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Accepting request 1125731 from Virtualization

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- Fix assertion in ext-mode BLOCK_STATUS, CVE-2023-5871
  4451e5b6-CVE-2023-5871.patch
  bsc#1216769

OBS-URL: https://build.opensuse.org/request/show/1125731
OBS-URL: https://build.opensuse.org/package/show/openSUSE:Factory/libnbd?expand=0&rev=14
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Ana Guerrero 2023-11-14 20:42:25 +00:00 committed by Git OBS Bridge
commit 5fa83b5ca0
3 changed files with 90 additions and 0 deletions
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4451e5b6-CVE-2023-5871.patch Normal file
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commit 4451e5b61ca07771ceef3e012223779e7a0c7701
Author: Eric Blake <eblake@redhat.com>
Date: Mon Oct 30 12:50:53 2023 -0500
generator: Fix assertion in ext-mode BLOCK_STATUS, CVE-2023-5871
Another round of fuzz testing revealed that when a server negotiates
extended headers and replies with a 64-bit flag value where the client
used the 32-bit API command, we were correctly flagging the server's
response as being an EOVERFLOW condition, but then immediately failing
in an assertion failure instead of reporting it to the application.
The following one-byte change to qemu.git at commit fd9a38fd43 allows
the creation of an intentionally malicious server:
| diff --git i/nbd/server.c w/nbd/server.c
| index 859c163d19f..32e1e771a95 100644
| --- i/nbd/server.c
| +++ w/nbd/server.c
| @@ -2178,7 +2178,7 @@ static void nbd_extent_array_convert_to_be(NBDExtentArray *ea)
|
| for (i = 0; i < ea->count; i++) {
| ea->extents[i].length = cpu_to_be64(ea->extents[i].length);
| - ea->extents[i].flags = cpu_to_be64(ea->extents[i].flags);
| + ea->extents[i].flags = ~cpu_to_be64(ea->extents[i].flags);
| }
| }
and can then be detected with the following command line:
$ nbdsh -c - <<\EOF
> def f(a,b,c,d):
> pass
>
> h.connect_systemd_socket_activation(["/path/to/bad/qemu-nbd",
> "-r", "-f", "raw", "TODO"])
> h.block_staus(h.get_size(), 0, f)
> EOF
nbdsh: generator/states-reply-chunk.c:626: enter_STATE_REPLY_CHUNK_REPLY_RECV_BS_ENTRIES: Assertion `(len | flags) <= UINT32_MAX' failed.
Aborted (core dumped)
whereas a fixed libnbd will give:
nbdsh: command line script failed: nbd_block_status: block-status: command failed: Value too large for defined data type
We can either relax the assertion (by changing to 'assert ((len |
flags) <= UINT32_MAX || cmd->error)'), or intentionally truncate flags
to make the existing assertion reliable. This patch goes with the
latter approach.
Sadly, this crash is possible in all existing 1.18.x stable releases,
if they were built with assertions enabled (most distros do this by
default), meaning a malicious server has an easy way to cause a Denial
of Service attack by triggering the assertion failure in vulnerable
clients, so we have assigned this CVE-2023-5871. Mitigating factors:
the crash only happens for a server that sends a 64-bit status block
reply (no known production servers do so; qemu 8.2 will be the first
known server to support extended headers, but it is not yet released);
and as usual, a client can use TLS to guarantee it is connecting only
to a known-safe server. If libnbd is compiled without assertions,
there is no crash or other mistaken behavior; and when assertions are
enabled, the attacker cannot accomplish anything more than a denial of
service.
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Fixes: 20dadb0e10 ("generator: Prepare for extent64 callback", v1.17.4)
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit 177308adb17e81fce7c0f2b2fcf655c5c0b6a4d6)
Signed-off-by: Eric Blake <eblake@redhat.com>
Index: libnbd-1.18.1/generator/states-reply-chunk.c
===================================================================
--- libnbd-1.18.1.orig/generator/states-reply-chunk.c
+++ libnbd-1.18.1/generator/states-reply-chunk.c
@@ -600,6 +600,7 @@ STATE_MACHINE {
break; /* Skip this and later extents; we already made progress */
/* Expose this extent as an error; we made no progress */
cmd->error = cmd->error ? : EOVERFLOW;
+ flags = (uint32_t)flags;
}
}

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libnbd.changes
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@ -1,3 +1,10 @@
-------------------------------------------------------------------
Mon Nov 13 21:15:40 UTC 2023 - James Fehlig <jfehlig@suse.com>
- Fix assertion in ext-mode BLOCK_STATUS, CVE-2023-5871
4451e5b6-CVE-2023-5871.patch
bsc#1216769
-------------------------------------------------------------------
Wed Oct 25 19:29:55 UTC 2023 - jfehlig@suse.com

1
libnbd.spec
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@ -25,6 +25,7 @@ Summary: NBD client library in userspace
License: LGPL-2.1-or-later
URL: https://gitlab.com/nbdkit/libnbd
Source0: %{name}-%{version}.tar.bz2
Patch0: 4451e5b6-CVE-2023-5871.patch
BuildRequires: autoconf
BuildRequires: automake
BuildRequires: fdupes