The remote (hostile) process can set ring buffer indices to any value
at any time. If that happens, it is possible to get "buffer space"
(either for writing data, or ready for reading) negative or greater
than buffer size. This will end up with buffer overflow in the second
memcpy inside of do_send/do_recv.
Fix this by introducing new available bytes accessor functions
raw_get_data_ready and raw_get_buffer_space which are robust against
mad ring states, and only return sanitised values.
Proof sketch of correctness:
Now {rd,wr}_{cons,prod} are only ever used in the raw available bytes
functions, and in do_send and do_recv.
The raw available bytes functions do unsigned arithmetic on the
returned values. If the result is "negative" or too big it will be
>ring_size (since we used unsigned arithmetic). Otherwise the result
is a positive in-range value representing a reasonable ring state, in
which case we can safely convert it to int (as the rest of the code
expects).
do_send and do_recv immediately mask the ring index value with the
ring size. The result is always going to be plausible. If the ring
state has become mad, the worst case is that our behaviour is
inconsistent with the peer's ring pointer. I.e. we read or write to
arguably-incorrect parts of the ring - but always parts of the ring.
And of course if a peer misoperates the ring they can achieve this
effect anyway.
So the security problem is fixed.
This is XSA-86.
(The patch is essentially Ian Jackson's work, although parts of the
commit message are by Marek.)
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
master commit: 2efcb0193b
master date: 2014-02-06 16:44:41 +0100
-O2 -Wall -Werror triggers these warnings:
io.c: In function 'do_send':
io.c:196: warning: ignoring return value of 'writev', declared with attribute warn_unused_result
io.c: In function 'do_recv':
io.c:287: warning: ignoring return value of 'writev', declared with attribute warn_unused_result
writev to -1 will always fail, silence the warning by removing the offending
(disabled) debug code.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>
This library implements a bidirectional communication interface between
applications in different domains, similar to unix sockets. Data can be
sent using the byte-oriented libvchan_read/libvchan_write or the
packet-oriented libvchan_recv/libvchan_send.
Channel setup is done using a client-server model; domain IDs and a port
number must be negotiated prior to initialization. The server allocates
memory for the shared pages and determines the sizes of the
communication rings (which may span multiple pages, although the default
places rings and control within a single page).
With properly sized rings, testing has shown that this interface
provides speed comparable to pipes within a single Linux domain; it is
significantly faster than network-based communication.
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>
Marek Marczykowski-Górecki
Olaf Hering
Keir Fraser
Daniel De Graaf