ext4: fix reading leftover inlined symlinks

Since commit 6493792d32 ("ext4: convert symlink external data block
mapping to bdev"), create new symlink with inline_data is not supported,
but it missing to handle the leftover inlined symlinks, which could
cause below error message and fail to read symlink.

 ls: cannot read symbolic link 'foo': Structure needs cleaning

 EXT4-fs error (device sda): ext4_map_blocks:605: inode #12: block
 2021161080: comm ls: lblock 0 mapped to illegal pblock 2021161080
 (length 1)

Fix this regression by adding ext4_read_inline_link(), which read the
inline data directly and convert it through a kmalloced buffer.

Fixes: 6493792d32 ("ext4: convert symlink external data block mapping to bdev")
Cc: stable@kernel.org
Reported-by: Torge Matthies <openglfreak@googlemail.com>
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Tested-by: Torge Matthies <openglfreak@googlemail.com>
Link: https://lore.kernel.org/r/20220630090100.2769490-1-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -3583,6 +3583,7 @@ extern struct buffer_head *ext4_get_first_inline_block(struct inode *inode,
 extern int ext4_inline_data_fiemap(struct inode *inode,
 				   struct fiemap_extent_info *fieinfo,
 				   int *has_inline, __u64 start, __u64 len);
+extern void *ext4_read_inline_link(struct inode *inode);
 
 struct iomap;
 extern int ext4_inline_data_iomap(struct inode *inode, struct iomap *iomap);

fs/ext4/inline.c

@@ -6,6 +6,7 @@
 
 #include <linux/iomap.h>
 #include <linux/fiemap.h>
+#include <linux/namei.h>
 #include <linux/iversion.h>
 #include <linux/sched/mm.h>
 
@@ -1588,6 +1589,35 @@ out:
 	return ret;
 }
 
+void *ext4_read_inline_link(struct inode *inode)
+{
+	struct ext4_iloc iloc;
+	int ret, inline_size;
+	void *link;
+
+	ret = ext4_get_inode_loc(inode, &iloc);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = -ENOMEM;
+	inline_size = ext4_get_inline_size(inode);
+	link = kmalloc(inline_size + 1, GFP_NOFS);
+	if (!link)
+		goto out;
+
+	ret = ext4_read_inline_data(inode, link, inline_size, &iloc);
+	if (ret < 0) {
+		kfree(link);
+		goto out;
+	}
+	nd_terminate_link(link, inode->i_size, ret);
+out:
+	if (ret < 0)
+		link = ERR_PTR(ret);
+	brelse(iloc.bh);
+	return link;
+}
+
 struct buffer_head *ext4_get_first_inline_block(struct inode *inode,
 					struct ext4_dir_entry_2 **parent_de,
 					int *retval)

fs/ext4/symlink.c

@@ -74,6 +74,21 @@ static const char *ext4_get_link(struct dentry *dentry, struct inode *inode,
 				 struct delayed_call *callback)
 {
 	struct buffer_head *bh;
+	char *inline_link;
+
+	/*
+	 * Create a new inlined symlink is not supported, just provide a
+	 * method to read the leftovers.
+	 */
+	if (ext4_has_inline_data(inode)) {
+		if (!dentry)
+			return ERR_PTR(-ECHILD);
+
+		inline_link = ext4_read_inline_link(inode);
+		if (!IS_ERR(inline_link))
+			set_delayed_call(callback, kfree_link, inline_link);
+		return inline_link;
+	}
 
 	if (!dentry) {
 		bh = ext4_getblk(NULL, inode, 0, EXT4_GET_BLOCKS_CACHED_NOWAIT);