because the source is the copy of the
user_call_ID retained in the rxrpc_call struct.

Work around the issue by copying the user_call_ID to a variable on the
stack and passing that to put_cmsg().

The warning generated looks like:

Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLUB object 'dmaengine-unmap-128' (offset 680, size 8)!
WARNING: CPU: 0 PID: 1401 at mm/usercopy.c:81 usercopy_warn+0x7e/0xa0
...
RIP: 0010:usercopy_warn+0x7e/0xa0
...
Call Trace:
 __check_object_size+0x9c/0x1a0
 put_cmsg+0x98/0x120
 rxrpc_recvmsg+0x6fc/0x1010 [rxrpc]
 ? finish_wait+0x80/0x80
 ___sys_recvmsg+0xf8/0x240
 ? __clear_rsb+0x25/0x3d
 ? __clear_rsb+0x15/0x3d
 ? __clear_rsb+0x25/0x3d
 ? __clear_rsb+0x15/0x3d
 ? __clear_rsb+0x25/0x3d
 ? __clear_rsb+0x15/0x3d
 ? __clear_rsb+0x25/0x3d
 ? __clear_rsb+0x15/0x3d
 ? finish_task_switch+0xa6/0x2b0
 ? trace_hardirqs_on_caller+0xed/0x180
 ? _raw_spin_unlock_irq+0x29/0x40
 ? __sys_recvmsg+0x4e/0x90
 __sys_recvmsg+0x4e/0x90
 do_syscall_64+0x7a/0x220
 entry_SYSCALL_64_after_hwframe+0x26/0x9b

Reported-by: Jonathan Billings <jsbillings@jsbillings.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Jonathan Billings <jsbillings@jsbillings.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
net/rxrpc/recvmsg.c