KASAN: use-after-free Read in filemap_fault

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6a1d293238c1 Add linux-next specific files for 20181224
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=102ca567400000
kernel config: https://syzkaller.appspot.com/x/.config?x=f9369d117d073843
dashboard link: https://syzkaller.appspot.com/bug?extid=b437b5a429d680cf2217
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15f059b3400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12ac602d400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b437b5...@syzkaller.appspotmail.com

sshd (8177) used greatest stack depth: 15720 bytes left
hrtimer: interrupt took 27544 ns
==================================================================
BUG: KASAN: use-after-free in filemap_fault+0x2818/0x2a70 mm/filemap.c:2559
Read of size 8 at addr ffff8881b15026b0 by task syz-executor997/8196

CPU: 0 PID: 8196 Comm: syz-executor997 Not tainted 4.20.0-rc7-next-20181224
#188
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1d3/0x2c6 lib/dump_stack.c:113
print_address_description.cold.5+0x9/0x1ff mm/kasan/report.c:187
kasan_report.cold.6+0x1b/0x39 mm/kasan/report.c:317
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
filemap_fault+0x2818/0x2a70 mm/filemap.c:2559
ext4_filemap_fault+0x82/0xad fs/ext4/inode.c:6326
__do_fault+0x176/0x6f0 mm/memory.c:3013
do_shared_fault mm/memory.c:3479 [inline]
do_fault mm/memory.c:3554 [inline]
handle_pte_fault mm/memory.c:3781 [inline]
__handle_mm_fault+0x373b/0x55f0 mm/memory.c:3905
handle_mm_fault+0x54f/0xc70 mm/memory.c:3942
do_user_addr_fault arch/x86/mm/fault.c:1475 [inline]
__do_page_fault+0x5f6/0xd70 arch/x86/mm/fault.c:1541
do_page_fault+0xf2/0x7e0 arch/x86/mm/fault.c:1572
page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1143
RIP: 0033:0x400a57
Code: 00 00 00 00 e8 ba 59 04 00 8b 03 85 c0 74 d8 c7 45 08 00 00 00 00 83
7d 04 05 0f 87 49 02 00 00 8b 45 04 ff 24 c5 e8 e4 4a 00 <c7> 04 25 fa ff
00 20 2e 2f 62 75 66 c7 04 25 fe ff 00 20 73 00 b9
RSP: 002b:00007f48cd9c0dc0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 00000000006dbc28 RCX: 0000000000446409
RDX: 0000000000446409 RSI: 0000000000000081 RDI: 00000000006dbc2c
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007ffd0bb6676f R14: 00007f48cd9c19c0 R15: 00000000006dbd2c

Allocated by task 8196:
save_stack+0x43/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
kasan_kmalloc+0xcb/0xd0 mm/kasan/common.c:482
kasan_slab_alloc+0x12/0x20 mm/kasan/common.c:397
kmem_cache_alloc+0x130/0x730 mm/slab.c:3541
vm_area_alloc+0x7a/0x1d0 kernel/fork.c:331
mmap_region+0x9d7/0x1cd0 mm/mmap.c:1756
do_mmap+0xa22/0x1230 mm/mmap.c:1559
do_mmap_pgoff include/linux/mm.h:2421 [inline]
vm_mmap_pgoff+0x213/0x2c0 mm/util.c:350
ksys_mmap_pgoff+0x4da/0x660 mm/mmap.c:1609
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:99 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:90 [inline]
__x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:90
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8197:
save_stack+0x43/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
__cache_free mm/slab.c:3485 [inline]
kmem_cache_free+0x83/0x290 mm/slab.c:3747
vm_area_free+0x1c/0x20 kernel/fork.c:350
remove_vma+0x13a/0x180 mm/mmap.c:185
remove_vma_list mm/mmap.c:2585 [inline]
__do_munmap+0x729/0xf50 mm/mmap.c:2822
do_munmap mm/mmap.c:2830 [inline]
mmap_region+0x6a7/0x1cd0 mm/mmap.c:1729
do_mmap+0xa22/0x1230 mm/mmap.c:1559
do_mmap_pgoff include/linux/mm.h:2421 [inline]
vm_mmap_pgoff+0x213/0x2c0 mm/util.c:350
ksys_mmap_pgoff+0x4da/0x660 mm/mmap.c:1609
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:99 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:90 [inline]
__x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:90
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881b1502670
which belongs to the cache vm_area_struct of size 200
The buggy address is located 64 bytes inside of
200-byte region [ffff8881b1502670, ffff8881b1502738)
The buggy address belongs to the page:
page:ffffea0006c54080 count:1 mapcount:0 mapping:ffff8881da9827c0
index:0xffff8881b1502eb0
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffffea0007477408 ffffea0006c5ec48 ffff8881da9827c0
raw: ffff8881b1502eb0 ffff8881b1502040 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881b1502580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881b1502600: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fb fb
> ffff8881b1502680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881b1502700: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fb
ffff8881b1502780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
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[Andrew Morton]

On Fri, 28 Dec 2018 12:51:04 -0800 syzbot <syzbot+b437b5...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following crash on:

uh-oh. Josef, could you please take a look?

: page = find_get_page(mapping, offset);
: if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
: /*
: * We found the page, so try async readahead before
: * waiting for the lock.
: */
: fpin = do_async_mmap_readahead(vmf, page);
: } else if (!page) {
: /* No page in the page cache at all */
: fpin = do_sync_mmap_readahead(vmf);
: count_vm_event(PGMAJFAULT);
: count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);

vmf->vma has been freed at this point.

: ret = VM_FAULT_MAJOR;
: retry_find:
: page = pagecache_get_page(mapping, offset,
: FGP_CREAT|FGP_FOR_MMAP,
: vmf->gfp_mask);
: if (!page) {
: if (fpin)
: goto out_retry;
: return vmf_error(-ENOMEM);
: }
: }

[Kirill A. Shutemov]

On Fri, Dec 28, 2018 at 12:51:04PM -0800, syzbot wrote:
> Allocated by task 8196:

...

> Freed by task 8197:

Hm. VMA allocated by one process (I don't see threads in the test case)
gets freed by another one. Looks fishy to me.

--
Kirill A. Shutemov

[Kirill A. Shutemov]

Ignore this. I need some to go sleep %)

--
Kirill A. Shutemov

[Kirill A. Shutemov]

Here's a fixup for "filemap: drop the mmap_sem for all blocking operations".

do_sync_mmap_readahead() drops mmap_sem now, so by the time of
dereferencing vmf->vma for count_memcg_event_mm() the VMA can be gone.

diff --git a/mm/filemap.c b/mm/filemap.c
index 00a9315f45d4..65c85c47bdb1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2554,10 +2554,10 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)

fpin = do_async_mmap_readahead(vmf, page);
} else if (!page) {
/* No page in the page cache at all */

- fpin = do_sync_mmap_readahead(vmf);

count_vm_event(PGMAJFAULT);
count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);

ret = VM_FAULT_MAJOR;
+ fpin = do_sync_mmap_readahead(vmf);

retry_find:
page = pagecache_get_page(mapping, offset,
FGP_CREAT|FGP_FOR_MMAP,

--
Kirill A. Shutemov

[Dmitry Vyukov]

If you are going to squash this, please add:

Tested-by: syzbot+b437b5...@syzkaller.appspotmail.com

> do_sync_mmap_readahead() drops mmap_sem now, so by the time of
> dereferencing vmf->vma for count_memcg_event_mm() the VMA can be gone.
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 00a9315f45d4..65c85c47bdb1 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2554,10 +2554,10 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> fpin = do_async_mmap_readahead(vmf, page);
> } else if (!page) {
> /* No page in the page cache at all */
> - fpin = do_sync_mmap_readahead(vmf);
> count_vm_event(PGMAJFAULT);
> count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
> ret = VM_FAULT_MAJOR;
> + fpin = do_sync_mmap_readahead(vmf);
> retry_find:
> page = pagecache_get_page(mapping, offset,
> FGP_CREAT|FGP_FOR_MMAP,
> --
> Kirill A. Shutemov
>

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