[syzbot] [fs?] general protection fault in grab_requested_root

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc855b77719f Merge tag 'irq-drivers-2026-02-09' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13136ae6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=86c6013ce1247095
dashboard link: https://syzkaller.appspot.com/bug?extid=9e03a9535ea65f687a44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15da0b3a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14e28e5a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a31372ead89f/disk-dc855b77.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/657357081566/vmlinux-dc855b77.xz
kernel image: https://storage.googleapis.com/syzbot-assets/278d7f265ba3/bzImage-dc855b77.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e03a9...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc000000001e: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000000f0-0x00000000000000f7]
CPU: 0 UID: 0 PID: 5998 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:mnt_ns_empty fs/mount.h:197 [inline]
RIP: 0010:grab_requested_root+0xde/0x3c0 fs/namespace.c:5636
Code: 02 00 00 49 39 5d 18 0f 84 cd 01 00 00 e8 0a 10 78 ff 48 8d bb 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 82 02 00 00 48 8b 83 08 01 00 00 48 85 c0 0f 84
RSP: 0018:ffffc90003027d88 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffffffffffea RCX: ffffffff828e8167
RDX: 000000000000001e RSI: ffffffff828e7fb6 RDI: 00000000000000f2
RBP: ffffc90003027db0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802b220000
R13: ffff88803156d4e0 R14: ffff88807b4d7028 R15: ffff88807b4d7010
FS: 000055555e0dd500(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002c608000 CR4: 00000000003526f0
Call Trace:
<TASK>
do_statmount fs/namespace.c:5699 [inline]
__do_sys_statmount+0x359/0x2440 fs/namespace.c:5949
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f12d359bf79
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd0e2fee68 EFLAGS: 00000246 ORIG_RAX: 00000000000001c9
RAX: ffffffffffffffda RBX: 00007f12d3815fa0 RCX: 00007f12d359bf79
RDX: 00000000000001fe RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f12d36327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f12d3815fac R14: 00007f12d3815fa0 R15: 00007f12d3815fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:mnt_ns_empty fs/mount.h:197 [inline]
RIP: 0010:grab_requested_root+0xde/0x3c0 fs/namespace.c:5636
Code: 02 00 00 49 39 5d 18 0f 84 cd 01 00 00 e8 0a 10 78 ff 48 8d bb 08 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 82 02 00 00 48 8b 83 08 01 00 00 48 85 c0 0f 84
RSP: 0018:ffffc90003027d88 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffffffffffea RCX: ffffffff828e8167
RDX: 000000000000001e RSI: ffffffff828e7fb6 RDI: 00000000000000f2
RBP: ffffc90003027db0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802b220000
R13: ffff88803156d4e0 R14: ffff88807b4d7028 R15: ffff88807b4d7010
FS: 000055555e0dd500(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002c608000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 02 00 add (%rax),%al
2: 00 49 39 add %cl,0x39(%rcx)
5: 5d pop %rbp
6: 18 0f sbb %cl,(%rdi)
8: 84 cd test %cl,%ch
a: 01 00 add %eax,(%rax)
c: 00 e8 add %ch,%al
e: 0a 10 or (%rax),%dl
10: 78 ff js 0x11
12: 48 8d bb 08 01 00 00 lea 0x108(%rbx),%rdi
19: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
20: fc ff df
23: 48 89 fa mov %rdi,%rdx
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2e: 0f 85 82 02 00 00 jne 0x2b6
34: 48 8b 83 08 01 00 00 mov 0x108(%rbx),%rax
3b: 48 85 c0 test %rax,%rax
3e: 0f .byte 0xf
3f: 84 .byte 0x84


---
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 syzk...@googlegroups.com.

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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.

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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

[Qing Wang]

#syz test

diff --git a/fs/namespace.c b/fs/namespace.c
index a67cbe42746d..8124f33d89a2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5678,13 +5678,17 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,

s->mnt = mnt_file->f_path.mnt;
ns = real_mount(s->mnt)->mnt_ns;
- if (!ns)
+ if (IS_ERR_OR_NULL(ns)) {
/*
* We can't set mount point and mnt_ns_id since we don't have a
* ns for the mount. This can happen if the mount is unmounted
* with MNT_DETACH.
*/
s->mask &= ~(STATMOUNT_MNT_POINT | STATMOUNT_MNT_NS_ID);
+ if (IS_ERR(ns))
+ return PTR_ERR(ns);
+ ns = NULL;
+ }
} else {
/* Has the namespace already been emptied? */
if (mnt_ns_id && mnt_ns_empty(ns))

[syzbot]

Hello,

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

Reported-by: syzbot+9e03a9...@syzkaller.appspotmail.com
Tested-by: syzbot+9e03a9...@syzkaller.appspotmail.com

Tested on:

commit: cee73b1e Merge tag 'riscv-for-linus-7.0-mw1' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=155f7a52580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fe62ec9519bfdb19

dashboard link: https://syzkaller.appspot.com/bug?extid=9e03a9535ea65f687a44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=1089ab3a580000

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

[Qing Wang]

#syz test

diff --git a/fs/namespace.c b/fs/namespace.c

index a67cbe42746d..d769d50de5d6 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5678,13 +5678,15 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,

s->mnt = mnt_file->f_path.mnt;
ns = real_mount(s->mnt)->mnt_ns;
- if (!ns)
+ if (IS_ERR_OR_NULL(ns)) {
/*
* We can't set mount point and mnt_ns_id since we don't have a
* ns for the mount. This can happen if the mount is unmounted

- * with MNT_DETACH.
+ * with MNT_DETACH or if it's an internal mount.

*/
s->mask &= ~(STATMOUNT_MNT_POINT | STATMOUNT_MNT_NS_ID);

[syzbot]

Hello,

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

Reported-by: syzbot+9e03a9...@syzkaller.appspotmail.com
Tested-by: syzbot+9e03a9...@syzkaller.appspotmail.com

Tested on:

commit: cee73b1e Merge tag 'riscv-for-linus-7.0-mw1' of git://..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=173eaf8a580000

kernel config: https://syzkaller.appspot.com/x/.config?x=fe62ec9519bfdb19
dashboard link: https://syzkaller.appspot.com/bug?extid=9e03a9535ea65f687a44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=1183615a580000

[Qing Wang]

#syz test

diff --git a/fs/namespace.c b/fs/namespace.c

index a67cbe42746d..eb7d2774ee1c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5678,13 +5678,16 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,

s->mnt = mnt_file->f_path.mnt;
ns = real_mount(s->mnt)->mnt_ns;
- if (!ns)

+ if (IS_ERR(ns))
+ return PTR_ERR(ns);

+ if (!ns) {

/*
* We can't set mount point and mnt_ns_id since we don't have a
* ns for the mount. This can happen if the mount is unmounted

* with MNT_DETACH.

*/
s->mask &= ~(STATMOUNT_MNT_POINT | STATMOUNT_MNT_NS_ID);
+ }

[syzbot]

Hello,

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

Reported-by: syzbot+9e03a9...@syzkaller.appspotmail.com
Tested-by: syzbot+9e03a9...@syzkaller.appspotmail.com

Tested on:

commit: cee73b1e Merge tag 'riscv-for-linus-7.0-mw1' of git://..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=1718be5a580000

kernel config: https://syzkaller.appspot.com/x/.config?x=fe62ec9519bfdb19
dashboard link: https://syzkaller.appspot.com/bug?extid=9e03a9535ea65f687a44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=13f6e652580000