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From: "Theodore Ts'o" <tytso@mit.edu>
To: Ext4 Developers List <linux-ext4@vger.kernel.org>
Cc: syzkaller-bugs@googlegroups.com, "Theodore Ts'o" <tytso@mit.edu>,
	stable@kernel.org,
	syzbot+13146364637c7363a7de@syzkaller.appspotmail.com
Subject: [PATCH] ext4: fix race writing to an inline_data file while its xattrs are changing
Date: Fri, 20 Aug 2021 23:54:27 -0400	[thread overview]
Message-ID: <20210821035427.1471851-1-tytso@mit.edu> (raw)
In-Reply-To: <000000000000e5080305c9e51453@google.com>

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@kernel.org
Fixes: f19d5870cbf72 ("ext4: add normal write support for inline data")
Reported-by: syzbot+13146364637c7363a7de@syzkaller.appspotmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.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


  parent reply	other threads:[~2021-08-21  3:55 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-19  8:10 [syzbot] KASAN: slab-out-of-bounds Write in ext4_write_inline_data_end syzbot
2021-08-21  3:43 ` Theodore Ts'o
2021-08-21  3:54 ` Theodore Ts'o [this message]
2021-08-21  4:07   ` [PATCH] ext4: fix race writing to an inline_data file while its xattrs are changing Theodore Ts'o
2021-08-21  4:53     ` [syzbot] KASAN: slab-out-of-bounds Write in ext4_write_inline_data_end syzbot

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