When reading with `read_cluster` we get the `mapping` with
`find_mapping_for_cluster` and then we call `open_file` for this
mapping.
The issue appear when its the same file, but a second cluster that is
not immediately after it, imagine clusters `500 -> 503`, this will give
us 2 mappings one has the range `500..501` and another `503..504`, both
point to the same file, but different offsets.

When we don't open the file since the path is the same, we won't assign
`s->current_mapping` and thus accessing way out of bound of the file.

From our example above, after `open_file` (that didn't open anything) we
will get the offset into the file with
`s->cluster_size*(cluster_num-s->current_mapping->begin)`, which will
give us `0x2000 * (504-500)`, which is out of bound for this mapping and
will produce some issues.

Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
---
 block/vvfat.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index cb3ab81e29..87165abc26 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1360,15 +1360,22 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
 {
     if(!mapping)
         return -1;
+    int new_path = 1;
     if(!s->current_mapping ||
-            strcmp(s->current_mapping->path,mapping->path)) {
-        /* open file */
-        int fd = qemu_open_old(mapping->path,
+            s->current_mapping->first_mapping_index!=mapping->first_mapping_index ||
+            (new_path = strcmp(s->current_mapping->path,mapping->path))) {
+
+        if (new_path) {
+            /* open file */
+            int fd = qemu_open_old(mapping->path,
                                O_RDONLY | O_BINARY | O_LARGEFILE);
-        if(fd<0)
-            return -1;
-        vvfat_close_current_file(s);
-        s->current_fd = fd;
+            if(fd<0)
+                return -1;
+            vvfat_close_current_file(s);
+
+            s->current_fd = fd;
+        }
+        assert(s->current_fd);
         s->current_mapping = mapping;
     }
     return 0;
-- 
2.44.0

I noticed the issue in the commit message 'ffvat' should be 'vvfat',
I'll fix it in the next version.

On Thu, Mar 28, 2024 at 04:11:27AM +0800, Amjad Alsharafi wrote:
> When reading with `read_cluster` we get the `mapping` with
> `find_mapping_for_cluster` and then we call `open_file` for this
> mapping.
> The issue appear when its the same file, but a second cluster that is
> not immediately after it, imagine clusters `500 -> 503`, this will give
> us 2 mappings one has the range `500..501` and another `503..504`, both
> point to the same file, but different offsets.
> 
> When we don't open the file since the path is the same, we won't assign
> `s->current_mapping` and thus accessing way out of bound of the file.
> 
> From our example above, after `open_file` (that didn't open anything) we
> will get the offset into the file with
> `s->cluster_size*(cluster_num-s->current_mapping->begin)`, which will
> give us `0x2000 * (504-500)`, which is out of bound for this mapping and
> will produce some issues.
> 
> Signed-off-by: Amjad Alsharafi <amjadsharafi10@gmail.com>
> ---
>  block/vvfat.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/block/vvfat.c b/block/vvfat.c
> index cb3ab81e29..87165abc26 100644
> --- a/block/vvfat.c
> +++ b/block/vvfat.c
> @@ -1360,15 +1360,22 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
>  {
>      if(!mapping)
>          return -1;
> +    int new_path = 1;
>      if(!s->current_mapping ||
> -            strcmp(s->current_mapping->path,mapping->path)) {
> -        /* open file */
> -        int fd = qemu_open_old(mapping->path,
> +            s->current_mapping->first_mapping_index!=mapping->first_mapping_index ||
> +            (new_path = strcmp(s->current_mapping->path,mapping->path))) {
> +
> +        if (new_path) {
> +            /* open file */
> +            int fd = qemu_open_old(mapping->path,
>                                 O_RDONLY | O_BINARY | O_LARGEFILE);
> -        if(fd<0)
> -            return -1;
> -        vvfat_close_current_file(s);
> -        s->current_fd = fd;
> +            if(fd<0)
> +                return -1;
> +            vvfat_close_current_file(s);
> +
> +            s->current_fd = fd;
> +        }
> +        assert(s->current_fd);
>          s->current_mapping = mapping;
>      }
>      return 0;
> -- 
> 2.44.0
>