udf: Allocate name buffer in directory iterator on heap

Currently we allocate name buffer in directory iterators (struct
udf_fileident_iter) on stack. These structures are relatively large
(some 360 bytes on 64-bit architectures). For udf_rename() which needs
to keep three of these structures in parallel the stack usage becomes
rather heavy - 1536 bytes in total. Allocate the name buffer in the
iterator from heap to avoid excessive stack usage.

Link: https://lore.kernel.org/all/202212200558.lK9x1KW0-lkp@intel.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/directory.c

@@ -248,9 +248,14 @@ int udf_fiiter_init(struct udf_fileident_iter *iter, struct inode *dir,
 	iter->elen = 0;
 	iter->epos.bh = NULL;
 	iter->name = NULL;
+	iter->namebuf = kmalloc(UDF_NAME_LEN_CS0, GFP_KERNEL);
+	if (!iter->namebuf)
+		return -ENOMEM;
 
-	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB)
-		return udf_copy_fi(iter);
+	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
+		err = udf_copy_fi(iter);
+		goto out;
+	}
 
 	if (inode_bmap(dir, iter->pos >> dir->i_blkbits, &iter->epos,
 		       &iter->eloc, &iter->elen, &iter->loffset) !=
@@ -260,17 +265,17 @@ int udf_fiiter_init(struct udf_fileident_iter *iter, struct inode *dir,
 		udf_err(dir->i_sb,
 			"position %llu not allocated in directory (ino %lu)\n",
 			(unsigned long long)pos, dir->i_ino);
-		return -EFSCORRUPTED;
+		err = -EFSCORRUPTED;
+		goto out;
 	}
 	err = udf_fiiter_load_bhs(iter);
 	if (err < 0)
-		return err;
+		goto out;
 	err = udf_copy_fi(iter);
-	if (err < 0) {
+out:
+	if (err < 0)
 		udf_fiiter_release(iter);
 	return err;
-	}
-	return 0;
 }
 
 int udf_fiiter_advance(struct udf_fileident_iter *iter)
@@ -307,6 +312,8 @@ void udf_fiiter_release(struct udf_fileident_iter *iter)
 	brelse(iter->bh[0]);
 	brelse(iter->bh[1]);
 	iter->bh[0] = iter->bh[1] = NULL;
+	kfree(iter->namebuf);
+	iter->namebuf = NULL;
 }
 
 static void udf_copy_to_bufs(void *buf1, int len1, void *buf2, int len2,

fs/udf/udfdecl.h

@@ -99,7 +99,7 @@ struct udf_fileident_iter {
 	struct extent_position epos;	/* Position after the above extent */
 	struct fileIdentDesc fi;	/* Copied directory entry */
 	uint8_t *name;			/* Pointer to entry name */
-	uint8_t namebuf[UDF_NAME_LEN_CS0]; /* Storage for entry name in case
+	uint8_t *namebuf;		/* Storage for entry name in case
 					 * the name is split between two blocks
 					 */
 };