ksmbd: fix slab-out-of-bounds read in ksmbd_alloc_user()

ksmbd_alloc_user() copies resp->hash_sz bytes out of the mountd IPC
login response with

	user->passkey_sz = resp->hash_sz;
	user->passkey = kmalloc(resp->hash_sz, KSMBD_DEFAULT_GFP);
	if (user->passkey)
		memcpy(user->passkey, resp->hash, resp->hash_sz);

resp->hash_sz is a __u16 supplied by the response, but resp->hash[] is
only KSMBD_REQ_MAX_HASH_SZ bytes.  A malformed or malicious login
response can set hash_sz well beyond that (up to 65535), so the memcpy()
reads past the end of the response object.  ipc_validate_msg() does not
bound hash_sz, so reject any response whose hash_sz exceeds the on-stack
hash[] buffer before allocating and copying.

[ 2030.238706] BUG: KASAN: slab-out-of-bounds in ksmbd_alloc_user+0x278/0x680
[ 2030.240549] Read of size 65535 at addr ffff888121bb6680 by task kworker/4:1/18611
[ 2030.242296]
[ 2030.242710] CPU: 4 UID: 0 PID: 18611 Comm: kworker/4:1 Not tainted 7.1.0-next-20260623-virtme #96 PREEMPT(lazy)
[ 2030.242732] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 2030.242743] Workqueue: ksmbd-io handle_ksmbd_work
[ 2030.242763] Call Trace:
[ 2030.242769]  <TASK>
[ 2030.242776]  dump_stack_lvl+0xa2/0xd0
[ 2030.242794]  print_address_description+0x77/0x200
[ 2030.242815]  ? ksmbd_alloc_user+0x278/0x680
[ 2030.242831]  print_report+0x58/0x70
[ 2030.242848]  kasan_report+0x117/0x150
[ 2030.242869]  ? ksmbd_alloc_user+0x278/0x680
[ 2030.242888]  kasan_check_range+0x3c7/0x3f0
[ 2030.242908]  ? ksmbd_alloc_user+0x278/0x680
[ 2030.242925]  __asan_memcpy+0x29/0x70
[ 2030.242942]  ksmbd_alloc_user+0x278/0x680
[ 2030.242960]  ksmbd_login_user+0xc3/0x120
[ 2030.242978]  ntlm_authenticate+0x5e6/0x1b00
[ 2030.243017]  ? __pfx_ntlm_authenticate+0x10/0x10
[ 2030.243035]  ? ksmbd_session_lookup+0x188/0x1d0
[ 2030.243054]  ? __pfx_ksmbd_session_lookup+0x10/0x10
[ 2030.243090]  ? __sanitizer_cov_trace_switch+0x7b/0x140
[ 2030.243108]  smb2_sess_setup+0x1e4a/0x27b0
[ 2030.243126]  ? copy_from_kernel_nofault+0x199/0x300
[ 2030.243156]  ? __pfx_smb2_sess_setup+0x10/0x10
[ 2030.243173]  ? get_smb2_cmd_val+0xe3/0x1c0
[ 2030.243208]  handle_ksmbd_work+0x954/0x1280
[ 2030.243230]  ? __pfx_handle_ksmbd_work+0x10/0x10
[ 2030.243249]  ? process_scheduled_works+0xa07/0x1490
[ 2030.243270]  ? process_scheduled_works+0xa07/0x1490
[ 2030.243291]  process_scheduled_works+0xa70/0x1490
[ 2030.243320]  ? __pfx_process_scheduled_works+0x10/0x10
[ 2030.243340]  ? do_raw_spin_lock+0x130/0x300
[ 2030.243358]  ? lock_is_held_type+0x7b/0x110
[ 2030.243388]  worker_thread+0x932/0xe20
[ 2030.243415]  kthread+0x38a/0x470
[ 2030.243431]  ? __pfx_worker_thread+0x10/0x10
[ 2030.243451]  ? __pfx_kthread+0x10/0x10
[ 2030.243467]  ret_from_fork+0x484/0x910
[ 2030.243485]  ? __pfx_ret_from_fork+0x10/0x10
[ 2030.243501]  ? __switch_to+0xc77/0x12c0
[ 2030.243523]  ? __pfx_kthread+0x10/0x10
[ 2030.243540]  ret_from_fork_asm+0x1a/0x30
[ 2030.243564]  </TASK>
[ 2030.243570]
[ 2030.290164] Allocated by task 19279:
[ 2030.290911]  kasan_save_track+0x3e/0x80
[ 2030.292179]  __kasan_kmalloc+0x72/0x90
[ 2030.293217]  __kvmalloc_node_noprof+0x3ff/0x6b0
[ 2030.294467]  handle_generic_event+0x59b/0x750
[ 2030.295345]  genl_family_rcv_msg_doit+0x238/0x340
[ 2030.296553]  genl_rcv_msg+0x606/0x7b0
[ 2030.297129]  netlink_rcv_skb+0x22b/0x4a0
[ 2030.298500]  genl_rcv+0x2d/0x40
[ 2030.299273]  netlink_unicast+0x7ba/0x930
[ 2030.300019]  netlink_sendmsg+0x8c3/0xb00
[ 2030.301073]  __sock_sendmsg+0xec/0x140
[ 2030.301579]  __sys_sendto+0x357/0x470
[ 2030.302255]  __x64_sys_sendto+0xe3/0x100
[ 2030.303425]  do_syscall_64+0x135/0x460
[ 2030.304763]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 2030.305594]
[ 2030.305819] The buggy address belongs to the object at ffff888121bb6640
[ 2030.305819]  which belongs to the cache kmalloc-192 of size 192
[ 2030.309595] The buggy address is located 64 bytes inside of
[ 2030.309595]  allocated 166-byte region [ffff888121bb6640, ffff888121bb66e6)
[ 2030.312484]
[ 2030.312719] The buggy address belongs to the physical page:
[ 2030.314315] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x121bb6
[ 2030.316481] head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 2030.318248] flags: 0x100000000000040(head|node=0|zone=2)
[ 2030.319662] page_type: f5(slab)
[ 2030.320242] raw: 0100000000000040 ffff8881000424c0 ffffea00047c1510 ffff888100040468
[ 2030.321911] raw: 0000000000000000 0000000000150015 00000000f5000000 0000000000000000
[ 2030.324413] head: 0100000000000040 ffff8881000424c0 ffffea00047c1510 ffff888100040468
[ 2030.326150] head: 0000000000000000 0000000000150015 00000000f5000000 0000000000000000
[ 2030.327960] head: 0100000000000001 ffffffffffffff81 00000000ffffffff 00000000ffffffff
[ 2030.329615] head: ffff888121bb7ab0 0000000000000000 00000000ffffffff 0000000000000000
[ 2030.331861] page dumped because: kasan: bad access detected
[ 2030.332946]
[ 2030.333502] Memory state around the buggy address:
[ 2030.334698]  ffff888121bb6580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 2030.336475]  ffff888121bb6600: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
[ 2030.338143] >ffff888121bb6680: 00 00 00 00 00 00 00 00 00 00 00 00 06 fc fc fc
[ 2030.339116]                                                        ^
[ 2030.341315]  ffff888121bb6700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 2030.342801]  ffff888121bb6780: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
[ 2030.344643] ==================================================================

Found with ksmbdzzer [2], a KSMBD fuzzer that drives libFuzzer with a
kcov-dataflow [1] coverage vector: it folds each instrumented
comparison/argument's runtime operand value together with its PC (the
default arm mixes them as pc⊕val) so that a new operand value at a known
site counts as new coverage.

[1] https://lwn.net/Articles/1077606/
[2] https://github.com/yskzalloc/kcov-dataflow

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Yunseong Kim <yunseong.kim@est.tech>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions