[syzbot] [mm?] KASAN: slab-use-after-free Read in finish_fault

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d35b2284e966 Add linux-next specific files for 20240607
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=178b77ba980000
kernel config: https://syzkaller.appspot.com/x/.config?x=d8bf5cd6bcca7343
dashboard link: https://syzkaller.appspot.com/bug?extid=d6e5c328862b5ae6cbfe
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=174c680a980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111b9696980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e0055a00a2cb/disk-d35b2284.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/192cbb8cf833/vmlinux-d35b2284.xz
kernel image: https://storage.googleapis.com/syzbot-assets/57804c9c9319/bzImage-d35b2284.xz

The issue was bisected to:

commit 1c05047ad01693ad92bdf8347fad3b5c2b25e8bb
Author: Baolin Wang <baoli...@linux.alibaba.com>
Date: Tue Jun 4 10:17:45 2024 +0000

mm: memory: extend finish_fault() to support large folio

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11267f94980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=13267f94980000
console output: https://syzkaller.appspot.com/x/log.txt?x=15267f94980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d6e5c3...@syzkaller.appspotmail.com
Fixes: 1c05047ad016 ("mm: memory: extend finish_fault() to support large folio")

==================================================================
BUG: KASAN: use-after-free in ptep_get include/linux/pgtable.h:317 [inline]
BUG: KASAN: use-after-free in ptep_get_lockless include/linux/pgtable.h:581 [inline]
BUG: KASAN: use-after-free in pte_range_none mm/memory.c:4409 [inline]
BUG: KASAN: use-after-free in finish_fault+0xf87/0x1460 mm/memory.c:4905
Read of size 8 at addr ffff88807bfb7000 by task syz-executor149/5117

CPU: 0 PID: 5117 Comm: syz-executor149 Not tainted 6.10.0-rc2-next-20240607-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:91 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:117
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x169/0x550 mm/kasan/report.c:488
kasan_report+0x143/0x180 mm/kasan/report.c:601
ptep_get include/linux/pgtable.h:317 [inline]
ptep_get_lockless include/linux/pgtable.h:581 [inline]
pte_range_none mm/memory.c:4409 [inline]
finish_fault+0xf87/0x1460 mm/memory.c:4905
do_read_fault mm/memory.c:5052 [inline]
do_fault mm/memory.c:5178 [inline]
do_pte_missing mm/memory.c:3948 [inline]
handle_pte_fault+0x3db5/0x7130 mm/memory.c:5502
__handle_mm_fault mm/memory.c:5645 [inline]
handle_mm_fault+0x10df/0x1ba0 mm/memory.c:5810
faultin_page mm/gup.c:1339 [inline]
__get_user_pages+0x6ef/0x1590 mm/gup.c:1638
populate_vma_page_range+0x264/0x330 mm/gup.c:2078
__mm_populate+0x27a/0x460 mm/gup.c:2181
mm_populate include/linux/mm.h:3442 [inline]
__do_sys_remap_file_pages mm/mmap.c:3177 [inline]
__se_sys_remap_file_pages+0x7a1/0x9a0 mm/mmap.c:3103
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: 0033:0x7ff1cbb3e399
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff1cbad8238 EFLAGS: 00000246 ORIG_RAX: 00000000000000d8
RAX: ffffffffffffffda RBX: 00007ff1cbbc8318 RCX: 00007ff1cbb3e399
RDX: 0000000000000000 RSI: 0000000000200000 RDI: 00000000202ec000
RBP: 00007ff1cbbc8310 R08: 0000000000000000 R09: 00007ff1cbad86c0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff1cbbc831c
R13: 0000000000000000 R14: 00007ffcff8e0350 R15: 00007ffcff8e0438
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7bfb7
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea00007ed408 ffff8880b94448a0 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_COMP|__GFP_ZERO), pid 5097, tgid 5088 (syz-executor149), ts 55842453591, free_ts 55925905863
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1470
prep_new_page mm/page_alloc.c:1478 [inline]
get_page_from_freelist+0x2cbd/0x2d70 mm/page_alloc.c:3457
__alloc_pages_noprof+0x256/0x6c0 mm/page_alloc.c:4715
alloc_pages_mpol_noprof+0x3e8/0x680 mm/mempolicy.c:2263
pagetable_alloc_noprof include/linux/mm.h:2881 [inline]
__pte_alloc_one_noprof include/asm-generic/pgalloc.h:70 [inline]
pte_alloc_one+0x88/0x5d0 arch/x86/mm/pgtable.c:33
do_fault_around mm/memory.c:5000 [inline]
do_read_fault mm/memory.c:5039 [inline]
do_fault mm/memory.c:5178 [inline]
do_pte_missing mm/memory.c:3948 [inline]
handle_pte_fault+0x2ba7/0x7130 mm/memory.c:5502
__handle_mm_fault mm/memory.c:5645 [inline]
handle_mm_fault+0x10df/0x1ba0 mm/memory.c:5810
faultin_page mm/gup.c:1339 [inline]
__get_user_pages+0x6ef/0x1590 mm/gup.c:1638
populate_vma_page_range+0x264/0x330 mm/gup.c:2078
__mm_populate+0x27a/0x460 mm/gup.c:2181
mm_populate include/linux/mm.h:3442 [inline]
__do_sys_remap_file_pages mm/mmap.c:3177 [inline]
__se_sys_remap_file_pages+0x7a1/0x9a0 mm/mmap.c:3103
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
page last free pid 5097 tgid 5088 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1089 [inline]
free_unref_folios+0x103a/0x1b00 mm/page_alloc.c:2669
folios_put_refs+0x76e/0x860 mm/swap.c:1020
free_pages_and_swap_cache+0x5c8/0x690 mm/swap_state.c:335
__tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
tlb_flush_mmu+0x3a3/0x680 mm/mmu_gather.c:373
tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:465
exit_mmap+0x44f/0xc80 mm/mmap.c:3395
__mmput+0x115/0x390 kernel/fork.c:1341
exit_mm+0x220/0x310 kernel/exit.c:565
do_exit+0x9aa/0x28e0 kernel/exit.c:861
do_group_exit+0x207/0x2c0 kernel/exit.c:1023
get_signal+0x16a1/0x1740 kernel/signal.c:2909
arch_do_signal_or_restart+0x96/0x830 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0xc9/0x370 kernel/entry/common.c:218
do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88807bfb6f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88807bfb6f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88807bfb7000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88807bfb7080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88807bfb7100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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[Baolin Wang]

Thanks for reporting. I think the problem is I should also consider the
pagetable of PMD size in case the pte entry overflows. I will fix this
issue ASAP.

[Baolin Wang]

I create following fix to avoid beyonding the PMD pagetable size.

diff --git a/mm/memory.c b/mm/memory.c
index 54d7d2acdf39..92c61800dfb4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4878,13 +4878,16 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
pgoff_t idx = folio_page_idx(folio, page);
/* The page offset of vmf->address within the VMA. */
pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
+ /* The index of the entry in the pagetable for fault
page. */
+ pgoff_t pte_off = pte_index(vmf->address);

/*
* Fallback to per-page fault in case the folio size in
page
- * cache beyond the VMA limits.
+ * cache beyond the VMA limits and PMD pagetable limits.
*/
if (unlikely(vma_off < idx ||
- vma_off + (nr_pages - idx) > vma_pages(vma))) {
+ vma_off + (nr_pages - idx) > vma_pages(vma) ||
+ pte_off < idx || pte_off + (nr_pages - idx)
> PTRS_PER_PTE - 1)) {
nr_pages = 1;
} else {
/* Now we can set mappings for the whole large
folio. */