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qemu: fix CVE-2020-10761
(From OE-Core rev: 5509c7247fb44c8fb98298f2b309cc1a87b07f14) Signed-off-by: Lee Chee Yang <chee.yang.lee@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Lee Chee Yang
committed by
Richard Purdie
Richard Purdie
parent
771122ebeb
commit
43345b55b7
@@ -31,6 +31,7 @@ SRC_URI = "https://download.qemu.org/${BPN}-${PV}.tar.xz \
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file://0001-qemu-Do-not-include-file-if-not-exists.patch \
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file://CVE-2020-13361.patch \
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file://find_datadir.patch \
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file://CVE-2020-10761.patch \
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"
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UPSTREAM_CHECK_REGEX = "qemu-(?P<pver>\d+(\.\d+)+)\.tar"
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@@ -0,0 +1,151 @@
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From 5c4fe018c025740fef4a0a4421e8162db0c3eefd Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Mon, 8 Jun 2020 13:26:37 -0500
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Subject: [PATCH] nbd/server: Avoid long error message assertions
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CVE-2020-10761
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Ever since commit 36683283 (v2.8), the server code asserts that error
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strings sent to the client are well-formed per the protocol by not
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exceeding the maximum string length of 4096. At the time the server
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first started sending error messages, the assertion could not be
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triggered, because messages were completely under our control.
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However, over the years, we have added latent scenarios where a client
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could trigger the server to attempt an error message that would
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include the client's information if it passed other checks first:
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- requesting NBD_OPT_INFO/GO on an export name that is not present
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(commit 0cfae925 in v2.12 echoes the name)
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- requesting NBD_OPT_LIST/SET_META_CONTEXT on an export name that is
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not present (commit e7b1948d in v2.12 echoes the name)
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At the time, those were still safe because we flagged names larger
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than 256 bytes with a different message; but that changed in commit
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93676c88 (v4.2) when we raised the name limit to 4096 to match the NBD
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string limit. (That commit also failed to change the magic number
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4096 in nbd_negotiate_send_rep_err to the just-introduced named
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constant.) So with that commit, long client names appended to server
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text can now trigger the assertion, and thus be used as a denial of
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service attack against a server. As a mitigating factor, if the
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server requires TLS, the client cannot trigger the problematic paths
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unless it first supplies TLS credentials, and such trusted clients are
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less likely to try to intentionally crash the server.
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We may later want to further sanitize the user-supplied strings we
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place into our error messages, such as scrubbing out control
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characters, but that is less important to the CVE fix, so it can be a
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later patch to the new nbd_sanitize_name.
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Consideration was given to changing the assertion in
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nbd_negotiate_send_rep_verr to instead merely log a server error and
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truncate the message, to avoid leaving a latent path that could
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trigger a future CVE DoS on any new error message. However, this
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merely complicates the code for something that is already (correctly)
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flagging coding errors, and now that we are aware of the long message
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pitfall, we are less likely to introduce such errors in the future,
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which would make such error handling dead code.
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Reported-by: Xueqiang Wei <xuwei@redhat.com>
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CC: qemu-stable@nongnu.org
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Fixes: https://bugzilla.redhat.com/1843684 CVE-2020-10761
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Fixes: 93676c88d7
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Signed-off-by: Eric Blake <eblake@redhat.com>
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Message-Id: <20200610163741.3745251-2-eblake@redhat.com>
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Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Upstream-Status: Backport [https://github.com/qemu/qemu/commit/5c4fe018c025740fef4a0a4421e8162db0c3eefd]
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CVE: CVE-2020-10761
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Signed-off-by: Chee Yang Lee <chee.yang.lee@intel.com>
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---
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nbd/server.c | 23 ++++++++++++++++++++---
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tests/qemu-iotests/143 | 4 ++++
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tests/qemu-iotests/143.out | 2 ++
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3 files changed, 26 insertions(+), 3 deletions(-)
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diff --git a/nbd/server.c b/nbd/server.c
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index 02b1ed08014..20754e9ebc3 100644
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--- a/nbd/server.c
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+++ b/nbd/server.c
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@@ -217,7 +217,7 @@ nbd_negotiate_send_rep_verr(NBDClient *client, uint32_t type,
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msg = g_strdup_vprintf(fmt, va);
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len = strlen(msg);
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- assert(len < 4096);
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+ assert(len < NBD_MAX_STRING_SIZE);
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trace_nbd_negotiate_send_rep_err(msg);
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ret = nbd_negotiate_send_rep_len(client, type, len, errp);
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if (ret < 0) {
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@@ -231,6 +231,19 @@ nbd_negotiate_send_rep_verr(NBDClient *client, uint32_t type,
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return 0;
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}
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+/*
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+ * Return a malloc'd copy of @name suitable for use in an error reply.
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+ */
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+static char *
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+nbd_sanitize_name(const char *name)
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+{
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+ if (strnlen(name, 80) < 80) {
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+ return g_strdup(name);
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+ }
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+ /* XXX Should we also try to sanitize any control characters? */
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+ return g_strdup_printf("%.80s...", name);
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+}
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+
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/* Send an error reply.
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* Return -errno on error, 0 on success. */
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static int GCC_FMT_ATTR(4, 5)
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@@ -595,9 +608,11 @@ static int nbd_negotiate_handle_info(NBDClient *client, Error **errp)
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exp = nbd_export_find(name);
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if (!exp) {
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+ g_autofree char *sane_name = nbd_sanitize_name(name);
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+
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return nbd_negotiate_send_rep_err(client, NBD_REP_ERR_UNKNOWN,
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errp, "export '%s' not present",
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- name);
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+ sane_name);
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}
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/* Don't bother sending NBD_INFO_NAME unless client requested it */
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@@ -995,8 +1010,10 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
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meta->exp = nbd_export_find(export_name);
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if (meta->exp == NULL) {
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+ g_autofree char *sane_name = nbd_sanitize_name(export_name);
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+
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return nbd_opt_drop(client, NBD_REP_ERR_UNKNOWN, errp,
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- "export '%s' not present", export_name);
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+ "export '%s' not present", sane_name);
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}
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ret = nbd_opt_read(client, &nb_queries, sizeof(nb_queries), errp);
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diff --git a/tests/qemu-iotests/143 b/tests/qemu-iotests/143
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index f649b361950..d2349903b1b 100755
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--- a/tests/qemu-iotests/143
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+++ b/tests/qemu-iotests/143
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@@ -58,6 +58,10 @@ _send_qemu_cmd $QEMU_HANDLE \
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$QEMU_IO_PROG -f raw -c quit \
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"nbd+unix:///no_such_export?socket=$SOCK_DIR/nbd" 2>&1 \
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| _filter_qemu_io | _filter_nbd
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+# Likewise, with longest possible name permitted in NBD protocol
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+$QEMU_IO_PROG -f raw -c quit \
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+ "nbd+unix:///$(printf %4096d 1 | tr ' ' a)?socket=$SOCK_DIR/nbd" 2>&1 \
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+ | _filter_qemu_io | _filter_nbd | sed 's/aaaa*aa/aa--aa/'
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_send_qemu_cmd $QEMU_HANDLE \
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"{ 'execute': 'quit' }" \
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diff --git a/tests/qemu-iotests/143.out b/tests/qemu-iotests/143.out
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index 1f4001c6013..fc9c0a761fa 100644
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--- a/tests/qemu-iotests/143.out
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+++ b/tests/qemu-iotests/143.out
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@@ -5,6 +5,8 @@ QA output created by 143
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{"return": {}}
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qemu-io: can't open device nbd+unix:///no_such_export?socket=SOCK_DIR/nbd: Requested export not available
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server reported: export 'no_such_export' not present
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+qemu-io: can't open device nbd+unix:///aa--aa1?socket=SOCK_DIR/nbd: Requested export not available
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+server reported: export 'aa--aa...' not present
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{ 'execute': 'quit' }
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{"return": {}}
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
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