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KASAN: slab-out-of-bounds Read in folio_try_get

Status: upstream: reported C repro on 2025/02/14 19:59
Subsystems: mm bcachefs
[Documentation on labels]
Reported-by: syzbot+2110ef46097c323451eb@syzkaller.appspotmail.com
First crash: 6d22h, last: 2d02h
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [mm?] [bcachefs?] KASAN: slab-out-of-bounds Read in folio_try_get 2 (3) 2025/02/14 20:57

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: slab-out-of-bounds in atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
BUG: KASAN: slab-out-of-bounds in page_ref_count include/linux/page_ref.h:67 [inline]
BUG: KASAN: slab-out-of-bounds in page_ref_add_unless include/linux/page_ref.h:237 [inline]
BUG: KASAN: slab-out-of-bounds in folio_ref_add_unless include/linux/page_ref.h:248 [inline]
BUG: KASAN: slab-out-of-bounds in folio_try_get+0xde/0x350 include/linux/page_ref.h:264
Read of size 4 at addr ffff88804f904b34 by task syz-executor127/5388

CPU: 0 UID: 0 PID: 5388 Comm: syz-executor127 Not tainted 6.14.0-rc2-syzkaller-00056-gab68d7eb7b1a #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:489
 kasan_report+0x143/0x180 mm/kasan/report.c:602
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
 page_ref_count include/linux/page_ref.h:67 [inline]
 page_ref_add_unless include/linux/page_ref.h:237 [inline]
 folio_ref_add_unless include/linux/page_ref.h:248 [inline]
 folio_try_get+0xde/0x350 include/linux/page_ref.h:264
 filemap_get_entry+0x240/0x3b0 mm/filemap.c:1870
 shmem_get_folio_gfp+0x285/0x1840 mm/shmem.c:2446
 shmem_get_folio mm/shmem.c:2628 [inline]
 shmem_write_begin+0x165/0x350 mm/shmem.c:3278
 generic_perform_write+0x346/0x990 mm/filemap.c:4189
 shmem_file_write_iter+0xf9/0x120 mm/shmem.c:3454
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0xacf/0xd10 fs/read_write.c:679
 ksys_write+0x18f/0x2b0 fs/read_write.c:731
 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: 0033:0x7fb60d00ef1f
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 19 81 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 6c 81 02 00 48
RSP: 002b:00007fb60c7b9fb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fb60c7b9ff0 RCX: 00007fb60d00ef1f
RDX: 0000000001000000 RSI: 00007fb604200000 RDI: 0000000000000003
RBP: 00007fb60d0976e0 R08: 0000000000000000 R09: 000000000000590c
R10: 0000000000000002 R11: 0000000000000293 R12: 00007fb60d0976ec
R13: 00007fb60c7ba030 R14: 0000000000000003 R15: 00007ffe9f1d73d8
 </TASK>

The buggy address belongs to the object at ffff88804f904b00
 which belongs to the cache radix_tree_node of size 576
The buggy address is located 52 bytes inside of
 allocated 576-byte region [ffff88804f904b00, ffff88804f904d40)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4f904
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88804054b581
flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff88801ac4fdc0 dead000000000122 0000000000000000
raw: 0000000000000000 00000000800b000b 00000000f5000000 ffff88804054b581
head: 04fff00000000040 ffff88801ac4fdc0 dead000000000122 0000000000000000
head: 0000000000000000 00000000800b000b 00000000f5000000 ffff88804054b581
head: 04fff00000000001 ffffea00013e4101 ffffffffffffffff 0000000000000000
head: 0000000000000002 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Reclaimable, gfp_mask 0x52810(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_RECLAIMABLE), pid 5382, tgid 5381 (syz-executor127), ts 127092553802, free_ts 126870415360
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0x365c/0x37a0 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x292/0x710 mm/page_alloc.c:4739
 alloc_pages_mpol+0x311/0x660 mm/mempolicy.c:2270
 alloc_slab_page mm/slub.c:2423 [inline]
 allocate_slab+0x8f/0x3a0 mm/slub.c:2587
 new_slab mm/slub.c:2640 [inline]
 ___slab_alloc+0xc27/0x14a0 mm/slub.c:3826
 __slab_alloc+0x58/0xa0 mm/slub.c:3916
 __slab_alloc_node mm/slub.c:3991 [inline]
 slab_alloc_node mm/slub.c:4152 [inline]
 kmem_cache_alloc_lru_noprof+0x26c/0x390 mm/slub.c:4183
 xas_alloc lib/xarray.c:377 [inline]
 xas_create+0x10d0/0x1ae0 lib/xarray.c:684
 xas_store+0x96/0x1870 lib/xarray.c:794
 shmem_add_to_page_cache+0x89d/0xcc0 mm/shmem.c:897
 shmem_alloc_and_add_folio+0x968/0x1090 mm/shmem.c:1928
 shmem_get_folio_gfp+0x621/0x1840 mm/shmem.c:2522
 shmem_get_folio mm/shmem.c:2628 [inline]
 shmem_write_begin+0x165/0x350 mm/shmem.c:3278
 generic_perform_write+0x346/0x990 mm/filemap.c:4189
 shmem_file_write_iter+0xf9/0x120 mm/shmem.c:3454
page last free pid 5392 tgid 5392 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 __free_pages_ok+0xbbf/0xe40 mm/page_alloc.c:1271
 __folio_put+0x2b3/0x360 mm/swap.c:112
 folio_put include/linux/mm.h:1489 [inline]
 free_large_kmalloc+0xfe/0x180 mm/slub.c:4728
 kfree+0x212/0x430 mm/slub.c:4751
 btree_bounce_free fs/bcachefs/btree_io.c:111 [inline]
 bch2_btree_node_read_done+0x3b1f/0x5f70 fs/bcachefs/btree_io.c:1243
 btree_node_read_work+0x6dc/0x1380 fs/bcachefs/btree_io.c:1358
 bch2_btree_node_read+0x2433/0x29f0
 bch2_btree_node_fill+0xca6/0x1370 fs/bcachefs/btree_cache.c:993
 bch2_btree_node_get_noiter+0x9d5/0xf70 fs/bcachefs/btree_cache.c:1260
 found_btree_node_is_readable fs/bcachefs/btree_node_scan.c:84 [inline]
 try_read_btree_node fs/bcachefs/btree_node_scan.c:213 [inline]
 read_btree_nodes_worker+0x1355/0x21f0 fs/bcachefs/btree_node_scan.c:262
 kthread+0x7a9/0x920 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Memory state around the buggy address:
 ffff88804f904a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88804f904a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88804f904b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                     ^
 ffff88804f904b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88804f904c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/14 06:56 upstream ab68d7eb7b1a d9a046cf .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in folio_try_get
2025/02/19 02:29 upstream 6537cfb395f3 9a14138f .config console log report syz / log [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro] ci-snapshot-upstream-root KASAN: wild-memory-access Read in folio_try_get
* Struck through repros no longer work on HEAD.