block/vmdk: Report failures in vmdk_read_cid()

Message ID 20170709170614.24967-1-peter.maydell@linaro.org
State Superseded
Headers show

Commit Message

Peter Maydell July 9, 2017, 5:06 p.m.
The function vmdk_read_cid() can fail if the read on the underlying
block device fails, or if there's a format error in the VMDK file.
However its API doesn't provide a mechanism to report these errors,
and in some cases we were returning a CID of 0 and in some cases a
CID of 0xffffffff, either of which might potentially be valid values.

Change the function to return 0 on success or a negative errno, and
return the CID via a uint32_t* argument. Update the callsites to
handle and propagate the error appropriately.

This fixes in passing a Coverity-spotted issue (CID 1350038) where
we weren't checking the return value from sscanf().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

---
 block/vmdk.c | 44 ++++++++++++++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 12 deletions(-)

-- 
2.11.0

Comments

Fam Zheng July 10, 2017, 1:58 a.m. | #1
On Sun, 07/09 18:06, Peter Maydell wrote:
> The function vmdk_read_cid() can fail if the read on the underlying

> block device fails, or if there's a format error in the VMDK file.

> However its API doesn't provide a mechanism to report these errors,

> and in some cases we were returning a CID of 0 and in some cases a

> CID of 0xffffffff, either of which might potentially be valid values.

> 

> Change the function to return 0 on success or a negative errno, and

> return the CID via a uint32_t* argument. Update the callsites to

> handle and propagate the error appropriately.

> 

> This fixes in passing a Coverity-spotted issue (CID 1350038) where

> we weren't checking the return value from sscanf().

> 

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>



Reviewed-by: Fam Zheng <famz@redhat.com>
Kevin Wolf July 13, 2017, 12:09 p.m. | #2
Am 10.07.2017 um 03:58 hat Fam Zheng geschrieben:
> On Sun, 07/09 18:06, Peter Maydell wrote:

> > The function vmdk_read_cid() can fail if the read on the underlying

> > block device fails, or if there's a format error in the VMDK file.

> > However its API doesn't provide a mechanism to report these errors,

> > and in some cases we were returning a CID of 0 and in some cases a

> > CID of 0xffffffff, either of which might potentially be valid values.

> > 

> > Change the function to return 0 on success or a negative errno, and

> > return the CID via a uint32_t* argument. Update the callsites to

> > handle and propagate the error appropriately.

> > 

> > This fixes in passing a Coverity-spotted issue (CID 1350038) where

> > we weren't checking the return value from sscanf().

> > 

> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

> 

> Reviewed-by: Fam Zheng <famz@redhat.com>


Thanks, applied to the block branch.

Kevin
Kevin Wolf July 28, 2017, 12:54 p.m. | #3
Am 09.07.2017 um 19:06 hat Peter Maydell geschrieben:
> The function vmdk_read_cid() can fail if the read on the underlying

> block device fails, or if there's a format error in the VMDK file.

> However its API doesn't provide a mechanism to report these errors,

> and in some cases we were returning a CID of 0 and in some cases a

> CID of 0xffffffff, either of which might potentially be valid values.

> 

> Change the function to return 0 on success or a negative errno, and

> return the CID via a uint32_t* argument. Update the callsites to

> handle and propagate the error appropriately.

> 

> This fixes in passing a Coverity-spotted issue (CID 1350038) where

> we weren't checking the return value from sscanf().

> 

> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>


Fam, this is the commit that introduced the qemu-iotests 059 failure for
vmdk. I think what's happening is that we use an image produced by a
fuzzer, and with the additional checks introduced in this patch, we now
fail earlier and don't test the condition any more that we wanted to
test.

So do we need a new version of sample_images/afl9.vmdk.bz2 that has a
valid CID?

Kevin

Patch

diff --git a/block/vmdk.c b/block/vmdk.c
index 55581b03fe..0c9949fc0c 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -242,10 +242,11 @@  static void vmdk_free_last_extent(BlockDriverState *bs)
     s->extents = g_renew(VmdkExtent, s->extents, s->num_extents);
 }
 
-static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)
+/* Return -ve errno, or 0 on success and write CID into *pcid. */
+static int vmdk_read_cid(BlockDriverState *bs, int parent, uint32_t *pcid)
 {
     char *desc;
-    uint32_t cid = 0xffffffff;
+    uint32_t cid;
     const char *p_name, *cid_str;
     size_t cid_str_size;
     BDRVVmdkState *s = bs->opaque;
@@ -254,8 +255,7 @@  static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)
     desc = g_malloc0(DESC_SIZE);
     ret = bdrv_pread(bs->file, s->desc_offset, desc, DESC_SIZE);
     if (ret < 0) {
-        g_free(desc);
-        return 0;
+        goto out;
     }
 
     if (parent) {
@@ -268,13 +268,21 @@  static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)
 
     desc[DESC_SIZE - 1] = '\0';
     p_name = strstr(desc, cid_str);
-    if (p_name != NULL) {
-        p_name += cid_str_size;
-        sscanf(p_name, "%" SCNx32, &cid);
+    if (p_name == NULL) {
+        ret = -EINVAL;
+        goto out;
     }
+    p_name += cid_str_size;
+    if (sscanf(p_name, "%" SCNx32, &cid) != 1) {
+        ret = -EINVAL;
+        goto out;
+    }
+    *pcid = cid;
+    ret = 0;
 
+out:
     g_free(desc);
-    return cid;
+    return ret;
 }
 
 static int vmdk_write_cid(BlockDriverState *bs, uint32_t cid)
@@ -322,7 +330,10 @@  static int vmdk_is_cid_valid(BlockDriverState *bs)
     if (!s->cid_checked && bs->backing) {
         BlockDriverState *p_bs = bs->backing->bs;
 
-        cur_pcid = vmdk_read_cid(p_bs, 0);
+        if (vmdk_read_cid(p_bs, 0, &cur_pcid) != 0) {
+            /* read failure: report as not valid */
+            return 0;
+        }
         if (s->parent_cid != cur_pcid) {
             /* CID not valid */
             return 0;
@@ -975,8 +986,14 @@  static int vmdk_open(BlockDriverState *bs, QDict *options, int flags,
     if (ret) {
         goto fail;
     }
-    s->cid = vmdk_read_cid(bs, 0);
-    s->parent_cid = vmdk_read_cid(bs, 1);
+    ret = vmdk_read_cid(bs, 0, &s->cid);
+    if (ret) {
+        goto fail;
+    }
+    ret = vmdk_read_cid(bs, 1, &s->parent_cid);
+    if (ret) {
+        goto fail;
+    }
     qemu_co_mutex_init(&s->lock);
 
     /* Disable migration when VMDK images are used */
@@ -2007,8 +2024,11 @@  static int vmdk_create(const char *filename, QemuOpts *opts, Error **errp)
             ret = -EINVAL;
             goto exit;
         }
-        parent_cid = vmdk_read_cid(blk_bs(blk), 0);
+        ret = vmdk_read_cid(blk_bs(blk), 0, &parent_cid);
         blk_unref(blk);
+        if (ret) {
+            goto exit;
+        }
         snprintf(parent_desc_line, BUF_SIZE,
                 "parentFileNameHint=\"%s\"", backing_file);
     }