linux-ext4 - [PATCH] ext4: fix race writing to an inline_data file while its xattrs are changing

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Message-Id: <20210821035427.1471851-1-tytso@mit.edu>
Date:   Fri, 20 Aug 2021 23:54:27 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     syzkaller-bugs@...glegroups.com, "Theodore Ts'o" <tytso@....edu>,
        stable@...nel.org,
        syzbot+13146364637c7363a7de@...kaller.appspotmail.com
Subject: [PATCH] ext4: fix race writing to an inline_data file while its xattrs are changing

The location of the system.data extended attribute can change whenever
xattr_sem is not taken.  So we need to recalculate the i_inline_off
field since it mgiht have changed between ext4_write_begin() and
ext4_write_end().

This means that caching i_inline_off is probably not helpful, so in
the long run we should probably get rid of it and shrink the in-memory
ext4 inode slightly, but let's fix the race the simple way for now.

Cc: stable@...nel.org
Fixes: f19d5870cbf72 ("ext4: add normal write support for inline data")
Reported-by: syzbot+13146364637c7363a7de@...kaller.appspotmail.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 fs/ext4/inline.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 70cb64db33f7..24e994e75f5c 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -750,6 +750,12 @@ int ext4_write_inline_data_end(struct inode *inode, loff_t pos, unsigned len,
 	ext4_write_lock_xattr(inode, &no_expand);
 	BUG_ON(!ext4_has_inline_data(inode));
 
+	/*
+	 * ei->i_inline_off may have changed since ext4_write_begin()
+	 * called ext4_try_to_write_inline_data()
+	 */
+	(void) ext4_find_inline_data_nolock(inode);
+
 	kaddr = kmap_atomic(page);
 	ext4_write_inline_data(inode, &iloc, kaddr, pos, len);
 	kunmap_atomic(kaddr);
-- 
2.31.0