From 9b5a04ac3ad9898c4745cba46ea26de74ba56a8e Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Date: Wed, 10 May 2023 00:29:56 +0900
Subject: [PATCH] nilfs2: fix use-after-free bug of nilfs_root in nilfs_evict_inode()
Git-commit: 9b5a04ac3ad9898c4745cba46ea26de74ba56a8e
Patch-mainline: v6.4-rc3
References: git-fixes
During unmount process of nilfs2, nothing holds nilfs_root structure after
nilfs2 detaches its writer in nilfs_detach_log_writer(). However, since
nilfs_evict_inode() uses nilfs_root for some cleanup operations, it may
cause use-after-free read if inodes are left in "garbage_list" and
released by nilfs_dispose_list() at the end of nilfs_detach_log_writer().
Fix this issue by modifying nilfs_evict_inode() to only clear inode
without additional metadata changes that use nilfs_root if the file system
is degraded to read-only or the writer is detached.
Link: https://lkml.kernel.org/r/20230509152956.8313-1-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+78d4495558999f55d1da@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/00000000000099e5ac05fb1c3b85@google.com
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
fs/nilfs2/inode.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 1310d2d5feb3..a8ce522ac747 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -917,6 +917,7 @@ void nilfs_evict_inode(struct inode *inode)
struct nilfs_transaction_info ti;
struct super_block *sb = inode->i_sb;
struct nilfs_inode_info *ii = NILFS_I(inode);
+ struct the_nilfs *nilfs;
int ret;
if (inode->i_nlink || !ii->i_root || unlikely(is_bad_inode(inode))) {
@@ -929,6 +930,23 @@ void nilfs_evict_inode(struct inode *inode)
truncate_inode_pages_final(&inode->i_data);
+ nilfs = sb->s_fs_info;
+ if (unlikely(sb_rdonly(sb) || !nilfs->ns_writer)) {
+ /*
+ * If this inode is about to be disposed after the file system
+ * has been degraded to read-only due to file system corruption
+ * or after the writer has been detached, do not make any
+ * changes that cause writes, just clear it.
+ * Do this check after read-locking ns_segctor_sem by
+ * nilfs_transaction_begin() in order to avoid a race with
+ * the writer detach operation.
+ */
+ clear_inode(inode);
+ nilfs_clear_inode(inode);
+ nilfs_transaction_abort(sb);
+ return;
+ }
+
/* TODO: some of the following operations may fail. */
nilfs_truncate_bmap(ii, 0);
nilfs_mark_inode_dirty(inode);
--
2.35.3