linux-kernel - [PATCH V2] nilfs2: prevent use of deleted inode

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Message-ID: <tencent_B7D4EAEAED76CDAC79026EF02F4D6D5C950A@qq.com>
Date: Sun,  8 Dec 2024 11:24:14 +0800
From: Edward Adam Davis <eadavis@...com>
To: konishi.ryusuke@...il.com
Cc: eadavis@...com,
	linux-kernel@...r.kernel.org,
	linux-nilfs@...r.kernel.org,
	syzbot+9260555647a5132edd48@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH V2] nilfs2: prevent use of deleted inode

syzbot reported a WARNING in nilfs_rmdir. [1]

Because the inode bitmap is corrupted, an inode with an inode number
that should exist as a ".nilfs" file was reassigned by nilfs_mkdir for
"file0", causing an inode duplication during execution.
And this causes an underflow of i_nlink in rmdir operations.

Avoid to this issue, check i_nlink in nilfs_iget(), if it is 0, it means
that this inode has been deleted, and iput is executed to reclaim it.

[1]
WARNING: CPU: 1 PID: 5824 at fs/inode.c:407 drop_nlink+0xc4/0x110 fs/inode.c:407
Modules linked in:
CPU: 1 UID: 0 PID: 5824 Comm: syz-executor223 Not tainted 6.12.0-syzkaller-12113-gbcc8eda6d349 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:drop_nlink+0xc4/0x110 fs/inode.c:407
Code: bb 70 07 00 00 be 08 00 00 00 e8 57 0b e6 ff f0 48 ff 83 70 07 00 00 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc e8 9d 4c 7e ff 90 <0f> 0b 90 eb 83 44 89 e1 80 e1 07 80 c1 03 38 c1 0f 8c 5c ff ff ff
RSP: 0018:ffffc900037f7c70 EFLAGS: 00010293
RAX: ffffffff822124a3 RBX: 1ffff1100e7ae034 RCX: ffff88807cf53c00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff82212423 R09: 1ffff1100f8ba8ee
R10: dffffc0000000000 R11: ffffed100f8ba8ef R12: ffff888073d701a0
R13: 1ffff1100e79f5c4 R14: ffff888073d70158 R15: dffffc0000000000
FS:  0000555558d1e480(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555558d37878 CR3: 000000007d920000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 nilfs_rmdir+0x1b0/0x250 fs/nilfs2/namei.c:342
 vfs_rmdir+0x3a3/0x510 fs/namei.c:4394
 do_rmdir+0x3b5/0x580 fs/namei.c:4453
 __do_sys_rmdir fs/namei.c:4472 [inline]
 __se_sys_rmdir fs/namei.c:4470 [inline]
 __x64_sys_rmdir+0x47/0x50 fs/namei.c:4470
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported-and-tested-by: syzbot+9260555647a5132edd48@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9260555647a5132edd48
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
V1 -> V2: Adjust the patch as suggested by Ryusuke Konishi

 fs/nilfs2/inode.c | 8 +++++++-
 fs/nilfs2/namei.c | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index cf9ba481ae37..b7d4105f37bf 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -544,8 +544,14 @@ struct inode *nilfs_iget(struct super_block *sb, struct nilfs_root *root,
 	inode = nilfs_iget_locked(sb, root, ino);
 	if (unlikely(!inode))
 		return ERR_PTR(-ENOMEM);
-	if (!(inode->i_state & I_NEW))
+
+	if (!(inode->i_state & I_NEW)) {
+		if (!inode->i_nlink) {
+			iput(inode);
+			return ERR_PTR(-ESTALE);
+		}
 		return inode;
+	}
 
 	err = __nilfs_read_inode(sb, root, ino, inode);
 	if (unlikely(err)) {
diff --git a/fs/nilfs2/namei.c b/fs/nilfs2/namei.c
index 9b108052d9f7..7037f47c454f 100644
--- a/fs/nilfs2/namei.c
+++ b/fs/nilfs2/namei.c
@@ -67,6 +67,12 @@ nilfs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 		inode = NULL;
 	} else {
 		inode = nilfs_iget(dir->i_sb, NILFS_I(dir)->i_root, ino);
+		if (inode == ERR_PTR(-ESTALE)) {
+			nilfs_error(dir->i_sb, __func__,
+					"deleted inode referenced: %lu",
+					(unsigned long) ino);
+			return ERR_PTR(-EIO);
+		}
 	}
 
 	return d_splice_alias(inode, dentry);
-- 
2.47.0