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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722627733; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zujWLanYU65hRJrPq3mrZmUXtKznUN/BGwM9MRtRTtE=; b=WnceGgKZhlG25Pw9rVSme6oBxm6cDypgV38TLyZpUtUV2A7cCLmDNGakt+STBsWQlzYeby sxeiUoth8KgaYqaH7UOWgA8/X+rt3X9caox73NbUcEaTEGfXxhIFqJ86lU/FxzQSnto/im 5LzIjRhRCbpm90FBf8Lo7RZNhtltRwE= X-MC-Unique: R71nrcNcMwalGvZc5B7s5A-1 From: Eric Blake To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, rjones@redhat.com, Vladimir Sementsov-Ogievskiy Subject: [PATCH 2/2] qemu-img: CVE-XXX Sanitize untrusted output from NBD server Date: Fri, 2 Aug 2024 14:26:06 -0500 Message-ID: <20240802194156.2131519-6-eblake@redhat.com> In-Reply-To: <20240802194156.2131519-4-eblake@redhat.com> References: <20240802194156.2131519-4-eblake@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" Error messages from an NBD server must be treated as untrusted; a malicious server can inject escape sequences to try and trigger RCE flaws via escape sequences to whatever terminal happens to be running qemu-img. The easiest solution is to sanitize the output with the same code we use to produce sanitized (pseudo-)JSON over QMP. Rich Jones originally pointed this flaw out at: https://lists.libguestfs.org/archives/list/guestfs@lists.libguestfs.org/thr= ead/2NXA23G2V3HPWJYAO726PLNBEAAEUJAU/ With this patch, and a malicious server run with nbdkit 1.40 as: $ nbdkit --log=3Dnull eval open=3D' printf \ "EPERM x\\r mess up the output \e[31mmess up the output\e[m mess up" >&2;= \ exit 1 ' get_size=3D' echo 0 ' --run 'qemu-img info "$uri"' we now get: qemu-img: Could not open 'nbd://localhost': Requested export not available server reported: /tmp/nbdkitOZHOKB/open: x\r mess up the output \u001B[31mm= ess up the output\u001B[m mess up instead of an attempt to hide the name of the Unix socket and forcing the terminal to render part of the text red. Note that I did _not_ sanitize the string being sent through trace-events in trace_nbd_server_error_msg; this is because I assume that our trace engines already treat all string strings as untrusted input and apply their own escaping as needed. Reported-by: "Richard W.M. Jones" Signed-off-by: Eric Blake Reviewed-by: Daniel P. Berrang=C3=A9 Reviewed-by: Philippe Mathieu-Daud=C3=A9 Reviewed-by: Richard W.M. Jones --- If my assumption about allowing raw escape bytes through to trace_ calls is wrong (such as when tracing to stderr), let me know. That's a much bigger audit to determine which trace points, if any, should sanitize data before tracing, and/or change the trace engines to sanitize all strings (with possible knock-on effects if trace output changes unexpectedly for a tool expecting something unsanitized). --- nbd/client.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/nbd/client.c b/nbd/client.c index c89c7504673..baa20d10d69 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -23,6 +23,7 @@ #include "trace.h" #include "nbd-internal.h" #include "qemu/cutils.h" +#include "qemu/unicode.h" /* Definitions for opaque data types */ @@ -230,7 +231,9 @@ static int nbd_handle_reply_err(QIOChannel *ioc, NBDOpt= ionReply *reply, } if (msg) { - error_append_hint(errp, "server reported: %s\n", msg); + g_autoptr(GString) buf =3D g_string_sized_new(reply->length); + mod_utf8_sanitize(buf, msg); + error_append_hint(errp, "server reported: %s\n", buf->str); } err: --=20 2.45.2