[PATCH] udf: fix partition descriptor append bookkeeping

[PATCH] udf: fix partition descriptor append bookkeeping

[Seohyeon Maeng]

Mounting a crafted UDF image with repeated partition descriptors can
trigger a heap out-of-bounds write in part_descs_loc[].

handle_partition_descriptor() deduplicates entries by partition number,
but appended slots never record partnum. As a result duplicate
Partition Descriptors are appended repeatedly and num_part_descs keeps
growing.

Once the table is full, the growth path still sizes the allocation from
partnum even though inserts are indexed by num_part_descs. If partnum is
already aligned to PART_DESC_ALLOC_STEP, ALIGN(partnum, step) can keep
the old capacity and the next append writes past the end of the table.

Store partnum in the appended slot and size growth from the next append
count so deduplication and capacity tracking follow the same model.

Fixes: ee4af50ca94f ("udf: Fix mounting of Win7 created UDF filesystems")
Cc: stable@vger.kernel.org
Signed-off-by: Seohyeon Maeng <bioloidgp@gmail.com>
---
 fs/udf/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/udf/super.c b/fs/udf/super.c
index 27f463fd1d89..3c3c645de0bc 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -1694,7 +1694,8 @@ static struct udf_vds_record *handle_partition_descriptor(
 			return &(data->part_descs_loc[i].rec);
 	if (data->num_part_descs >= data->size_part_descs) {
 		struct part_desc_seq_scan_data *new_loc;
-		unsigned int new_size = ALIGN(partnum, PART_DESC_ALLOC_STEP);
+		unsigned int need = data->num_part_descs + 1;
+		unsigned int new_size = ALIGN(need, PART_DESC_ALLOC_STEP);
 
 		new_loc = kzalloc_objs(*new_loc, new_size);
 		if (!new_loc)
@@ -1705,6 +1706,7 @@ static struct udf_vds_record *handle_partition_descriptor(
 		data->part_descs_loc = new_loc;
 		data->size_part_descs = new_size;
 	}
+	data->part_descs_loc[data->num_part_descs].partnum = partnum;
 	return &(data->part_descs_loc[data->num_part_descs++].rec);
 }
 

base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
-- 
2.43.0

Re: [PATCH] udf: fix partition descriptor append bookkeeping

[Jan Kara]

On Tue 10-03-26 17:16:52, Seohyeon Maeng wrote:
> Mounting a crafted UDF image with repeated partition descriptors can
> trigger a heap out-of-bounds write in part_descs_loc[].
> 
> handle_partition_descriptor() deduplicates entries by partition number,
> but appended slots never record partnum. As a result duplicate
> Partition Descriptors are appended repeatedly and num_part_descs keeps
> growing.
> 
> Once the table is full, the growth path still sizes the allocation from
> partnum even though inserts are indexed by num_part_descs. If partnum is
> already aligned to PART_DESC_ALLOC_STEP, ALIGN(partnum, step) can keep
> the old capacity and the next append writes past the end of the table.
> 
> Store partnum in the appended slot and size growth from the next append
> count so deduplication and capacity tracking follow the same model.
> 
> Fixes: ee4af50ca94f ("udf: Fix mounting of Win7 created UDF filesystems")
> Cc: stable@vger.kernel.org
> Signed-off-by: Seohyeon Maeng <bioloidgp@gmail.com>

Thanks! I've merged the fix to my tree with a slight modification to set:

	new_size = data->num_part_descs + PART_DESC_ALLOC_STEP;

instead of the +1 and ALIGN() calls which were mostly pointless.

								Honza

> ---
>  fs/udf/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/udf/super.c b/fs/udf/super.c
> index 27f463fd1d89..3c3c645de0bc 100644
> --- a/fs/udf/super.c
> +++ b/fs/udf/super.c
> @@ -1694,7 +1694,8 @@ static struct udf_vds_record *handle_partition_descriptor(
>  			return &(data->part_descs_loc[i].rec);
>  	if (data->num_part_descs >= data->size_part_descs) {
>  		struct part_desc_seq_scan_data *new_loc;
> -		unsigned int new_size = ALIGN(partnum, PART_DESC_ALLOC_STEP);
> +		unsigned int need = data->num_part_descs + 1;
> +		unsigned int new_size = ALIGN(need, PART_DESC_ALLOC_STEP);
>  
>  		new_loc = kzalloc_objs(*new_loc, new_size);
>  		if (!new_loc)
> @@ -1705,6 +1706,7 @@ static struct udf_vds_record *handle_partition_descriptor(
>  		data->part_descs_loc = new_loc;
>  		data->size_part_descs = new_size;
>  	}
> +	data->part_descs_loc[data->num_part_descs].partnum = partnum;
>  	return &(data->part_descs_loc[data->num_part_descs++].rec);
>  }
>  
> 
> base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR