Re: [syzbot] general protection fault in ovl_dentry_upper

From: Miklos Szeredi
Date: Thu Nov 24 2022 - 07:42:39 EST

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

On Thu, 24 Nov 2022 at 05:51, syzbot
<syzbot+a4055c78774bbf3498bb@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: fe24a97cf254 Merge tag 'input-for-v6.1-rc5' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15a02765880000
> kernel config: https://syzkaller.appspot.com/x/.config?x=6f9416d398342c83
> dashboard link: https://syzkaller.appspot.com/bug?extid=a4055c78774bbf3498bb
> compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10a320fd880000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10e6b6ed880000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/d4424ef25058/disk-fe24a97c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/61c4ed6a96dd/vmlinux-fe24a97c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d1b8ff061e4e/bzImage-fe24a97c.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a4055c78774bbf3498bb@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> general protection fault, probably for non-canonical address 0xdffffc0000000092: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000490-0x0000000000000497]
> CPU: 0 PID: 16299 Comm: syz-executor309 Not tainted 6.1.0-rc5-syzkaller-00307-gfe24a97cf254 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:ovl_upperdentry_dereference fs/overlayfs/ovl_entry.h:150 [inline]
> RIP: 0010:ovl_dentry_upper+0x40/0x60 fs/overlayfs/util.c:213
> Code: fe 49 83 c6 68 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 7f 28 e9 fe bb 90 04 00 00 49 03 1e 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 61 28 e9 fe 48 8b 03 5b 41 5e 41
> RSP: 0018:ffffc9000ef3fa50 EFLAGS: 00010202
> RAX: 0000000000000092 RBX: 0000000000000490 RCX: ffff888020328000
> RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff888075528758
> RBP: dffffc0000000000 R08: ffffffff81f2119e R09: ffffed100eaa50fa
> R10: ffffed100eaa50fa R11: 1ffff1100eaa50f9 R12: 0000000000000040
> R13: ffffc9000ef3fc20 R14: ffff8880755287c0 R15: dffffc0000000000
> FS: 00007f7e44d61700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7e44df1800 CR3: 000000007c404000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> ovl_dentry_revalidate_common fs/overlayfs/super.c:146 [inline]
> ovl_dentry_revalidate+0x4b/0x380 fs/overlayfs/super.c:159
> d_revalidate fs/namei.c:856 [inline]
> lookup_fast+0x26c/0x480 fs/namei.c:1634
> walk_component+0x55/0x410 fs/namei.c:1989
> lookup_last fs/namei.c:2450 [inline]
> path_lookupat+0x17d/0x450 fs/namei.c:2474
> filename_lookup+0x274/0x650 fs/namei.c:2503
> user_path_at_empty+0x40/0x1a0 fs/namei.c:2876
> user_path_at include/linux/namei.h:57 [inline]
> __do_sys_name_to_handle_at fs/fhandle.c:107 [inline]
> __se_sys_name_to_handle_at+0xf8/0x610 fs/fhandle.c:93
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f7e44db0159
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 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:00007f7e44d612f8 EFLAGS: 00000246 ORIG_RAX: 000000000000012f
> RAX: ffffffffffffffda RBX: 0000000000000034 RCX: 00007f7e44db0159
> RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000003
> RBP: 00007f7e44e394a8 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7e44e394a0
> R13: 00007f7e44e394ac R14: 00007f7e44e06074 R15: 0030656c69662f2e
> </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:ovl_upperdentry_dereference fs/overlayfs/ovl_entry.h:150 [inline]
> RIP: 0010:ovl_dentry_upper+0x40/0x60 fs/overlayfs/util.c:213
> Code: fe 49 83 c6 68 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 7f 28 e9 fe bb 90 04 00 00 49 03 1e 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 61 28 e9 fe 48 8b 03 5b 41 5e 41
> RSP: 0018:ffffc9000ef3fa50 EFLAGS: 00010202
> RAX: 0000000000000092 RBX: 0000000000000490 RCX: ffff888020328000
> RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff888075528758
> RBP: dffffc0000000000 R08: ffffffff81f2119e R09: ffffed100eaa50fa
> R10: ffffed100eaa50fa R11: 1ffff1100eaa50f9 R12: 0000000000000040
> R13: ffffc9000ef3fc20 R14: ffff8880755287c0 R15: dffffc0000000000
> FS: 00007f7e44d61700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000564e6292d008 CR3: 000000007c404000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess), 1 bytes skipped:
> 0: 49 83 c6 68 add $0x68,%r14
> 4: 4c 89 f0 mov %r14,%rax
> 7: 48 c1 e8 03 shr $0x3,%rax
> b: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1)
> 10: 74 08 je 0x1a
> 12: 4c 89 f7 mov %r14,%rdi
> 15: e8 7f 28 e9 fe callq 0xfee92899
> 1a: bb 90 04 00 00 mov $0x490,%ebx
> 1f: 49 03 1e add (%r14),%rbx
> 22: 48 89 d8 mov %rbx,%rax
> 25: 48 c1 e8 03 shr $0x3,%rax
> * 29: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) <-- trapping instruction
> 2e: 74 08 je 0x38
> 30: 48 89 df mov %rbx,%rdi
> 33: e8 61 28 e9 fe callq 0xfee92899
> 38: 48 8b 03 mov (%rbx),%rax
> 3b: 5b pop %rbx
> 3c: 41 5e pop %r14
> 3e: 41 rex.B
>
>
> ---
> 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@xxxxxxxxxxxxxxxx.
>
> syzbot will keep track of this issue. See:
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> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
From: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
Subject: ovl: fix use inode directly in rcu-walk mode

ovl_dentry_revalidate_common() can be called in rcu-walk mode. As document
said, "in rcu-walk mode, d_parent and d_inode should not be used without
care".

Check inode here to protect access under rcu-walk mode.

Fixes: bccece1ead36 ("ovl: allow remote upper")
Reported-by: syzbot+a4055c78774bbf3498bb@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.7
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
fs/overlayfs/super.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -139,11 +139,16 @@ static int ovl_dentry_revalidate_common(
unsigned int flags, bool weak)
{
struct ovl_entry *oe = dentry->d_fsdata;
+ struct inode *inode = d_inode_rcu(dentry);
struct dentry *upper;
unsigned int i;
int ret = 1;

- upper = ovl_dentry_upper(dentry);
+ /* Careful in RCU mode */
+ if (!inode)
+ return -ECHILD;
+
+ upper = ovl_i_dentry_upper(inode);
if (upper)
ret = ovl_revalidate_real(upper, flags, weak);