linux-ext4 - [PATCH 1/1] fs/ext2: Avoid page_address on pages returned by ext2_get

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Message-Id: <20210713165918.10da0318af5b9b73e599a517@urjc.es>
Date:   Tue, 13 Jul 2021 16:59:18 +0200
From:   Javier Pello <javier.pello@...c.es>
To:     Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] fs/ext2: Avoid page_address on pages returned by
 ext2_get_page

From: Javier Pello <javier.pello@...c.es>

Commit 782b76d7abdf02b12c46ed6f1e9bf715569027f7 ("fs/ext2: Replace
kmap() with kmap_local_page()") replaced the kmap/kunmap calls in
ext2_get_page/ext2_put_page with kmap_local_page/kunmap_local for
efficiency reasons. As a necessary side change, the commit also
made ext2_get_page (and ext2_find_entry and ext2_dotdot) return
the mapping address along with the page itself, as it is required
for kunmap_local, and converted uses of page_address on such pages
to use the newly returned address instead. However, uses of
page_address on such pages were missed in ext2_check_page and
ext2_delete_entry, which triggers oopses if kmap_local_page happens
to return an address from high memory. Fix this now by converting
the remaining uses of page_address to use the right address, as
returned by kmap_local_page.

Signed-off-by: Javier Pello <javier.pello@...c.es>
Fixes: 782b76d7abdf fs/ext2: Replace kmap() with kmap_local_page()
---
 fs/ext2/dir.c   | 20 ++++++++++----------
 fs/ext2/ext2.h  |  3 ++-
 fs/ext2/namei.c |  4 ++--
 3 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
index 14292dba..0c59b4d3 100644
--- a/fs/ext2/dir.c
+++ b/fs/ext2/dir.c
@@ -106,12 +106,11 @@ static int ext2_commit_chunk(struct page *page, loff_t pos, unsigned len)
 	return err;
 }
 
-static bool ext2_check_page(struct page *page, int quiet)
+static bool ext2_check_page(struct page *page, int quiet, char *kaddr)
 {
 	struct inode *dir = page->mapping->host;
 	struct super_block *sb = dir->i_sb;
 	unsigned chunk_size = ext2_chunk_size(dir);
-	char *kaddr = page_address(page);
 	u32 max_inumber = le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count);
 	unsigned offs, rec_len;
 	unsigned limit = PAGE_SIZE;
@@ -205,7 +204,8 @@ static struct page * ext2_get_page(struct inode *dir, unsigned long n,
 	if (!IS_ERR(page)) {
 		*page_addr = kmap_local_page(page);
 		if (unlikely(!PageChecked(page))) {
-			if (PageError(page) || !ext2_check_page(page, quiet))
+			if (PageError(page) || !ext2_check_page(page, quiet,
+								*page_addr))
 				goto fail;
 		}
 	}
@@ -584,16 +584,16 @@ int ext2_add_link (struct dentry *dentry, struct inode *inode)
  * ext2_delete_entry deletes a directory entry by merging it with the
  * previous entry. Page is up-to-date.
  */
-int ext2_delete_entry (struct ext2_dir_entry_2 * dir, struct page * page )
+int ext2_delete_entry (struct ext2_dir_entry_2 *dir, struct page *page,
+			void *kaddr)
 {
 	struct inode *inode = page->mapping->host;
-	char *kaddr = page_address(page);
-	unsigned from = ((char*)dir - kaddr) & ~(ext2_chunk_size(inode)-1);
-	unsigned to = ((char *)dir - kaddr) +
-				ext2_rec_len_from_disk(dir->rec_len);
+	unsigned int delta = (char *)dir - (char *)kaddr;
+	unsigned int from = delta & ~(ext2_chunk_size(inode)-1);
+	unsigned int to = delta + ext2_rec_len_from_disk(dir->rec_len);
 	loff_t pos;
 	ext2_dirent * pde = NULL;
-	ext2_dirent * de = (ext2_dirent *) (kaddr + from);
+	ext2_dirent *de = (ext2_dirent *) ((char *)kaddr + from);
 	int err;
 
 	while ((char*)de < (char*)dir) {
@@ -607,7 +607,7 @@ int ext2_delete_entry (struct ext2_dir_entry_2 * dir, struct page * page )
 		de = ext2_next_entry(de);
 	}
 	if (pde)
-		from = (char*)pde - (char*)page_address(page);
+		from = (char *)pde - (char *)kaddr;
 	pos = page_offset(page) + from;
 	lock_page(page);
 	err = ext2_prepare_chunk(page, pos, to - from);
diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
index b0a69482..7bda9379 100644
--- a/fs/ext2/ext2.h
+++ b/fs/ext2/ext2.h
@@ -740,7 +740,8 @@ extern int ext2_inode_by_name(struct inode *dir,
 extern int ext2_make_empty(struct inode *, struct inode *);
 extern struct ext2_dir_entry_2 *ext2_find_entry(struct inode *, const struct qstr *,
 						struct page **, void **res_page_addr);
-extern int ext2_delete_entry (struct ext2_dir_entry_2 *, struct page *);
+extern int ext2_delete_entry(struct ext2_dir_entry_2 *dir, struct page *page,
+			     void *kaddr);
 extern int ext2_empty_dir (struct inode *);
 extern struct ext2_dir_entry_2 *ext2_dotdot(struct inode *dir, struct page **p, void **pa);
 extern void ext2_set_link(struct inode *, struct ext2_dir_entry_2 *, struct page *, void *,
diff --git a/fs/ext2/namei.c b/fs/ext2/namei.c
index 1f69b816..5f6b7560 100644
--- a/fs/ext2/namei.c
+++ b/fs/ext2/namei.c
@@ -293,7 +293,7 @@ static int ext2_unlink(struct inode * dir, struct dentry *dentry)
 		goto out;
 	}
 
-	err = ext2_delete_entry (de, page);
+	err = ext2_delete_entry (de, page, page_addr);
 	ext2_put_page(page, page_addr);
 	if (err)
 		goto out;
@@ -397,7 +397,7 @@ static int ext2_rename (struct user_namespace * mnt_userns,
 	old_inode->i_ctime = current_time(old_inode);
 	mark_inode_dirty(old_inode);
 
-	ext2_delete_entry(old_de, old_page);
+	ext2_delete_entry(old_de, old_page, old_page_addr);
 
 	if (dir_de) {
 		if (old_dir != new_dir)
-- 
2.30.1