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Re: [PATCH v3 1/8] parallels: Out of image offset in BAT leads to image

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v3 1/8] parallels: Out of image offset in BAT leads to image inflation
Date: Wed, 17 Aug 2022 22:43:41 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1

On 8/17/22 22:27, Denis V. Lunev wrote:
On 17.08.2022 21:13, Vladimir Sementsov-Ogievskiy wrote:
On 8/15/22 12:02, Alexander Ivanov wrote:
data_end field in BDRVParallelsState is set to the biggest offset present
in BAT. If this offset is outside of the image, any further write will create
the cluster at this offset and/or the image will be truncated to this
offset on close. This is definitely not correct and should be fixed.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
v2: No change.
v3: Fix commit message.

  block/parallels.c | 17 +++++++++++++++++
  1 file changed, 17 insertions(+)

diff --git a/block/parallels.c b/block/parallels.c
index a229c06f25..a76cf9d993 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -732,6 +732,7 @@ static int parallels_open(BlockDriverState *bs, QDict 
*options, int flags,
      BDRVParallelsState *s = bs->opaque;
      ParallelsHeader ph;
      int ret, size, i;
+    int64_t file_size;
      QemuOpts *opts = NULL;
      Error *local_err = NULL;
      char *buf;
@@ -811,6 +812,22 @@ static int parallels_open(BlockDriverState *bs, QDict 
*options, int flags,
  +    file_size = bdrv_getlength(bs->file->bs);
+    if (file_size < 0) {
+        goto fail;
+    }
+    file_size >>= BDRV_SECTOR_BITS;
+    if (s->data_end > file_size) {
+        if (flags & BDRV_O_CHECK) {
+            s->data_end = file_size;

Hm. but with this, any further allocation may lead to twice-allocted clusters, as 
you just modify s->data_end, but havn't yet fixed the BAT entry.. It seems 
unsafe. Or what I miss?

if O_CHECK is specified, we are going to execute parallels_co_check which
will correctly handle this. In the other case (normal open) we will
face the error, which is pretty much correct under this logic.

Sounds like "s->data_end = file_size" is part of this handling and should be in 

Looking at it, seems more correct to recalculate s->data_end exactly after 
for-loop, which fixes out-of-image clusters. Also it would work better in case 
when we have leaked clusters at the end of file.

Otherwise, ideally, you should have comment at top of parallels_co_check(), 
that we must first fix out-of-image clusters, before doing any kind of 
allocation, because data_end is already tweaked.

I agree that patch should work as is.

+        } else {
+            error_setg(errp, "parallels: Offset in BAT is out of image");
+            ret = -EINVAL;
+            goto fail;
+        }
+    }
      if (le32_to_cpu(ph.inuse) == HEADER_INUSE_MAGIC) {
          /* Image was not closed correctly. The check is mandatory */
          s->header_unclean = true;

Best regards,

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