Fix assertion in ext-mode BLOCK_STATUS (CVE-2023-5871)

(cherry picked from commit 267af1b608)

0001-generator-Fix-assertion-in-ext-mode-BLOCK_STATUS-CVE.patch

@@ -0,0 +1,86 @@
+From 177308adb17e81fce7c0f2b2fcf655c5c0b6a4d6 Mon Sep 17 00:00:00 2001
+From: Eric Blake <eblake@redhat.com>
+Date: Mon, 30 Oct 2023 12:50:53 -0500
+Subject: [PATCH] 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>
+---
+ generator/states-reply-chunk.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/generator/states-reply-chunk.c b/generator/states-reply-chunk.c
+index 5a31c19..8ab7e8b 100644
+--- a/generator/states-reply-chunk.c
++++ b/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;
+         }
+       }
+ 
+-- 
+2.41.0
+

libnbd.spec

@@ -8,8 +8,8 @@
 %global source_directory 1.18-stable
 
 Name:           libnbd
-Version:        1.18.0
-Release:        1%{?dist}
+Version:        1.18.1
+Release:        2%{?dist}
 Summary:        NBD client library in userspace
 
 License:        LGPL-2.0-or-later AND BSD-3-Clause
@@ -25,6 +25,9 @@ Source2:       libguestfs.keyring
 # Maintainer script which helps with handling patches.
 Source3:        copy-patches.sh
 
+# CVE-2023-5871
+Patch:          0001-generator-Fix-assertion-in-ext-mode-BLOCK_STATUS-CVE.patch
+
 %if 0%{patches_touch_autotools}
 BuildRequires: autoconf, automake, libtool
 %endif
@@ -375,8 +378,14 @@ make %{?_smp_mflags} check || {
 
 
 %changelog
+* Tue Oct 31 2023 Richard W.M. Jones <rjones@redhat.com> - 1.18.1-2
+- Fix assertion in ext-mode BLOCK_STATUS (CVE-2023-5871)
+
+* Mon Oct 23 2023 Richard W.M. Jones <rjones@redhat.com> - 1.18.1-1
+- New upstream stable version 1.18.1
+
 * Wed Sep 27 2023 Richard W.M. Jones <rjones@redhat.com> - 1.18.0-1
-- New upstream development version 1.18.0
+- New upstream stable version 1.18.0
 
 * Fri Sep 08 2023 Richard W.M. Jones <rjones@redhat.com> - 1.17.5-1
 - New upstream development version 1.17.5

sources

@@ -1,2 +1,2 @@
-SHA512 (libnbd-1.18.0.tar.gz) = e0dc41ce8cae8d6c8efd55ad560b847dd829ad355cd67e4f682ac2ad145f3ced8ea42650ce1b2cd562a1f6f8cf05680ff2e1a5bdf5b4e5f8237b1fb8ec132a3a
-SHA512 (libnbd-1.18.0.tar.gz.sig) = a506add984fddb12bb073947cf5ef6f798c6db6aae521aced778b03d7feb0227a4cf5bc346d68ada3e3da47b533cdcfd9c4470fddf61bfa82ed148d862b5ec82
+SHA512 (libnbd-1.18.1.tar.gz) = f4262666be55d580550e053355f14f80d352bf869ae7241e9fa032a9b5cd9e027eb89a536871c1206422413fc7ed745da7d612b3e1413f76ec17168705fbf12c
+SHA512 (libnbd-1.18.1.tar.gz.sig) = 57798aa8b8c0973c0e13f431a6735e13a5aa546190e5de9cb43f78d54c5438df70bdf6e875282a3c4221c222a1517c64bb311e769f7c1a3e61d5b1a4e7f75e2d