From c8ecaea34f03b8ddda7d2b41b0d6f397469c8959 Mon Sep 17 00:00:00 2001

From: Eric Blake <eblake@redhat.com>

Date: Wed, 10 Jun 2020 18:32:02 -0400

Subject: [PATCH 2/2] block: Call attention to truncation of long NBD exports

RH-Author: Eric Blake <eblake@redhat.com>

Message-id: <20200610183202.3780750-3-eblake@redhat.com>

Patchwork-id: 97495

O-Subject: [RHEL-AV-8.2.1 qemu-kvm PATCH 2/2] block: Call attention to truncation of long NBD exports

Bugzilla: 1845384

RH-Acked-by: Sergio Lopez Pascual <slp@redhat.com>

RH-Acked-by: Max Reitz <mreitz@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Commit 93676c88 relaxed our NBD client code to request export names up

to the NBD protocol maximum of 4096 bytes without NUL terminator, even

though the block layer can't store anything longer than 4096 bytes

including NUL terminator for display to the user.  Since this means

there are some export names where we have to truncate things, we can

at least try to make the truncation a bit more obvious for the user.

Note that in spite of the truncated display name, we can still

communicate with an NBD server using such a long export name; this was

deemed nicer than refusing to even connect to such a server (since the

server may not be under our control, and since determining our actual

length limits gets tricky when nbd://host:port/export and

nbd+unix:///export?socket=/path are themselves variable-length

expansions beyond the export name but count towards the block layer

name length).

Reported-by: Xueqiang Wei <xuwei@redhat.com>

Fixes: https://bugzilla.redhat.com/1843684

Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Message-Id: <20200610163741.3745251-3-eblake@redhat.com>

(cherry picked from commit 5c86bdf1208916ece0b87e1151c9b48ee54faa3e)

Signed-off-by: Eric Blake <eblake@redhat.com>

Signed-off-by: Eduardo Lima (Etrunko) <etrunko@redhat.com>

---

 block.c     |  7 +++++--

 block/nbd.c | 21 +++++++++++++--------

 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/block.c b/block.c

index 12c8941879..57740d312e 100644

--- a/block.c

+++ b/block.c

@@ -6683,8 +6683,11 @@ void bdrv_refresh_filename(BlockDriverState *bs)

         pstrcpy(bs->filename, sizeof(bs->filename), bs->exact_filename);

     } else {

         QString *json = qobject_to_json(QOBJECT(bs->full_open_options));

-        snprintf(bs->filename, sizeof(bs->filename), "json:%s",

-                 qstring_get_str(json));

+        if (snprintf(bs->filename, sizeof(bs->filename), "json:%s",

+                     qstring_get_str(json)) >= sizeof(bs->filename)) {

+            /* Give user a hint if we truncated things. */

+            strcpy(bs->filename + sizeof(bs->filename) - 4, "...");

+        }

         qobject_unref(json);

     }

 }

diff --git a/block/nbd.c b/block/nbd.c

index 927915d93d..5bb154017d 100644

--- a/block/nbd.c

+++ b/block/nbd.c

@@ -1978,6 +1978,7 @@ static void nbd_refresh_filename(BlockDriverState *bs)

 {

     BDRVNBDState *s = bs->opaque;

     const char *host = NULL, *port = NULL, *path = NULL;

+    size_t len = 0;

     if (s->saddr->type == SOCKET_ADDRESS_TYPE_INET) {

         const InetSocketAddress *inet = &s->saddr->u.inet;

@@ -1990,17 +1991,21 @@ static void nbd_refresh_filename(BlockDriverState *bs)

     } /* else can't represent as pseudo-filename */

     if (path && s->export) {

-        snprintf(bs->exact_filename, sizeof(bs->exact_filename),

-                 "nbd+unix:///%s?socket=%s", s->export, path);

+        len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),

+                       "nbd+unix:///%s?socket=%s", s->export, path);

     } else if (path && !s->export) {

-        snprintf(bs->exact_filename, sizeof(bs->exact_filename),

-                 "nbd+unix://?socket=%s", path);

+        len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),

+                       "nbd+unix://?socket=%s", path);

     } else if (host && s->export) {

-        snprintf(bs->exact_filename, sizeof(bs->exact_filename),

-                 "nbd://%s:%s/%s", host, port, s->export);

+        len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),

+                       "nbd://%s:%s/%s", host, port, s->export);

     } else if (host && !s->export) {

-        snprintf(bs->exact_filename, sizeof(bs->exact_filename),

-                 "nbd://%s:%s", host, port);

+        len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),

+                       "nbd://%s:%s", host, port);

+    }

+    if (len > sizeof(bs->exact_filename)) {

+        /* Name is too long to represent exactly, so leave it empty. */

+        bs->exact_filename[0] = '\0';

     }

 }

-- 

2.27.0