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From:   Dongliang Mu <dzm91@hust.edu.cn>
To:     Gao Xiang <xiang@kernel.org>, Chao Yu <chao@kernel.org>
Cc:     Dongliang Mu <mudongliangabcd@gmail.com>,
        syzkaller <syzkaller@googlegroups.com>,
        linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH] fs: erofs: remember if kobject_init_and_add was done
Date:   Tue, 15 Mar 2022 15:51:52 +0800
Message-Id: <20220315075152.63789-1-dzm91@hust.edu.cn>
MIME-Version: 1.0
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From: Dongliang Mu <mudongliangabcd@gmail.com>

Syzkaller hit 'WARNING: kobject bug in erofs_unregister_sysfs'. This bug
is triggered by injecting fault in kobject_init_and_add of
erofs_unregister_sysfs.

Fix this by remembering if kobject_init_and_add is successful.

Note that I've tested the patch and the crash does not occur any more.

Reported-by: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
---
 fs/erofs/internal.h | 1 +
 fs/erofs/sysfs.c    | 9 ++++++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 5aa2cf2c2f80..9e20665e3f68 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -144,6 +144,7 @@ struct erofs_sb_info {
 	u32 feature_incompat;
 
 	/* sysfs support */
+	bool s_sysfs_inited;
 	struct kobject s_kobj;		/* /sys/fs/erofs/<devname> */
 	struct completion s_kobj_unregister;
 };
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index dac252bc9228..2b48a4df19b4 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -209,6 +209,7 @@ int erofs_register_sysfs(struct super_block *sb)
 				   "%s", sb->s_id);
 	if (err)
 		goto put_sb_kobj;
+	sbi->s_sysfs_inited = true;
 	return 0;
 
 put_sb_kobj:
@@ -221,9 +222,11 @@ void erofs_unregister_sysfs(struct super_block *sb)
 {
 	struct erofs_sb_info *sbi = EROFS_SB(sb);
 
-	kobject_del(&sbi->s_kobj);
-	kobject_put(&sbi->s_kobj);
-	wait_for_completion(&sbi->s_kobj_unregister);
+	if (sbi->s_sysfs_inited) {
+		kobject_del(&sbi->s_kobj);
+		kobject_put(&sbi->s_kobj);
+		wait_for_completion(&sbi->s_kobj_unregister);
+	}
 }
 
 int __init erofs_init_sysfs(void)
-- 
2.25.1