From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Yunseong Kim <yunseong.kim@est.tech>,
Namjae Jeon <linkinjeon@kernel.org>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15.y 4/5] ksmbd: validate ipc response length before dereferencing its fields
Date: Mon, 14 Sep 2026 14:43:49 -0400 [thread overview]
Message-ID: <20260914184350.571525-4-sashal@kernel.org> (raw)
In-Reply-To: <20260914184350.571525-1-sashal@kernel.org>
From: Yunseong Kim <yunseong.kim@est.tech>
[ Upstream commit e9b33376bd07bca4175f7bcc2d6034ef250f8181 ]
ipc_validate_msg() computes the expected message size by reading length
fields out of the response buffer supplied by the userspace ksmbd daemon
(payload_sz, session_key_len, ngroups, ...). Those fields are read before
the buffer is verified to be large enough to contain the struct they belong
to, so a short response makes the read land past the end of the allocation.
handle_response() sizes entry->response purely from the netlink attribute
length (nla_len()) and only guards the leading handle read, so the daemon
can install a response as small as the kmalloc-8 object seen below. When
ipc_msg_send_request() then calls ipc_validate_msg() for a
KSMBD_EVENT_RPC_REQUEST, the cast to struct ksmbd_rpc_command reads
resp->payload_sz at offset 8 of an 8-byte allocation:
[ 3697.841381] ==================================================================
[ 3697.844099] BUG: KASAN: slab-out-of-bounds in ipc_msg_send_request+0x763/0x800
[ 3697.846604] Read of size 4 at addr ffff888105f95910 by task kworker/4:3/20682
[ 3697.849061]
[ 3697.849801] CPU: 4 UID: 0 PID: 20682 Comm: kworker/4:3 Not tainted 7.2.0-rc3-next-20260717-virtme #117 PREEMPT(lazy)
[ 3697.850077] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 3697.850303] Workqueue: ksmbd-io handle_ksmbd_work
[ 3697.850592] Call Trace:
[ 3697.850794] <TASK>
[ 3697.850952] __dump_stack+0x21/0x60
[ 3697.851239] dump_stack_lvl+0xc2/0x100
[ 3697.851528] print_address_description+0x77/0x200
[ 3697.851816] ? ipc_msg_send_request+0x763/0x800
[ 3697.852024] print_report+0x58/0x70
[ 3697.852316] kasan_report+0x117/0x150
[ 3697.852585] ? down_write+0x146/0x1f0
[ 3697.852809] ? ipc_msg_send_request+0x763/0x800
[ 3697.853082] ipc_msg_send_request+0x763/0x800
[ 3697.853385] ? __pfx_ipc_msg_send_request+0x10/0x10
[ 3697.853604] ? kasan_unpoison+0x48/0x70
[ 3697.853936] ? __pfx___up_read+0x10/0x10
[ 3697.854221] ksmbd_rpc_ioctl+0x380/0x520
[ 3697.854542] ? __pfx_ksmbd_rpc_ioctl+0x10/0x10
[ 3697.854757] ? kasan_unpoison+0x48/0x70
[ 3697.854962] ? copy_from_kernel_nofault+0x32c/0x4e0
[ 3697.855166] ? kasan_unpoison+0x48/0x70
[ 3697.855416] fsctl_pipe_transceive+0x139/0x7a0
[ 3697.855705] ? __pfx_copy_from_kernel_nofault+0x10/0x10
[ 3697.855937] ? __pfx_fsctl_pipe_transceive+0x10/0x10
[ 3697.856388] ? __sanitizer_cov_trace_switch+0x7b/0x140
[ 3697.856620] smb2_ioctl+0x1141/0x3420
[ 3697.856994] ? __pfx_smb2_ioctl+0x10/0x10
[ 3697.857182] ? get_smb2_cmd_val+0xe3/0x1c0
[ 3697.857655] handle_ksmbd_work+0x9ad/0x15e0
[ 3697.858034] ? __pfx_handle_ksmbd_work+0x10/0x10
[ 3697.858251] ? lock_release+0xf7/0x360
[ 3697.858466] ? process_scheduled_works+0x954/0x1600
[ 3697.858698] ? process_scheduled_works+0x954/0x1600
[ 3697.858905] process_scheduled_works+0xc22/0x1600
[ 3697.859368] ? __pfx_process_scheduled_works+0x10/0x10
[ 3697.859637] ? __pfx_assign_work+0x10/0x10
[ 3697.859896] ? lock_is_held_type+0x7b/0x110
[ 3697.860146] worker_thread+0x975/0xee0
[ 3697.860524] ? __pfx_do_raw_spin_lock+0x10/0x10
[ 3697.860830] ? __kthread_parkme+0x21e/0x260
[ 3697.861105] kthread+0x3a6/0x490
[ 3697.861423] ? __pfx_worker_thread+0x10/0x10
[ 3697.861643] ? __pfx_kthread+0x10/0x10
[ 3697.861878] ret_from_fork+0x55a/0xa20
[ 3697.862194] ? __pfx_ret_from_fork+0x10/0x10
[ 3697.862480] ? __pfx_kthread+0x10/0x10
[ 3697.862714] ret_from_fork_asm+0x1a/0x30
[ 3697.862965] </TASK>
[ 3697.863039]
[ 3697.938882] Allocated by task 20761:
[ 3697.940257] kasan_save_track+0x3e/0x80
[ 3697.941782] __kasan_kmalloc+0x72/0x90
[ 3697.943228] __kvmalloc_node_noprof+0x3e9/0x6a0
[ 3697.944948] handle_generic_event+0x59b/0x750
[ 3697.946592] genl_family_rcv_msg_doit+0x3d6/0x560
[ 3697.946977] genl_rcv_msg+0x67c/0x900
[ 3697.947224] netlink_rcv_skb+0x286/0x580
[ 3697.947488] genl_rcv+0x2d/0x80
[ 3697.947706] netlink_unicast+0x937/0xb70
[ 3697.947993] netlink_sendmsg+0x977/0xc10
[ 3697.948268] __sock_sendmsg+0x264/0x2d0
[ 3697.948536] __sys_sendto+0x4de/0x690
[ 3697.948789] __x64_sys_sendto+0x173/0x380
[ 3697.949069] do_syscall_64+0x13d/0x420
[ 3697.949328] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 3697.949662]
[ 3697.949779] The buggy address belongs to the object at ffff888105f95908
[ 3697.949779] which belongs to the cache kmalloc-8 of size 8
[ 3697.950550] The buggy address is located 0 bytes to the right of
[ 3697.950550] allocated 8-byte region [ffff888105f95908, ffff888105f95910)
[ 3697.951455]
[ 3697.951574] The buggy address belongs to the physical page:
[ 3697.951958] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888105f951b8 pfn:0x105f95
[ 3697.952571] flags: 0x100000000000200(workingset|node=0|zone=2)
[ 3697.952973] page_type: f5(slab)
[ 3697.953198] raw: 0100000000000200 ffff888100042640 ffffea0004063610 ffff888100040588
[ 3697.953707] raw: ffff888105f951b8 00000000001c000e 00000000f5000000 0000000000000000
[ 3697.954240] page dumped because: kasan: bad access detected
[ 3697.954616]
[ 3697.954734] Memory state around the buggy address:
[ 3697.955063] ffff888105f95800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fa
[ 3697.955534] ffff888105f95880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.956006] >ffff888105f95900: fc 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.956477] ^
[ 3697.956728] ffff888105f95980: fc fc fc fa fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.957202] ffff888105f95a00: fc fc fc fc fc fa fc fc fc fc fc fc fc fc fc fc
[ 3697.957671] ==================================================================
The final "entry->msg_sz != msg_sz" comparison cannot help: the offending
read has already happened by the time it runs. Every case in the switch
shares this pattern.
Floor entry->msg_sz against the base struct of each event type before
dereferencing any of its length fields. On failure ipc_msg_send_request()
already frees the response and returns NULL, so callers stay safe.
The malformed message originates from the ksmbd.mountd daemon over genl
netlink rather than a remote SMB client, so triggering it requires a buggy
or compromised daemon; it is still an out-of-bounds read the validator is
meant to prevent.
Fixes: d6a6aa81eac2 ("ksmbd: validate response sizes in ipc_validate_msg()")
Signed-off-by: Yunseong Kim <yunseong.kim@est.tech>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ Stable dependency adaptation for f25e93768fcc5d8287e50b1ec52a42e4c276df34:
Retain the minimum response-header checks for RPC and SPNEGO before
dereferencing their variable-length fields in ipc_validate_msg().
The share-config header check is already present from dependency
2d1f4c041770, so it needs no additional change here.
Drop the extended-login hunk: this stable tree has neither
KSMBD_EVENT_LOGIN_REQUEST_EXT nor struct ksmbd_login_response_ext.
Do not introduce extended-login support or any new functions.
The target applies cleanly by three-way application to this tree. ]
Stable-dep-of: f25e93768fcc ("ksmbd: prevent out-of-bounds reads in share config responses")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ksmbd/transport_ipc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/ksmbd/transport_ipc.c b/fs/ksmbd/transport_ipc.c
index 12fa21bf84918..15ec5d8bd776b 100644
--- a/fs/ksmbd/transport_ipc.c
+++ b/fs/ksmbd/transport_ipc.c
@@ -469,6 +469,9 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry)
{
struct ksmbd_rpc_command *resp = entry->response;
+ if (entry->msg_sz < sizeof(struct ksmbd_rpc_command))
+ return -EINVAL;
+
if (check_add_overflow(sizeof(struct ksmbd_rpc_command),
resp->payload_sz, &msg_sz))
return -EINVAL;
@@ -478,6 +481,9 @@ static int ipc_validate_msg(struct ipc_msg_table_entry *entry)
{
struct ksmbd_spnego_authen_response *resp = entry->response;
+ if (entry->msg_sz < sizeof(struct ksmbd_spnego_authen_response))
+ return -EINVAL;
+
msg_sz = sizeof(struct ksmbd_spnego_authen_response) +
resp->session_key_len + resp->spnego_blob_len;
break;
--
2.53.0
next prev parent reply other threads:[~2026-09-14 18:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-14 11:03 FAILED: patch "[PATCH] ksmbd: prevent out-of-bounds reads in share config responses" failed to apply to 5.15-stable tree gregkh
2026-09-14 18:43 ` [PATCH 5.15.y 1/5] ksmbd: Use struct_size() to improve smb_direct_rdma_xmit() Sasha Levin
2026-09-14 18:43 ` [PATCH 5.15.y 2/5] ksmbd: use __GFP_RETRY_MAYFAIL Sasha Levin
2026-09-14 18:43 ` [PATCH 5.15.y 3/5] ksmbd: validate response sizes in ipc_validate_msg() Sasha Levin
2026-09-14 18:43 ` Sasha Levin [this message]
2026-09-14 18:43 ` [PATCH 5.15.y 5/5] ksmbd: prevent out-of-bounds reads in share config responses Sasha Levin
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