linux-ext4 - [PATCH] ext4: Read inlined symlink targets using ext4_readpage

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Message-Id: <20220628033446.285207-1-openglfreak@googlemail.com>
Date:   Tue, 28 Jun 2022 05:34:46 +0200
From:   Torge Matthies <openglfreak@...glemail.com>
To:     linux-ext4@...r.kernel.org
Cc:     Torge Matthies <openglfreak@...glemail.com>
Subject: [PATCH] ext4: Read inlined symlink targets using ext4_readpage_inline.

Instead of using ext4_bread/ext4_getblk.

When I was trying out Linux 5.19-rc3 some symlinks became inaccessible to
me, with the error "Structure needs cleaning" and the following printed in
the kernel message log:

EXT4-fs error (device nvme0n1p1): ext4_map_blocks:599: inode #7351350:
block 774843950: comm readlink: lblock 0 mapped to illegal pblock
774843950 (length 1)

It looks like the ext4_get_link function introduced in commit 6493792d3299
("ext4: convert symlink external data block mapping to bdev") does not
handle links with inline data correctly. I added explicit handling for this
case using ext4_readpage_inline. This fixes the bug and the affected
symlinks become accessible again.

Fixes: 6493792d3299 ("ext4: convert symlink external data block mapping to bdev")
Signed-off-by: Torge Matthies <openglfreak@...glemail.com>
---
 fs/ext4/symlink.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
index d281f5bcc526..ec4fc2d23efc 100644
--- a/fs/ext4/symlink.c
+++ b/fs/ext4/symlink.c
@@ -19,7 +19,10 @@
  */
 
 #include <linux/fs.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
 #include <linux/namei.h>
+#include <linux/pagemap.h>
 #include "ext4.h"
 #include "xattr.h"
 
@@ -65,6 +68,37 @@ static int ext4_encrypted_symlink_getattr(struct user_namespace *mnt_userns,
 	return fscrypt_symlink_getattr(path, stat);
 }
 
+static void ext4_free_link_inline(void *folio)
+{
+	folio_unlock(folio);
+	folio_put(folio);
+}
+
+static const char *ext4_get_link_inline(struct inode *inode,
+					struct delayed_call *callback)
+{
+	struct folio *folio;
+	char *ret;
+	int err;
+
+	folio = folio_alloc(GFP_NOFS, 0);
+	if (!folio)
+		return ERR_PTR(-ENOMEM);
+	folio_lock(folio);
+	folio->index = 0;
+
+	err = ext4_readpage_inline(inode, &folio->page);
+	if (err) {
+		folio_put(folio);
+		return ERR_PTR(err);
+	}
+
+	set_delayed_call(callback, ext4_free_link_inline, folio);
+	ret = folio_address(folio);
+	nd_terminate_link(ret, inode->i_size, inode->i_sb->s_blocksize - 1);
+	return ret;
+}
+
 static void ext4_free_link(void *bh)
 {
 	brelse(bh);
@@ -75,6 +109,9 @@ static const char *ext4_get_link(struct dentry *dentry, struct inode *inode,
 {
 	struct buffer_head *bh;
 
+	if (ext4_has_inline_data(inode))
+		return ext4_get_link_inline(inode, callback);
+
 	if (!dentry) {
 		bh = ext4_getblk(NULL, inode, 0, EXT4_GET_BLOCKS_CACHED_NOWAIT);
 		if (IS_ERR(bh))
-- 
2.36.1