[syzbot] [overlayfs?] general protection fault in clone_private_mount

[syzbot] [overlayfs?] general protection fault in clone_private_mount

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    808eb958781e Add linux-next specific files for 20250206
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=126e33df980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=88b25e5d30d576e4
dashboard link: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
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=16346df8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117e80e4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/493ef93f2e5f/disk-808eb958.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b41757cd41c9/vmlinux-808eb958.xz
kernel image: https://storage.googleapis.com/syzbot-assets/24f456104aad/bzImage-808eb958.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
CPU: 0 UID: 0 PID: 5834 Comm: syz-executor772 Not tainted 6.14.0-rc1-next-20250206-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425
Code: 89 d8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 83 c3 48 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 4d 89 fc 74 08 48 89 df e8 db dd e4 ff 48 8b 1b 31 ff
RSP: 0018:ffffc90003e2f958 EFLAGS: 00010206
RAX: 0000000000000009 RBX: 0000000000000048 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888032eb2710
RBP: 0000000000000000 R08: ffffffff8ea81ca7 R09: 1ffffffff1d50394
R10: dffffc0000000000 R11: fffffbfff1d50395 R12: ffff888032eb2700
R13: ffff888032eb2720 R14: 1ffff11006b34091 R15: ffff8880359a0488
FS:  0000555584629380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 00000000786c2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ovl_get_layers fs/overlayfs/super.c:1061 [inline]
 ovl_get_lowerstack fs/overlayfs/super.c:1156 [inline]
 ovl_fill_super+0x1a24/0x3560 fs/overlayfs/super.c:1404
 vfs_get_super fs/super.c:1280 [inline]
 get_tree_nodev+0xb7/0x140 fs/super.c:1299
 vfs_get_tree+0x90/0x2b0 fs/super.c:1814
 do_new_mount+0x2be/0xb40 fs/namespace.c:3659
 do_mount fs/namespace.c:3999 [inline]
 __do_sys_mount fs/namespace.c:4210 [inline]
 __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4187
 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: 0033:0x7f9d7cd98329
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 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:00007ffdbd4bd438 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00007f9d7cd98329
RDX: 0000200000000180 RSI: 0000200000000140 RDI: 0000000000000000
RBP: 00007f9d7ce0b610 R08: 00002000000001c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffdbd4bd608 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425
Code: 89 d8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 83 c3 48 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 4d 89 fc 74 08 48 89 df e8 db dd e4 ff 48 8b 1b 31 ff
RSP: 0018:ffffc90003e2f958 EFLAGS: 00010206
RAX: 0000000000000009 RBX: 0000000000000048 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888032eb2710
RBP: 0000000000000000 R08: ffffffff8ea81ca7 R09: 1ffffffff1d50394
R10: dffffc0000000000 R11: fffffbfff1d50395 R12: ffff888032eb2700
R13: ffff888032eb2720 R14: 1ffff11006b34091 R15: ffff8880359a0488
FS:  0000555584629380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000066c7e0 CR3: 00000000786c2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	89 d8                	mov    %ebx,%eax
   2:	48 83 c4 10          	add    $0x10,%rsp
   6:	5b                   	pop    %rbx
   7:	41 5c                	pop    %r12
   9:	41 5d                	pop    %r13
   b:	41 5e                	pop    %r14
   d:	41 5f                	pop    %r15
   f:	5d                   	pop    %rbp
  10:	c3                   	ret
  11:	cc                   	int3
  12:	cc                   	int3
  13:	cc                   	int3
  14:	cc                   	int3
  15:	48 83 c3 48          	add    $0x48,%rbx
  19:	48 89 d8             	mov    %rbx,%rax
  1c:	48 c1 e8 03          	shr    $0x3,%rax
  20:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  27:	fc ff df
* 2a:	80 3c 08 00          	cmpb   $0x0,(%rax,%rcx,1) <-- trapping instruction
  2e:	4d 89 fc             	mov    %r15,%r12
  31:	74 08                	je     0x3b
  33:	48 89 df             	mov    %rbx,%rdi
  36:	e8 db dd e4 ff       	call   0xffe4de16
  3b:	48 8b 1b             	mov    (%rbx),%rbx
  3e:	31 ff                	xor    %edi,%edi


---
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.

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] [overlayfs?] general protection fault in clone_private_mount

[Amir Goldstein]

On Thu, Feb 6, 2025 at 2:32 PM syzbot
<syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    808eb958781e Add linux-next specific files for 20250206
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=126e33df980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=88b25e5d30d576e4
> dashboard link: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
> 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=16346df8580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117e80e4580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/493ef93f2e5f/disk-808eb958.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b41757cd41c9/vmlinux-808eb958.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/24f456104aad/bzImage-808eb958.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
> CPU: 0 UID: 0 PID: 5834 Comm: syz-executor772 Not tainted 6.14.0-rc1-next-20250206-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
> RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425

Christian,

This obviously points to line:

      /* Make sure this isn't something purely kernel internal. */
     if (!is_anon_ns(old_mnt->mnt_ns))

in commit:
ae63304102ecd fs: allow detached mounts in clone_private_mount()

Where old_mnt->mnt_ns can be NULL.

Thanks,
Amir.

[PATCH] fs: prevent access to ns if it is not mounted

[Lizhi Xu]

syzbot reported a null ptr deref in clone_private_mount. [1]

The mnt_ns member should be accessed after confirming that it has been mounted.

[1]
KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
CPU: 0 UID: 0 PID: 5834 Comm: syz-executor772 Not tainted 6.14.0-rc1-next-20250206-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425
Code: 89 d8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc 48 83 c3 48 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 4d 89 fc 74 08 48 89 df e8 db dd e4 ff 48 8b 1b 31 ff
RSP: 0018:ffffc90003e2f958 EFLAGS: 00010206
RAX: 0000000000000009 RBX: 0000000000000048 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888032eb2710
RBP: 0000000000000000 R08: ffffffff8ea81ca7 R09: 1ffffffff1d50394
R10: dffffc0000000000 R11: fffffbfff1d50395 R12: ffff888032eb2700
R13: ffff888032eb2720 R14: 1ffff11006b34091 R15: ffff8880359a0488
FS:  0000555584629380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 00000000786c2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ovl_get_layers fs/overlayfs/super.c:1061 [inline]
 ovl_get_lowerstack fs/overlayfs/super.c:1156 [inline]
 ovl_fill_super+0x1a24/0x3560 fs/overlayfs/super.c:1404
 vfs_get_super fs/super.c:1280 [inline]
 get_tree_nodev+0xb7/0x140 fs/super.c:1299
 vfs_get_tree+0x90/0x2b0 fs/super.c:1814
 do_new_mount+0x2be/0xb40 fs/namespace.c:3659
 do_mount fs/namespace.c:3999 [inline]
 __do_sys_mount fs/namespace.c:4210 [inline]
 __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4187
 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-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
---
 fs/namespace.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 1314f11ed961..8e2ff3dbab58 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2421,6 +2421,9 @@ struct vfsmount *clone_private_mount(const struct path *path)
 		if (!check_mnt(old_mnt))
 			return ERR_PTR(-EINVAL);
 	} else {
+		if (!is_mounted(&old_mnt->mnt))
+			return ERR_PTR(-EINVAL);
+
 		/* Make sure this isn't something purely kernel internal. */
 		if (!is_anon_ns(old_mnt->mnt_ns))
 			return ERR_PTR(-EINVAL);
-- 
2.43.0

Re: [PATCH] fs: prevent access to ns if it is not mounted

[Amir Goldstein]

On Fri, Feb 7, 2025 at 8:13 AM Lizhi Xu <lizhi.xu@windriver.com> wrote:
>
> syzbot reported a null ptr deref in clone_private_mount. [1]
>
> The mnt_ns member should be accessed after confirming that it has been mounted.
>
> [1]
> KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
> CPU: 0 UID: 0 PID: 5834 Comm: syz-executor772 Not tainted 6.14.0-rc1-next-20250206-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
> RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425

The splat beyond this point is mainly noise I think and referencing [1] is also
a bit weird in the context of this short message

> Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com

Missing:
Fixes: ae63304102ecd ("fs: allow detached mounts in clone_private_mount()")

> Closes: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> ---
>  fs/namespace.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 1314f11ed961..8e2ff3dbab58 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2421,6 +2421,9 @@ struct vfsmount *clone_private_mount(const struct path *path)
>                 if (!check_mnt(old_mnt))
>                         return ERR_PTR(-EINVAL);
>         } else {
> +               if (!is_mounted(&old_mnt->mnt))
> +                       return ERR_PTR(-EINVAL);
> +
>                 /* Make sure this isn't something purely kernel internal. */
>                 if (!is_anon_ns(old_mnt->mnt_ns))
>                         return ERR_PTR(-EINVAL);

Do we still need the second check if we have the first one?

Thanks,
Amir.

Re: [PATCH] fs: prevent access to ns if it is not mounted

[Christian Brauner]

On Fri, Feb 07, 2025 at 01:42:50PM +0100, Amir Goldstein wrote:
> On Fri, Feb 7, 2025 at 8:13 AM Lizhi Xu <lizhi.xu@windriver.com> wrote:
> >
> > syzbot reported a null ptr deref in clone_private_mount. [1]
> >
> > The mnt_ns member should be accessed after confirming that it has been mounted.
> >
> > [1]
> > KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
> > CPU: 0 UID: 0 PID: 5834 Comm: syz-executor772 Not tainted 6.14.0-rc1-next-20250206-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> > RIP: 0010:is_anon_ns fs/mount.h:159 [inline]
> > RIP: 0010:clone_private_mount+0x184/0x3e0 fs/namespace.c:2425
> 
> The splat beyond this point is mainly noise I think and referencing [1] is also
> a bit weird in the context of this short message
> 
> > Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com
> 
> Missing:
> Fixes: ae63304102ecd ("fs: allow detached mounts in clone_private_mount()")
> 
> > Closes: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
> > Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> > ---
> >  fs/namespace.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/namespace.c b/fs/namespace.c
> > index 1314f11ed961..8e2ff3dbab58 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -2421,6 +2421,9 @@ struct vfsmount *clone_private_mount(const struct path *path)
> >                 if (!check_mnt(old_mnt))
> >                         return ERR_PTR(-EINVAL);
> >         } else {
> > +               if (!is_mounted(&old_mnt->mnt))
> > +                       return ERR_PTR(-EINVAL);
> > +
> >                 /* Make sure this isn't something purely kernel internal. */
> >                 if (!is_anon_ns(old_mnt->mnt_ns))
> >                         return ERR_PTR(-EINVAL);
> 
> Do we still need the second check if we have the first one?

Yes, is_mounted() checks whether this is NULL or ERR_PTR(-EINVAL) and
is_anon_ns() checks for null mntns->seq.

I'll fold this fix referencing it in the commit message.

Re: [syzbot] [overlayfs?] general protection fault in clone_private_mount

[syzbot]

syzbot has bisected this issue to:

commit ae63304102ecd597130ecea27395739a6a6371b7
Author: Christian Brauner <brauner@kernel.org>
Date:   Thu Jan 23 19:19:48 2025 +0000

    fs: allow detached mounts in clone_private_mount()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10cb5ca4580000
start commit:   808eb958781e Add linux-next specific files for 20250206
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=12cb5ca4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=14cb5ca4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=88b25e5d30d576e4
dashboard link: https://syzkaller.appspot.com/bug?extid=62dfea789a2cedac1298
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16346df8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117e80e4580000

Reported-by: syzbot+62dfea789a2cedac1298@syzkaller.appspotmail.com
Fixes: ae63304102ec ("fs: allow detached mounts in clone_private_mount()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection