[PATCH 5.15.y] udf: fix partition descriptor append bookkeeping

[Sasha Levin <sashal@kernel.org>]

From: Seohyeon Maeng <bioloidgp@gmail.com>

[ Upstream commit 08841b06fa64d8edbd1a21ca6e613420c90cc4b8 ]

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>
Link: https://patch.msgid.link/20260310081652.21220-1-bioloidgp@gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
[ replaced kzalloc_objs() helper with equivalent kcalloc() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 69e4f00ce791b..f58a48fc0ade0 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -1658,8 +1658,9 @@ 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 new_size;
 
+		new_size = data->num_part_descs + PART_DESC_ALLOC_STEP;
 		new_loc = kcalloc(new_size, sizeof(*new_loc), GFP_KERNEL);
 		if (!new_loc)
 			return ERR_PTR(-ENOMEM);
@@ -1669,6 +1670,7 @@ 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);
 }
 
-- 
2.53.0