[PATCH v2] udf: validate extent partition references in udf_current_aext()

[Kyle Zeng <kylebot@openai.com>]

Long allocation descriptors carry an on-disk
extLocation.partitionReferenceNum. udf_current_aext() copies that value
into a kernel_lb_addr and returns it to several consumers.

If the partition reference is outside s_partitions, callers can later
index s_partmaps out of bounds. The truncate/free path can pass such an
extent to udf_free_blocks(), where the invalid partition reference
causes a slab out-of-bounds read.

Validate eloc->partitionReferenceNum in udf_current_aext() before
returning a decoded extent. This rejects invalid file extents and
indirect allocation descriptor extents in the common parser, so callers
do not need to duplicate the partition-map bounds check.

Assisted-by: Codex:gpt-5.5
Signed-off-by: Kyle Zeng <kylebot@openai.com>
---
 fs/udf/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 67bcf83..3a65b95 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -2151,6 +2151,7 @@ void udf_write_aext(struct inode *inode, struct extent_position *epos,
 	struct short_ad *sad;
 	struct long_ad *lad;
 	struct udf_inode_info *iinfo = UDF_I(inode);
+	struct udf_sb_info *sbi = UDF_SB(inode->i_sb);
 
 	if (!epos->bh)
 		ptr = iinfo->i_data + epos->offset -
@@ -2299,6 +2300,12 @@ int udf_current_aext(struct inode *inode, struct extent_position *epos,
 		return -EINVAL;
 	}
 
+	if (eloc->partitionReferenceNum >= sbi->s_partitions) {
+		udf_debug("invalid partition reference %u (partitions %u)\n",
+			  eloc->partitionReferenceNum, sbi->s_partitions);
+		return -EFSCORRUPTED;
+	}
+
 	return 1;
 }
 
-- 
2.54.0