[PATCH 7.0 27/42] ksmbd: validate response sizes in ipc_validate_msg()

Greg Kroah-Hartman
2026-04-24T13:33:05Z

From: Michael Bommarito <michael.bommarito@gmail.com>

commit d6a6aa81eac2c9bff66dc6e191179cb69a14426b upstream.

ipc_validate_msg() computes the expected message size for each
response type by adding (or multiplying) attacker-controlled fields
from the daemon response to a fixed struct size in unsigned int
arithmetic. Three cases can overflow:

KSMBD_EVENT_RPC_REQUEST:
msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz;
KSMBD_EVENT_SHARE_CONFIG_REQUEST:
msg_sz = sizeof(struct ksmbd_share_config_response) +
resp->payload_sz;
KSMBD_EVENT_LOGIN_REQUEST_EXT:
msg_sz = sizeof(struct ksmbd_login_response_ext) +
resp->ngroups * sizeof(gid_t);

resp->payload_sz is __u32 and resp->ngroups is __s32. Each addition
can wrap in unsigned int; the multiplication by sizeof(gid_t) mixes
signed and size_t, so a negative ngroups is converted to SIZE_MAX
before the multiply. A wrapped value of msg_sz that happens to
equal entry->msg_sz bypasses the size check on the next line, and
downstream consumers (smb2pdu.c:6742 memcpy using rpc_resp->payload_sz,
kmemdup in ksmbd_alloc_user using resp_ext->ngroups) then trust the
unverified length.

Use check_add_overflow() on the RPC_REQUEST and SHARE_CONFIG_REQUEST
paths to detect integer overflow without constraining functional
payload size; userspace ksmbd-tools grows NDR responses in 4096-byte
chunks for calls like NetShareEnumAll, so a hard transport cap is
unworkable on the response side. For LOGIN_REQUEST_EXT, reject
resp->ngroups outside the signed [0, NGROUPS_MAX] range up front and
report the error from ipc_validate_msg() so it fires at the IPC
boundary; with that bound the subsequent multiplication and addition
stay well below UINT_MAX. The now-redundant ngroups check and
pr_err in ksmbd_alloc_user() are removed.

This is the response-side analogue of aab98e2dbd64 ("ksmbd: fix
integer overflows on 32 bit systems"), which hardened the request
side.

Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers")
Fixes: a77e0e02af1c ("ksmbd: add support for supplementary groups")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/mgmt/user_config.c | 6 ------
fs/smb/server/transport_ipc.c | 16 +++++++++++++---
2 files changed, 13 insertions(+), 9 deletions(-)

--- a/fs/smb/server/mgmt/user_config.c
+++ b/fs/smb/server/mgmt/user_config.c
@@ -56,12 +56,6 @@ struct ksmbd_user *ksmbd_alloc_user(stru
goto err_free;

if (resp_ext) {
- if (resp_ext->ngroups > NGROUPS_MAX) {
- pr_err("ngroups(%u) from login response exceeds max groups(%d)\n",
- resp_ext->ngroups, NGROUPS_MAX);
- goto err_free;
- }
-
user->sgid = kmemdup(resp_ext->____payload,
resp_ext->ngroups * sizeof(gid_t),
KSMBD_DEFAULT_GFP);
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -13,6 +13,7 @@
#include <net/genetlink.h>
#include <linux/socket.h>
#include <linux/workqueue.h>
+#include <linux/overflow.h>

#include "vfs_cache.h"
#include "transport_ipc.h"
@@ -497,7 +498,9 @@ static int ipc_validate_msg(struct ipc_m
{
struct ksmbd_rpc_command *resp = entry->response;

- msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz;
+ if (check_add_overflow(sizeof(struct ksmbd_rpc_command),
+ resp->payload_sz, &msg_sz))
+ return -EINVAL;
break;
}
case KSMBD_EVENT_SPNEGO_AUTHEN_REQUEST:
@@ -516,8 +519,9 @@ static int ipc_validate_msg(struct ipc_m
if (resp->payload_sz < resp->veto_list_sz)
return -EINVAL;

- msg_sz = sizeof(struct ksmbd_share_config_response) +
- resp->payload_sz;
+ if (check_add_overflow(sizeof(struct ksmbd_share_config_response),
+ resp->payload_sz, &msg_sz))
+ return -EINVAL;
}
break;
}
@@ -526,6 +530,12 @@ static int ipc_validate_msg(struct ipc_m
struct ksmbd_login_response_ext *resp = entry->response;

if (resp->ngroups) {
+ if (resp->ngroups < 0 ||
+ resp->ngroups > NGROUPS_MAX) {
+ pr_err("ngroups(%d) from login response exceeds max groups(%d)\n",
+ resp->ngroups, NGROUPS_MAX);
+ return -EINVAL;
+ }
msg_sz = sizeof(struct ksmbd_login_response_ext) +
resp->ngroups * sizeof(gid_t);
}