[syzbot] KASAN: use-after-free Read in do_sync_mmap_readahead

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3b5e1590a267 Merge tag 'gpio-fixes-for-v5.18' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ae2bfdf00000
kernel config: https://syzkaller.appspot.com/x/.config?x=d84df8e1a4c4d5a4
dashboard link: https://syzkaller.appspot.com/bug?extid=5b96d55e5b54924c77ad
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5b96d5...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in do_sync_mmap_readahead+0x465/0x9f0 mm/filemap.c:3006
Read of size 8 at addr ffff88801fedb050 by task syz-executor.5/1755

CPU: 0 PID: 1755 Comm: syz-executor.5 Not tainted 5.18.0-rc7-syzkaller-00136-g3b5e1590a267 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
print_address_description+0x65/0x4b0 mm/kasan/report.c:313
print_report+0xf4/0x210 mm/kasan/report.c:429
kasan_report+0xfb/0x130 mm/kasan/report.c:491
do_sync_mmap_readahead+0x465/0x9f0 mm/filemap.c:3006
filemap_fault+0x349/0xf20 mm/filemap.c:3138
__do_fault+0x139/0x4f0 mm/memory.c:3915
do_read_fault mm/memory.c:4240 [inline]
do_fault mm/memory.c:4369 [inline]
handle_pte_fault mm/memory.c:4627 [inline]
__handle_mm_fault mm/memory.c:4763 [inline]
handle_mm_fault+0x2bbb/0x3940 mm/memory.c:4861
faultin_page mm/gup.c:878 [inline]
__get_user_pages+0x4fd/0x1150 mm/gup.c:1099
populate_vma_page_range+0x216/0x2b0 mm/gup.c:1442
__mm_populate+0x2ea/0x4d0 mm/gup.c:1555
mm_populate include/linux/mm.h:2701 [inline]
vm_mmap_pgoff+0x241/0x2f0 mm/util.c:524
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1628
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7faf9f4890e9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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:00007fafa06c9168 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007faf9f59bf60 RCX: 00007faf9f4890e9
RDX: 0000000001000006 RSI: 0000000000b34900 RDI: 0000000020000000
RBP: 00007faf9f4e308d R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000028011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff03616e1f R14: 00007fafa06c9300 R15: 0000000000022000
</TASK>

Allocated by task 1755:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:436 [inline]
__kasan_slab_alloc+0xb2/0xe0 mm/kasan/common.c:469
kasan_slab_alloc include/linux/kasan.h:224 [inline]
slab_post_alloc_hook mm/slab.h:749 [inline]
slab_alloc_node mm/slub.c:3217 [inline]
slab_alloc mm/slub.c:3225 [inline]
__kmem_cache_alloc_lru mm/slub.c:3232 [inline]
kmem_cache_alloc+0x199/0x2f0 mm/slub.c:3242
vm_area_alloc+0x20/0xe0 kernel/fork.c:459
mmap_region+0xbef/0x1730 mm/mmap.c:1771
do_mmap+0x7a7/0xdf0 mm/mmap.c:1582
vm_mmap_pgoff+0x1e5/0x2f0 mm/util.c:519
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1628
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Freed by task 1759:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4c/0x70 mm/kasan/common.c:45
kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:370
____kasan_slab_free+0xd8/0x110 mm/kasan/common.c:366
kasan_slab_free include/linux/kasan.h:200 [inline]
slab_free_hook mm/slub.c:1728 [inline]
slab_free_freelist_hook+0x12e/0x1a0 mm/slub.c:1754
slab_free mm/slub.c:3510 [inline]
kmem_cache_free+0xc7/0x270 mm/slub.c:3527
remove_vma mm/mmap.c:189 [inline]
remove_vma_list mm/mmap.c:2625 [inline]
__do_munmap+0x1b4f/0x1cd0 mm/mmap.c:2863
do_munmap mm/mmap.c:2871 [inline]
munmap_vma_range mm/mmap.c:604 [inline]
mmap_region+0x97a/0x1730 mm/mmap.c:1746
do_mmap+0x7a7/0xdf0 mm/mmap.c:1582
vm_mmap_pgoff+0x1e5/0x2f0 mm/util.c:519
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1628
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

The buggy address belongs to the object at ffff88801fedb000
which belongs to the cache vm_area_struct of size 200
The buggy address is located 80 bytes inside of
200-byte region [ffff88801fedb000, ffff88801fedb0c8)

The buggy address belongs to the physical page:
page:ffffea00007fb6c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1fedb
memcg:ffff88801b6a0001
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 dead000000000100 dead000000000122 ffff888140006a00
raw: 0000000000000000 00000000000f000f 00000001ffffffff ffff88801b6a0001
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 20293, tgid 20293 (modprobe), ts 461559890566, free_ts 461429792689
prep_new_page mm/page_alloc.c:2441 [inline]
get_page_from_freelist+0x72e/0x7a0 mm/page_alloc.c:4182
__alloc_pages+0x26c/0x5f0 mm/page_alloc.c:5408
alloc_slab_page+0x70/0xf0 mm/slub.c:1799
allocate_slab+0x5e/0x560 mm/slub.c:1944
new_slab mm/slub.c:2004 [inline]
___slab_alloc+0x41e/0xcd0 mm/slub.c:3005
__slab_alloc mm/slub.c:3092 [inline]
slab_alloc_node mm/slub.c:3183 [inline]
slab_alloc mm/slub.c:3225 [inline]
__kmem_cache_alloc_lru mm/slub.c:3232 [inline]
kmem_cache_alloc+0x246/0x2f0 mm/slub.c:3242
vm_area_alloc+0x20/0xe0 kernel/fork.c:459
mmap_region+0xbef/0x1730 mm/mmap.c:1771
do_mmap+0x7a7/0xdf0 mm/mmap.c:1582
vm_mmap_pgoff+0x1e5/0x2f0 mm/util.c:519
ksys_mmap_pgoff+0x48c/0x6d0 mm/mmap.c:1628
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1356 [inline]
free_pcp_prepare+0x812/0x900 mm/page_alloc.c:1406
free_unref_page_prepare mm/page_alloc.c:3328 [inline]
free_unref_page_list+0x12c/0x890 mm/page_alloc.c:3460
release_pages+0x2a04/0x2cb0 mm/swap.c:980
__pagevec_release+0x7d/0xf0 mm/swap.c:1000
pagevec_release include/linux/pagevec.h:82 [inline]
folio_batch_release include/linux/pagevec.h:146 [inline]
truncate_inode_pages_range+0x4a2/0x17b0 mm/truncate.c:373
kill_bdev block/bdev.c:77 [inline]
blkdev_flush_mapping+0x181/0x350 block/bdev.c:656
blkdev_put_whole block/bdev.c:687 [inline]
blkdev_put+0x49f/0x790 block/bdev.c:947
blkdev_close+0x55/0x80 block/fops.c:512
__fput+0x3b9/0x820 fs/file_table.c:317
task_work_run+0x146/0x1c0 kernel/task_work.c:164
exit_task_work include/linux/task_work.h:37 [inline]
do_exit+0x547/0x1eb0 kernel/exit.c:795
do_group_exit+0x23b/0x2f0 kernel/exit.c:925
get_signal+0x172f/0x1780 kernel/signal.c:2864
arch_do_signal_or_restart+0x8d/0x750 arch/x86/kernel/signal.c:867
exit_to_user_mode_loop+0x74/0x160 kernel/entry/common.c:166
exit_to_user_mode_prepare+0xad/0x110 kernel/entry/common.c:201

Memory state around the buggy address:
ffff88801fedaf00: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc
ffff88801fedaf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801fedb000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801fedb080: fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc
ffff88801fedb100: fc fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[Andrew Morton]

On Wed, 25 May 2022 07:26:22 -0700 syzbot <syzbot+5b96d5...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 3b5e1590a267 Merge tag 'gpio-fixes-for-v5.18' of git://git..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15ae2bfdf00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d84df8e1a4c4d5a4
> dashboard link: https://syzkaller.appspot.com/bug?extid=5b96d55e5b54924c77ad
> compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5b96d5...@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in do_sync_mmap_readahead+0x465/0x9f0 mm/filemap.c:3006
> Read of size 8 at addr ffff88801fedb050 by task syz-executor.5/1755

A race?

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* Use the readahead code, even if readahead is disabled */
if (vmf->vma->vm_flags & VM_HUGEPAGE) {
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
ra->size = HPAGE_PMD_NR;
/*
* Fetch two PMD folios, so we get the chance to actually
* readahead, unless we've been told not to.
*/
--> if (!(vmf->vma->vm_flags & VM_RAND_READ))
ra->size *= 2;
ra->async_size = HPAGE_PMD_NR;
page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
return fpin;
}
#endif

Reading from vmf->vma->vm_flags was OK, then it suddenly wasn't.

[Matthew Wilcox]

On Wed, May 25, 2022 at 09:58:42AM -0700, Andrew Morton wrote:
> On Wed, 25 May 2022 07:26:22 -0700 syzbot <syzbot+5b96d5...@syzkaller.appspotmail.com> wrote:
> > BUG: KASAN: use-after-free in do_sync_mmap_readahead+0x465/0x9f0 mm/filemap.c:3006
> > Read of size 8 at addr ffff88801fedb050 by task syz-executor.5/1755
>
> A race?
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> /* Use the readahead code, even if readahead is disabled */
> if (vmf->vma->vm_flags & VM_HUGEPAGE) {
> fpin = maybe_unlock_mmap_for_io(vmf, fpin);
> ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
> ra->size = HPAGE_PMD_NR;
> /*
> * Fetch two PMD folios, so we get the chance to actually
> * readahead, unless we've been told not to.
> */
> --> if (!(vmf->vma->vm_flags & VM_RAND_READ))
> ra->size *= 2;
> ra->async_size = HPAGE_PMD_NR;
> page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
> return fpin;
> }
> #endif
>
> Reading from vmf->vma->vm_flags was OK, then it suddenly wasn't.

Ohh, that makes sense. We unlocked the mmap_sem, so the file is
pinned, but the VMA isn't. I'll whip up a patch.

[syzbot]

> On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote:
>>
>> Ohh, that makes sense. We unlocked the mmap_sem, so the file is
>> pinned, but the VMA isn't. I'll whip up a patch.
>

> #syz test

want 2 args (repo, branch), got 7

>
> From 01a4917c4cfe400eb310eba4f2fa466d381623c1 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <wi...@infradead.org>
> Date: Wed, 25 May 2022 14:23:45 -0400
> Subject: [PATCH] mm/filemap: Cache the value of vm_flags
>
> After we have unlocked the mmap_lock for I/O, the file is pinned, but
> the VMA is not. Checking this flag after that can be a use-after-free.
> It's not a terribly interesting use-after-free as it can only read one
> bit, and it's used to decide whether to read 2MB or 4MB. But it
> upsets the automated tools and it's generally bad practice anyway,
> so let's fix it.
>
> Reported-by: syzbot+5b96d5...@syzkaller.appspotmail.com
> Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings")
> Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>
> ---
> mm/filemap.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 9a1eef6c5d35..61dd39990fda 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2991,11 +2991,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
> struct address_space *mapping = file->f_mapping;
> DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
> struct file *fpin = NULL;
> + unsigned long vm_flags = vmf->vma->vm_flags;
> unsigned int mmap_miss;

>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> /* Use the readahead code, even if readahead is disabled */

> - if (vmf->vma->vm_flags & VM_HUGEPAGE) {
> + if (vm_flags & VM_HUGEPAGE) {

> fpin = maybe_unlock_mmap_for_io(vmf, fpin);
> ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
> ra->size = HPAGE_PMD_NR;

> @@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)

> * Fetch two PMD folios, so we get the chance to actually
> * readahead, unless we've been told not to.
> */

> - if (!(vmf->vma->vm_flags & VM_RAND_READ))
> + if (!(vm_flags & VM_RAND_READ))

> ra->size *= 2;
> ra->async_size = HPAGE_PMD_NR;
> page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);

> @@ -3012,12 +3013,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
> #endif
>
> /* If we don't want any read-ahead, don't bother */
> - if (vmf->vma->vm_flags & VM_RAND_READ)
> + if (vm_flags & VM_RAND_READ)
> return fpin;
> if (!ra->ra_pages)
> return fpin;
>
> - if (vmf->vma->vm_flags & VM_SEQ_READ) {
> + if (vm_flags & VM_SEQ_READ) {
> fpin = maybe_unlock_mmap_for_io(vmf, fpin);
> page_cache_sync_ra(&ractl, ra->ra_pages);
> return fpin;
> --
> 2.34.1
>

[Matthew Wilcox]

On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote:
>

> Ohh, that makes sense. We unlocked the mmap_sem, so the file is
> pinned, but the VMA isn't. I'll whip up a patch.

#syz test

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/* Use the readahead code, even if readahead is disabled */

- if (vmf->vma->vm_flags & VM_HUGEPAGE) {
+ if (vm_flags & VM_HUGEPAGE) {

fpin = maybe_unlock_mmap_for_io(vmf, fpin);
ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
ra->size = HPAGE_PMD_NR;

@@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)

* Fetch two PMD folios, so we get the chance to actually
* readahead, unless we've been told not to.
*/

- if (!(vmf->vma->vm_flags & VM_RAND_READ))
+ if (!(vm_flags & VM_RAND_READ))

ra->size *= 2;
ra->async_size = HPAGE_PMD_NR;
page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);

[syzbot]

> On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote:
>>
>> Ohh, that makes sense. We unlocked the mmap_sem, so the file is
>> pinned, but the VMA isn't. I'll whip up a patch.
>
> #syz test

want 2 args (repo, branch), got 7

>

> --
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[Andrew Morton]

On Wed, 25 May 2022 19:33:39 +0100 Matthew Wilcox <wi...@infradead.org> wrote:

> On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote:
> >
> > Ohh, that makes sense. We unlocked the mmap_sem, so the file is
> > pinned, but the VMA isn't. I'll whip up a patch.
>
> #syz test
>
> >From 01a4917c4cfe400eb310eba4f2fa466d381623c1 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <wi...@infradead.org>
> Date: Wed, 25 May 2022 14:23:45 -0400
> Subject: [PATCH] mm/filemap: Cache the value of vm_flags
>
> After we have unlocked the mmap_lock for I/O, the file is pinned, but
> the VMA is not. Checking this flag after that can be a use-after-free.
> It's not a terribly interesting use-after-free as it can only read one
> bit, and it's used to decide whether to read 2MB or 4MB. But it
> upsets the automated tools and it's generally bad practice anyway,
> so let's fix it.
>
> Reported-by: syzbot+5b96d5...@syzkaller.appspotmail.com
> Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings")
> Signed-off-by: Matthew Wilcox (Oracle) <wi...@infradead.org>

cc:stable also, please.

[Dmitry Vyukov]

On Wed, 25 May 2022 at 20:33, Matthew Wilcox <wi...@infradead.org> wrote:
>
> On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote:
> >
> > Ohh, that makes sense. We unlocked the mmap_sem, so the file is
> > pinned, but the VMA isn't. I'll whip up a patch.
>
> #syz test

This bug doesn't have a reproducer, so unfortunately it can't be tested.
But it would also need kernel repo/branch to apply the patch, e.g.
something like #syz test
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master