KASAN: slab-out-of-bounds Read in md5_blocks

Status: upstream: reported C repro on 2026/10/01 23:29
Subsystems: ecryptfs
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+46bbbe175b7eea8036b8@syzkaller.appspotmail.com
First crash: 4d01h, last: 3d01h
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ID Workflow Result Correct Bug Created Started Finished Revision
8d8abdcf assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-out-of-bounds Read in md5_blocks 2026/09/29 03:25 2026/09/29 03:25 2026/09/29 04:15 58f15308
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[syzbot] [ecryptfs?] KASAN: slab-out-of-bounds Read in md5_blocks 0 (1) 2026/10/01 23:29

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in md5_block lib/crypto/md5.c:40 [inline]
BUG: KASAN: slab-out-of-bounds in md5_blocks+0x120/0xbd0 lib/crypto/md5.c:126
Read of size 64 at addr ffff88803236dce0 by task syz.1.18/5953

CPU: 0 UID: 0 PID: 5953 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trac
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 md5_block lib/crypto/md5.c:40 [inline]
 md5_blocks+0x120/0xbd0 lib/crypto/md5.c:126
 md5_update+0xef/0x150 lib/crypto/md5.c:161
 md5+0xed/0x180 lib/crypto/md5.c:202
 ecryptfs_write_tag_70_packet+0x820/0x12e0 fs/ecryptfs/keystore.c:741
 ecryptfs_encrypt_filename fs/ecryptfs/crypto.c:1378 [inline]
 ecryptfs_encrypt_and_encode_filename+0x576/0x1580 fs/ecryptfs/crypto.c:1789
 ecryptfs_lookup+0x20e/0x780 fs/ecryptfs/inode.c:402
 lookup_one_qstr_excl+0x12d/0x360 fs/namei.c:1810
 __start_dirop fs/namei.c:2920 [inline]
 start_dirop fs/namei.c:2942 [inline]
 filename_create+0x20e/0x370 fs/namei.c:5103
 filename_mkdirat+0xd2/0x510 fs/namei.c:5449
 __do_sys_mkdirat fs/namei.c:5477 [inline]
 __se_sys_mkdirat+0x35/0x150 fs/namei.c:5474
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe5ba99e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeb47b2408 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007fe5bac25fa0 RCX: 00007fe5ba99e159
RDX: 0000000000000080 RSI: 0000200000000100 RDI: 0000000000000003
RBP: 00007fe5baa3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe5bac25fac R14: 00007fe5bac25fa0 R15: 00007fe5bac25fa0
 </TASK>

Allocated by task 5953:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:409 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:426
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5531 [inline]
 __kmalloc_flags_noprof+0x52d/0x790 mm/slub.c:5719
 _kmalloc_flags_noprof mm/slab.h:55 [inline]
 __alloc_empty_sheaf+0x28/0x40 mm/slub.c:2854
 alloc_empty_sheaf mm/slub.c:2874 [inline]
 __pcs_replace_empty_main+0x43b/0x6c0 mm/slub.c:4806
 alloc_from_pcs mm/slub.c:4887 [inline]
 slab_alloc_node mm/slub.c:5021 [inline]
 kmem_cache_alloc_noprof+0x394/0x600 mm/slub.c:5047
 ecryptfs_init_fs_context+0x70/0x1b0 fs/ecryptfs/main.c:617
 alloc_fs_context+0x99e/0xd00 fs/fs_context.c:295
 do_new_mount+0x17f/0xdc0 fs/namespace.c:3841
 do_mount fs/namespace.c:4194 [inline]
 __do_sys_mount fs/namespace.c:4407 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4384
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88803236dc00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 224 bytes inside of
 allocated 256-byte region [ffff88803236dc00, ffff88803236dd00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3236c
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ff22b40 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813ff22b40 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffffffffffff81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 29, tgid 29 (kdevtmpfs), ts 16571924726
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1854
 prep_new_page mm/page_alloc.c:1862 [inline]
 get_page_from_freelist+0x220f/0x2280 mm/page_alloc.c:3933
 __alloc_frozen_pages_noprof+0x1fc/0x400 mm/page_alloc.c:5441
 alloc_slab_page mm/slub.c:3384 [inline]
 allocate_slab+0x7d/0x5e0 mm/slub.c:3499
 new_slab mm/slub.c:3550 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7539
 refill_sheaf mm/slub.c:2917 [inline]
 __pcs_replace_empty_main+0x2c8/0x6c0 mm/slub.c:4811
 alloc_from_pcs mm/slub.c:4887 [inline]
 slab_alloc_node mm/slub.c:5021 [inline]
 __do_kmalloc_node mm/slub.c:5530 [inline]
 __kmalloc_noprof+0x476/0x710 mm/slub.c:5556
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kmalloc_array_noprof include/linux/slab.h:1211 [inline]
 security_inode_init_security+0x102/0x3e0 security/security.c:1386
 shmem_mknod+0x1ea/0x340 mm/shmem.c:4042
 vfs_mknod+0x448/0x610 fs/namei.c:5282
 handle_create drivers/base/devtmpfs.c:283 [inline]
 handle drivers/base/devtmpfs.c:435 [inline]
 devtmpfs_work_loop+0x861/0xdf0 drivers/base/devtmpfs.c:450
 devtmpfsd+0x4d/0x50 drivers/base/devtmpfs.c:492
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88803236dc00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88803236dc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88803236dd00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff88803236dd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88803236de00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/28 23:27 linux-next 6375e61c01e9 a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-out-of-bounds Read in md5_blocks
2026/09/27 23:27 upstream d266640c6c76 a3c7249d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in md5_blocks
2026/09/27 23:27 upstream d266640c6c76 a3c7249d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in md5_blocks
2026/09/27 23:27 upstream d266640c6c76 a3c7249d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in md5_blocks
2026/09/27 23:27 upstream d266640c6c76 a3c7249d .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-out-of-bounds Read in md5_blocks
2026/09/28 22:22 linux-next 6375e61c01e9 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-out-of-bounds Read in md5_blocks
* Struck through repros no longer work on HEAD.