[syzbot] [hfs?] WARNING in hfsplus_unlink

[syzbot] [hfs?] WARNING in hfsplus_unlink

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bf9aa14fc523 Merge tag 'timers-core-2024-11-18' of git://g..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=154e4b78580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ccd6152c3e2378ce
dashboard link: https://syzkaller.appspot.com/bug?extid=028180f480a74961919c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1676475f980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ff46c0580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f7f38a2c24fc/disk-bf9aa14f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9fe13f1c9a0f/vmlinux-bf9aa14f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/04d354ff9f6b/bzImage-bf9aa14f.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/64b16595572b/mount_0.gz

Bisection is inconclusive: the issue happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=148be930580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=168be930580000
console output: https://syzkaller.appspot.com/x/log.txt?x=128be930580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+028180f480a74961919c@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 1024
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5831 at fs/inode.c:407 drop_nlink+0xc4/0x110 fs/inode.c:407
Modules linked in:
CPU: 1 UID: 0 PID: 5831 Comm: syz-executor234 Not tainted 6.12.0-syzkaller-01782-gbf9aa14fc523 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
RIP: 0010:drop_nlink+0xc4/0x110 fs/inode.c:407
Code: bb 70 07 00 00 be 08 00 00 00 e8 07 df e5 ff f0 48 ff 83 70 07 00 00 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc e8 6d f4 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:ffffc9000369fbb0 EFLAGS: 00010293
RAX: ffffffff8215f523 RBX: 1ffff11004ad054f RCX: ffff88802a931e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff8215f4a3 R09: 1ffff920006d3ed8
R10: dffffc0000000000 R11: fffff520006d3ed9 R12: ffff888025682a78
R13: ffff888079eef370 R14: ffff888025682a30 R15: dffffc0000000000
FS:  0000555588597380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000066c7e0 CR3: 0000000078e92000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 hfsplus_unlink+0x3fe/0x790 fs/hfsplus/dir.c:381
 vfs_unlink+0x365/0x650 fs/namei.c:4523
 do_unlinkat+0x4ae/0x830 fs/namei.c:4587
 __do_sys_unlink fs/namei.c:4635 [inline]
 __se_sys_unlink fs/namei.c:4633 [inline]
 __x64_sys_unlink+0x47/0x50 fs/namei.c:4633
 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
RIP: 0033:0x7f81f72e79b9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffbff4f578 EFLAGS: 00000246 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0031656c69662f2e RCX: 00007f81f72e79b9
RDX: ffffffffffffffb8 RSI: 00007f81f72e79b9 RDI: 00000000200000c0
RBP: 00007f81f735b610 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fffbff4f748 R14: 0000000000000001 R15: 0000000000000001
 </TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [hfs?] WARNING in hfsplus_unlink

[Edward Adam Davis]

After the rename syscall fails, the unlink syscall triggers a warning in
drop_nlink() because the i_nlink value is 0.

When unlink succeeds but rename_cat fails in rename, the i_nlink and flags
values of the inode of the new dentry should be restored.

#syz test

diff --git a/fs/hfsplus/dir.c b/fs/hfsplus/dir.c
index f5c4b3e31a1c..b489d22409e7 100644
--- a/fs/hfsplus/dir.c
+++ b/fs/hfsplus/dir.c
@@ -534,7 +534,7 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 			  struct inode *new_dir, struct dentry *new_dentry,
 			  unsigned int flags)
 {
-	int res;
+	int res, unlinked_new = 0;
 
 	if (flags & ~RENAME_NOREPLACE)
 		return -EINVAL;
@@ -543,8 +543,10 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 	if (d_really_is_positive(new_dentry)) {
 		if (d_is_dir(new_dentry))
 			res = hfsplus_rmdir(new_dir, new_dentry);
-		else
+		else {
 			res = hfsplus_unlink(new_dir, new_dentry);
+			unlinked_new = res == 0 && d_inode(new_dentry)->i_flags & S_DEAD;
+		}
 		if (res)
 			return res;
 	}
@@ -554,6 +556,12 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 				 new_dir, &new_dentry->d_name);
 	if (!res)
 		new_dentry->d_fsdata = old_dentry->d_fsdata;
+	else if (unlinked_new) {
+		struct inode *inode = d_inode(new_dentry);
+		set_nlink(inode, inode->i_nlink + 1);
+		inode->i_flags &= ~S_DEAD;
+	}
+
 	return res;
 }
 

Re: [syzbot] [hfs?] WARNING in hfsplus_unlink

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+028180f480a74961919c@syzkaller.appspotmail.com
Tested-by: syzbot+028180f480a74961919c@syzkaller.appspotmail.com

Tested on:

commit:         9f16d5e6 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=162c375f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e92fc420ca55fe33
dashboard link: https://syzkaller.appspot.com/bug?extid=028180f480a74961919c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=177319c0580000

Note: testing is done by a robot and is best-effort only.

[PATCH] hfsplus: restore i_nlink and flags when rename_cat fails

[Edward Adam Davis]

After the rename syscall fails, the unlink syscall triggers a warning in
drop_nlink() because the i_nlink value is 0.

When unlink succeeds but rename_cat fails in rename, the i_nlink and flags
values of the inode of the new dentry should be restored.

Reported-and-tested-by: syzbot+028180f480a74961919c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=028180f480a74961919c
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/hfsplus/dir.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/hfsplus/dir.c b/fs/hfsplus/dir.c
index f5c4b3e31a1c..b489d22409e7 100644
--- a/fs/hfsplus/dir.c
+++ b/fs/hfsplus/dir.c
@@ -534,7 +534,7 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 			  struct inode *new_dir, struct dentry *new_dentry,
 			  unsigned int flags)
 {
-	int res;
+	int res, unlinked_new = 0;
 
 	if (flags & ~RENAME_NOREPLACE)
 		return -EINVAL;
@@ -543,8 +543,10 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 	if (d_really_is_positive(new_dentry)) {
 		if (d_is_dir(new_dentry))
 			res = hfsplus_rmdir(new_dir, new_dentry);
-		else
+		else {
 			res = hfsplus_unlink(new_dir, new_dentry);
+			unlinked_new = res == 0 && d_inode(new_dentry)->i_flags & S_DEAD;
+		}
 		if (res)
 			return res;
 	}
@@ -554,6 +556,12 @@ static int hfsplus_rename(struct mnt_idmap *idmap,
 				 new_dir, &new_dentry->d_name);
 	if (!res)
 		new_dentry->d_fsdata = old_dentry->d_fsdata;
+	else if (unlinked_new) {
+		struct inode *inode = d_inode(new_dentry);
+		set_nlink(inode, inode->i_nlink + 1);
+		inode->i_flags &= ~S_DEAD;
+	}
+
 	return res;
 }
 
-- 
2.43.0