general protection fault in vma_is

Based on kernel commit 95d10484d66e:

Root Cause Analysis

1. Involved Functions, Structs, and Files

Source Files: mm/gup.c, io_uring/rsrc.c, mm/shmem.c
Functions Involved:
- __gup_longterm_locked() (mm/gup.c)
- check_and_migrate_movable_pages() (mm/gup.c)
- pin_user_pages() (mm/gup.c)
- io_pin_pages() (io_uring/rsrc.c)
- vma_is_shmem() (mm/shmem.c)
Structs and Fields:
- struct vm_area_struct::vm_ops (mm/shmem.c)
- vmas array (struct vm_area_struct **) passed to GUP
- pages array (struct page **) passed to GUP

2. Technical Mechanism and Trigger Flow

Buffer Registration in io_uring: Userspace registers a user buffer via io_uring_register (IORING_REGISTER_BUFFERS). In io_uring/rsrc.c:io_pin_pages(), the kernel calculates the total number of pages required (nr_pages = end - start), allocates pages and vmas arrays of size nr_pages, and calls:
```
pret = pin_user_pages(ubuf, nr_pages, FOLL_WRITE | FOLL_LONGTERM, pages, vmas);
```

GUP Call Handling in mm/gup.c: pin_user_pages() passes the request to __gup_longterm_locked():

static long __gup_longterm_locked(struct mm_struct *mm,
                                  unsigned long start,
                                  unsigned long nr_pages,
                                  struct page **pages,
                                  struct vm_area_struct **vmas,
                                  unsigned int gup_flags)
{
    unsigned int flags;
    long rc;
...
    flags = memalloc_pin_save();
    do {
        rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
                                     NULL, gup_flags);
        if (rc <= 0)
            break;
        rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
    } while (rc == -EAGAIN);
    memalloc_pin_restore(flags);

    return rc ? rc : nr_pages;
}

Flawed Handling of Partial Pins:
- If the requested virtual address range spans across an unmapped region or hits a mapping error, __get_user_pages_locked() performs a partial pin and returns rc (where 0 < rc < nr_pages). In this scenario, only the first rc elements of pages[] and vmas[] are populated.
- check_and_migrate_movable_pages(rc, pages, gup_flags) is called on the rc pinned pages. If none of these pages need migration, it returns 0 (success).
- The defect: rc is overwritten with 0 (the return value of check_and_migrate_movable_pages()), discarding the actual count of pinned pages (rc).
- The loop condition while (rc == -EAGAIN) terminates because rc == 0.
- At line 2086, the function evaluates return rc ? rc : nr_pages;. Because rc == 0, it evaluates to nr_pages and returns the full requested count nr_pages, falsely claiming that all requested pages were successfully pinned.
Manifestation in Caller (io_pin_pages()):
- io_pin_pages() checks whether all pages were pinned:
```
if (pret == nr_pages) {
    for (i = 0; i < nr_pages; i++) {
        struct vm_area_struct *vma = vmas[i];

        if (vma_is_shmem(vma))
            continue;
        ...
    }
```
- Because pret == nr_pages evaluates to true, the loop iterates from 0 to nr_pages - 1.
- For index i >= rc, vmas[i] was never populated by GUP and remains NULL (or uninitialized).
- When vma_is_shmem(vma) is called with vma == NULL, it dereferences vma->vm_ops at offset 0x90 (return vma->vm_ops == &shmem_vm_ops;).
- Under KASAN, checking shadow memory for 0x90 (0xdffffc0000000012) traps with a General Protection Fault (KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097]).

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision
465f11a2	assessment-security	DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ✅ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌	❓	general protection fault in vma_is_shmem	2026/11/05 13:43	2026/11/05 13:43	2026/11/05 14:35	5cecaf1f
134b7c2e	assessment-security		💥	general protection fault in vma_is_shmem	2026/10/05 16:16	2026/10/05 16:16	2026/10/05 16:28	1995e6c7
0959373f	assessment-security		💥	general protection fault in vma_is_shmem	2026/09/04 11:49	2026/09/04 11:49	2026/09/04 12:04	801f0966
b7132c6b	assessment-security		💥	general protection fault in vma_is_shmem	2026/08/05 00:07	2026/08/05 00:07	2026/08/05 00:07	d4abbeac
d4c9cbb7	assessment-security		💥	general protection fault in vma_is_shmem	2026/07/05 09:14	2026/07/05 09:14	2026/07/05 09:27	93f57954
4604dec7	assessment-security		💥	general protection fault in vma_is_shmem	2026/06/18 08:47	2026/06/18 08:47	2026/06/18 09:01	b62b3ded
7995b269	assessment-security		💥	general protection fault in vma_is_shmem	2026/06/10 04:33	2026/06/10 04:33	2026/06/10 04:49	c36c07f6
2603e8a6	assessment-security		💥	general protection fault in vma_is_shmem	2026/06/04 07:57	2026/06/04 07:57	2026/06/04 08:10	62fe1528
5d9e0c59	assessment-security		💥	general protection fault in vma_is_shmem	2026/06/02 05:57	2026/06/02 05:57	2026/06/02 06:21	1095583b
3333dffc	assessment-security		💥	general protection fault in vma_is_shmem	2026/05/22 08:49	2026/05/22 08:49	2026/05/22 10:20	70ae9b03

assessment-security

DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ✅ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌

❓

general protection fault in vma_is_shmem

2026/11/05 13:43

2026/11/05 14:35

5cecaf1f

134b7c2e

assessment-security

💥

general protection fault in vma_is_shmem

2026/10/05 16:16

2026/10/05 16:28

1995e6c7

0959373f

assessment-security

💥

general protection fault in vma_is_shmem

2026/09/04 11:49

2026/09/04 12:04

801f0966

b7132c6b

assessment-security

💥

general protection fault in vma_is_shmem

2026/08/05 00:07

d4abbeac

d4c9cbb7

assessment-security

💥

general protection fault in vma_is_shmem

2026/07/05 09:14

2026/07/05 09:27

93f57954

4604dec7

assessment-security

💥

general protection fault in vma_is_shmem

2026/06/18 08:47

2026/06/18 09:01

b62b3ded

7995b269

assessment-security

💥

general protection fault in vma_is_shmem

2026/06/10 04:33

2026/06/10 04:49

c36c07f6

2603e8a6

assessment-security

💥

general protection fault in vma_is_shmem

2026/06/04 07:57

2026/06/04 08:10

62fe1528

5d9e0c59

assessment-security

💥

general protection fault in vma_is_shmem

2026/06/02 05:57

2026/06/02 06:21

1095583b

3333dffc

assessment-security

💥

general protection fault in vma_is_shmem

2026/05/22 08:49

2026/05/22 10:20

70ae9b03

Title	Replies (including bot)	Last reply
[syzbot] general protection fault in vma_is_shmem	5 (6)	2022/08/31 09:40

Title

Replies (including bot)

Last reply

[syzbot] general protection fault in vma_is_shmem

5 (6)

2022/08/31 09:40

general protection fault, probably for non-canonical address 0xdffffc0000000012: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000090-0x0000000000000097] CPU: 1 PID: 3607 Comm: syz-executor359 Not tainted 6.0.0-rc1-next-20220817-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022 RIP: 0010:vma_is_shmem+0x21/0x40 mm/shmem.c:254 Code: 73 02 e9 20 fc ff ff 66 90 53 48 89 fb e8 07 2c cf ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 81 bb 90 00 00 00 20 8f f7 89 5b 0f 94 c0 c3 RSP: 0018:ffffc900037cfb68 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000012 RSI: ffffffff81ace949 RDI: 0000000000000090 RBP: ffff888071b00720 R08: 0000000000000006 R09: 00000000000000e4 R10: 0000000000008001 R11: 0000000000000000 R12: 00000000000000e4 R13: ffff888071b00000 R14: dffffc0000000000 R15: 0000000000000000 FS: 0000555556ab5300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa3c8f13260 CR3: 00000000718f5000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> io_pin_pages+0x25f/0x430 io_uring/rsrc.c:1207 io_sqe_buffer_register+0x14e/0x13b0 io_uring/rsrc.c:1254 io_sqe_buffers_register.cold+0x351/0x445 io_uring/rsrc.c:1346 __io_uring_register io_uring/io_uring.c:3711 [inline] __do_sys_io_uring_register+0x96d/0x1110 io_uring/io_uring.c:3878 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f548fcdfbb9 Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 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 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffc644b88f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f548fcdfbb9 RDX: 0000000020000080 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 00007f548fca3d60 R08: 0000000010000000 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000246 R12: 00007f548fca3df0 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: ---[ end trace 0000000000000000 ]--- RIP: 0010:vma_is_shmem+0x21/0x40 mm/shmem.c:254 Code: 73 02 e9 20 fc ff ff 66 90 53 48 89 fb e8 07 2c cf ff 48 8d bb 90 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 10 48 81 bb 90 00 00 00 20 8f f7 89 5b 0f 94 c0 c3 RSP: 0018:ffffc900037cfb68 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000012 RSI: ffffffff81ace949 RDI: 0000000000000090 RBP: ffff888071b00720 R08: 0000000000000006 R09: 00000000000000e4 R10: 0000000000008001 R11: 0000000000000000 R12: 00000000000000e4 R13: ffff888071b00000 R14: dffffc0000000000 R15: 0000000000000000 FS: 0000555556ab5300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa3c8f13260 CR3: 00000000718f5000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 ---------------- Code disassembly (best guess): 0: 73 02 jae 0x4 2: e9 20 fc ff ff jmpq 0xfffffc27 7: 66 90 xchg %ax,%ax 9: 53 push %rbx a: 48 89 fb mov %rdi,%rbx d: e8 07 2c cf ff callq 0xffcf2c19 12: 48 8d bb 90 00 00 00 lea 0x90(%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: 75 10 jne 0x40 30: 48 81 bb 90 00 00 00 cmpq $0xffffffff89f78f20,0x90(%rbx) 37: 20 8f f7 89 3b: 5b pop %rbx 3c: 0f 94 c0 sete %al 3f: c3 retq

Crashes (28):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Manager	Title
2022/08/17 15:07	linux-next	95d10484d66e	4e72d229	.config	strace log	report	syz	C		ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/22 18:54	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/22 12:25	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/22 06:46	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/22 06:46	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/21 20:04	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/20 18:19	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/20 08:52	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/20 08:51	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 21:42	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 13:49	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 11:55	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 11:21	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 10:52	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 10:42	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/19 10:42	linux-next	8755ae45a9e8	26a13b38	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/18 15:58	linux-next	5b6a4bf680d6	d58e263f	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/18 15:36	linux-next	5b6a4bf680d6	d58e263f	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/18 11:46	linux-next	5b6a4bf680d6	d58e263f	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/18 10:53	linux-next	5b6a4bf680d6	d58e263f	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 21:33	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 21:33	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 12:35	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 11:52	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 10:02	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 08:27	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 08:22	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem
2022/08/17 06:06	linux-next	95d10484d66e	4e72d229	.config	console log	report			info	ci-upstream-linux-next-kasan-gce-root	general protection fault in vma_is_shmem

Crashes (28):

Assets (help?)

2022/08/17 15:07

linux-next