linux-kernel - [PATCH v2] f2fs: fix use-after-free issue

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Date:   Fri, 24 Jul 2020 09:38:11 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>,
        Li Guifu <bluce.liguifu@...wei.com>,
        Chao Yu <yuchao0@...wei.com>
Subject: [PATCH v2] f2fs: fix use-after-free issue

From: Li Guifu <bluce.liguifu@...wei.com>

During umount, f2fs_put_super() unregisters procfs entries after
f2fs_destroy_segment_manager(), it may cause use-after-free
issue when umount races with procfs accessing, fix it by relocating
f2fs_unregister_sysfs().

[Chao Yu: change commit title/message a bit]

Signed-off-by: Li Guifu <bluce.liguifu@...wei.com>
Reviewed-by: Chao Yu <yuchao0@...wei.com>
---
v2:
- fix typo in commit message.
- improve comment in f2fs_put_super() a bit.
 fs/f2fs/super.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 80cb7cd358f8..5e0a3eeb8ca4 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1175,6 +1175,9 @@ static void f2fs_put_super(struct super_block *sb)
 	int i;
 	bool dropped;
 
+	/* unregister procfs/sysfs entries in advance to avoid race case */
+	f2fs_unregister_sysfs(sbi);
+
 	f2fs_quota_off_umount(sb);
 
 	/* prevent remaining shrinker jobs */
@@ -1240,8 +1243,6 @@ static void f2fs_put_super(struct super_block *sb)
 
 	kvfree(sbi->ckpt);
 
-	f2fs_unregister_sysfs(sbi);
-
 	sb->s_fs_info = NULL;
 	if (sbi->s_chksum_driver)
 		crypto_free_shash(sbi->s_chksum_driver);
-- 
2.26.2