From 118d527f2e4baec5fe8060b22a6212468b8e4d3f Mon Sep 17 00:00:00 2001

From: Michael Tokarev <mjt@tls.msk.ru>

Date: Wed, 1 Sep 2021 16:16:24 +0300

Subject: [PATCH] qemu-sockets: fix unix socket path copy (again)

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Commit 4cfd970ec188558daa6214f26203fe553fb1e01f added an

assert which ensures the path within an address of a unix

socket returned from the kernel is at least one byte and

does not exceed sun_path buffer. Both of this constraints

are wrong:

A unix socket can be unnamed, in this case the path is

completely empty (not even \0)

And some implementations (notable linux) can add extra

trailing byte (\0) _after_ the sun_path buffer if we

passed buffer larger than it (and we do).

So remove the assertion (since it causes real-life breakage)

but at the same time fix the usage of sun_path. Namely,

we should not access sun_path[0] if kernel did not return

it at all (this is the case for unnamed sockets),

and use the returned salen when copyig actual path as an

upper constraint for the amount of bytes to copy - this

will ensure we wont exceed the information provided by

the kernel, regardless whenever there is a trailing \0

or not. This also helps with unnamed sockets.

Note the case of abstract socket, the sun_path is actually

a blob and can contain \0 characters, - it should not be

passed to g_strndup and the like, it should be accessed by

memcpy-like functions.

Fixes: 4cfd970ec188558daa6214f26203fe553fb1e01f

Fixes: http://bugs.debian.org/993145

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

CC: qemu-stable@nongnu.org

---

 util/qemu-sockets.c | 13 +++++--------

 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c

index f2f3676d1f..c5043999e9 100644

--- a/util/qemu-sockets.c

+++ b/util/qemu-sockets.c

@@ -1345,25 +1345,22 @@ socket_sockaddr_to_address_unix(struct sockaddr_storage *sa,

     SocketAddress *addr;

     struct sockaddr_un *su = (struct sockaddr_un *)sa;

-    assert(salen >= sizeof(su->sun_family) + 1 &&

-           salen <= sizeof(struct sockaddr_un));

-

     addr = g_new0(SocketAddress, 1);

     addr->type = SOCKET_ADDRESS_TYPE_UNIX;

+    salen -= offsetof(struct sockaddr_un, sun_path);

 #ifdef CONFIG_LINUX

-    if (!su->sun_path[0]) {

+    if (salen > 0 && !su->sun_path[0]) {

         /* Linux abstract socket */

-        addr->u.q_unix.path = g_strndup(su->sun_path + 1,

-                                        salen - sizeof(su->sun_family) - 1);

+        addr->u.q_unix.path = g_strndup(su->sun_path + 1, salen - 1);

         addr->u.q_unix.has_abstract = true;

         addr->u.q_unix.abstract = true;

         addr->u.q_unix.has_tight = true;

-        addr->u.q_unix.tight = salen < sizeof(*su);

+        addr->u.q_unix.tight = salen < sizeof(su->sun_path);

         return addr;

     }

 #endif

-    addr->u.q_unix.path = g_strndup(su->sun_path, sizeof(su->sun_path));

+    addr->u.q_unix.path = g_strndup(su->sun_path, salen);

     return addr;

 }

 #endif /* WIN32 */