ksmbd: fix integer overflows on 32 bit systems

[PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

Posted by Dan Carpenter 11 months, 2 weeks ago

On 32bit systems the addition operations in ipc_msg_alloc() can
potentially overflow leading to memory corruption.  Fix this using
size_add() which will ensure that the invalid allocations do not succeed.
In the callers, move the two constant values
"sizeof(struct ksmbd_rpc_command) + 1" onto the same side and use
size_add() for the user controlled values.

Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
I sent this patch in Oct 2023 but it wasn't applied.
https://lore.kernel.org/all/205c4ec1-7c41-4f5d-8058-501fc1b5163c@moroto.mountain/
I reviewed this code again today and it is still an issue.

 fs/smb/server/transport_ipc.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index befaf42b84cc..ec72c97b2f0b 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -242,7 +242,7 @@ static void ipc_update_last_active(void)
 static struct ksmbd_ipc_msg *ipc_msg_alloc(size_t sz)
 {
 	struct ksmbd_ipc_msg *msg;
-	size_t msg_sz = sz + sizeof(struct ksmbd_ipc_msg);
+	size_t msg_sz = size_add(sz, sizeof(struct ksmbd_ipc_msg));
 
 	msg = kvzalloc(msg_sz, KSMBD_DEFAULT_GFP);
 	if (msg)
@@ -626,8 +626,8 @@ ksmbd_ipc_spnego_authen_request(const char *spnego_blob, int blob_len)
 	struct ksmbd_spnego_authen_request *req;
 	struct ksmbd_spnego_authen_response *resp;
 
-	msg = ipc_msg_alloc(sizeof(struct ksmbd_spnego_authen_request) +
-			blob_len + 1);
+	msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_spnego_authen_request) + 1,
+				     blob_len));
 	if (!msg)
 		return NULL;
 
@@ -805,7 +805,8 @@ struct ksmbd_rpc_command *ksmbd_rpc_write(struct ksmbd_session *sess, int handle
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
-	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
+	msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1,
+				     payload_sz));
 	if (!msg)
 		return NULL;
 
@@ -853,7 +854,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioctl(struct ksmbd_session *sess, int handle
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
-	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
+	msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1, payload_sz));
 	if (!msg)
 		return NULL;
 
@@ -878,7 +879,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_rap(struct ksmbd_session *sess, void *payloa
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
-	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
+	msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1, payload_sz));
 	if (!msg)
 		return NULL;
 
-- 
2.45.2

Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

Posted by Namjae Jeon 11 months, 1 week ago

On Mon, Jan 13, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
>
> On 32bit systems the addition operations in ipc_msg_alloc() can
> potentially overflow leading to memory corruption.  Fix this using
> size_add() which will ensure that the invalid allocations do not succeed.
You previously said that memcpy overrun does not occur due to memory
allocation failure with SIZE_MAX.
Would it be better to handle integer overflows as an error before
memory allocation?
And static checkers don't detect memcpy overrun by considering memory
allocation failure?

Thanks.
> In the callers, move the two constant values
> "sizeof(struct ksmbd_rpc_command) + 1" onto the same side and use
> size_add() for the user controlled values.
>
> Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
> I sent this patch in Oct 2023 but it wasn't applied.
> https://lore.kernel.org/all/205c4ec1-7c41-4f5d-8058-501fc1b5163c@moroto.mountain/
> I reviewed this code again today and it is still an issue.
>
>  fs/smb/server/transport_ipc.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
> index befaf42b84cc..ec72c97b2f0b 100644
> --- a/fs/smb/server/transport_ipc.c
> +++ b/fs/smb/server/transport_ipc.c
> @@ -242,7 +242,7 @@ static void ipc_update_last_active(void)
>  static struct ksmbd_ipc_msg *ipc_msg_alloc(size_t sz)
>  {
>         struct ksmbd_ipc_msg *msg;
> -       size_t msg_sz = sz + sizeof(struct ksmbd_ipc_msg);
> +       size_t msg_sz = size_add(sz, sizeof(struct ksmbd_ipc_msg));
>
>         msg = kvzalloc(msg_sz, KSMBD_DEFAULT_GFP);
>         if (msg)
> @@ -626,8 +626,8 @@ ksmbd_ipc_spnego_authen_request(const char *spnego_blob, int blob_len)
>         struct ksmbd_spnego_authen_request *req;
>         struct ksmbd_spnego_authen_response *resp;
>
> -       msg = ipc_msg_alloc(sizeof(struct ksmbd_spnego_authen_request) +
> -                       blob_len + 1);
> +       msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_spnego_authen_request) + 1,
> +                                    blob_len));
>         if (!msg)
>                 return NULL;
>
> @@ -805,7 +805,8 @@ struct ksmbd_rpc_command *ksmbd_rpc_write(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> -       msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
> +       msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1,
> +                                    payload_sz));
>         if (!msg)
>                 return NULL;
>
> @@ -853,7 +854,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioctl(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> -       msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
> +       msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1, payload_sz));
>         if (!msg)
>                 return NULL;
>
> @@ -878,7 +879,7 @@ struct ksmbd_rpc_command *ksmbd_rpc_rap(struct ksmbd_session *sess, void *payloa
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> -       msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
> +       msg = ipc_msg_alloc(size_add(sizeof(struct ksmbd_rpc_command) + 1, payload_sz));
>         if (!msg)
>                 return NULL;
>
> --
> 2.45.2
>

Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

Posted by Dan Carpenter 11 months, 1 week ago

On Tue, Jan 14, 2025 at 04:53:18PM +0900, Namjae Jeon wrote:
> On Mon, Jan 13, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >
> > On 32bit systems the addition operations in ipc_msg_alloc() can
> > potentially overflow leading to memory corruption.  Fix this using
> > size_add() which will ensure that the invalid allocations do not succeed.
> You previously said that memcpy overrun does not occur due to memory
> allocation failure with SIZE_MAX.
>
> Would it be better to handle integer overflows as an error before
> memory allocation?

I mean we could do something like the below patch but I'd prefer to fix
it this way.

> And static checkers don't detect memcpy overrun by considering memory
> allocation failure?

How the struct_size()/array_size() kernel hardenning works is that if
you pass in a too large value instead of wrapping to a small value, the
math results in SIZE_MAX so the allocation will fail.  We already handle
allocation failures correctly so it's fine.

The problem in this code is that on 32 bit systems if you chose a "sz"
value which is (unsigned int)-4 then the kvzalloc() allocation will
succeed but the buffer will be 4 bytes smaller than intended and the
"msg->sz = sz;" assignment will corrupt memory.

Anyway, here is how the patch could look like with bounds checking instead
of size_add().  We could fancy it up a bit, but I don't like fancy math.

regards,
dan carpenter

diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
index befaf42b84cc..e1e3bfff163c 100644
--- a/fs/smb/server/transport_ipc.c
+++ b/fs/smb/server/transport_ipc.c
@@ -626,6 +626,9 @@ ksmbd_ipc_spnego_authen_request(const char *spnego_blob, int blob_len)
 	struct ksmbd_spnego_authen_request *req;
 	struct ksmbd_spnego_authen_response *resp;
 
+	if (blob_len > INT_MAX)
+		return NULL;
+
 	msg = ipc_msg_alloc(sizeof(struct ksmbd_spnego_authen_request) +
 			blob_len + 1);
 	if (!msg)
@@ -805,6 +808,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_write(struct ksmbd_session *sess, int handle
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
+	if (payload_sz > INT_MAX)
+		return NULL;
+
 	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
 	if (!msg)
 		return NULL;
@@ -853,6 +859,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioctl(struct ksmbd_session *sess, int handle
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
+	if (payload_sz > INT_MAX)
+		return NULL;
+
 	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
 	if (!msg)
 		return NULL;
@@ -878,6 +887,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_rap(struct ksmbd_session *sess, void *payloa
 	struct ksmbd_rpc_command *req;
 	struct ksmbd_rpc_command *resp;
 
+	if (payload_sz > INT_MAX)
+		return NULL;
+
 	msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
 	if (!msg)
 		return NULL;

Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

Posted by Namjae Jeon 11 months, 1 week ago

On Tue, Jan 14, 2025 at 7:18 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
>
> On Tue, Jan 14, 2025 at 04:53:18PM +0900, Namjae Jeon wrote:
> > On Mon, Jan 13, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> > >
> > > On 32bit systems the addition operations in ipc_msg_alloc() can
> > > potentially overflow leading to memory corruption.  Fix this using
> > > size_add() which will ensure that the invalid allocations do not succeed.
> > You previously said that memcpy overrun does not occur due to memory
> > allocation failure with SIZE_MAX.
> >
> > Would it be better to handle integer overflows as an error before
> > memory allocation?
>
> I mean we could do something like the below patch but I'd prefer to fix
> it this way.
>
> > And static checkers don't detect memcpy overrun by considering memory
> > allocation failure?
>
> How the struct_size()/array_size() kernel hardenning works is that if
> you pass in a too large value instead of wrapping to a small value, the
> math results in SIZE_MAX so the allocation will fail.  We already handle
> allocation failures correctly so it's fine.
>
> The problem in this code is that on 32 bit systems if you chose a "sz"
> value which is (unsigned int)-4 then the kvzalloc() allocation will
> succeed but the buffer will be 4 bytes smaller than intended and the
> "msg->sz = sz;" assignment will corrupt memory.
>
> Anyway, here is how the patch could look like with bounds checking instead
> of size_add().  We could fancy it up a bit, but I don't like fancy math.
Okay, There was a macro for max ipc payload size, So I have changed
INT_MAX to KSMBD_IPC_MAX_PAYLOAD.
I will apply it to #ksmbd-for-next-next.
Thanks!
>
> regards,
> dan carpenter
>
> diff --git a/fs/smb/server/transport_ipc.c b/fs/smb/server/transport_ipc.c
> index befaf42b84cc..e1e3bfff163c 100644
> --- a/fs/smb/server/transport_ipc.c
> +++ b/fs/smb/server/transport_ipc.c
> @@ -626,6 +626,9 @@ ksmbd_ipc_spnego_authen_request(const char *spnego_blob, int blob_len)
>         struct ksmbd_spnego_authen_request *req;
>         struct ksmbd_spnego_authen_response *resp;
>
> +       if (blob_len > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_spnego_authen_request) +
>                         blob_len + 1);
>         if (!msg)
> @@ -805,6 +808,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_write(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;
> @@ -853,6 +859,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_ioctl(struct ksmbd_session *sess, int handle
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;
> @@ -878,6 +887,9 @@ struct ksmbd_rpc_command *ksmbd_rpc_rap(struct ksmbd_session *sess, void *payloa
>         struct ksmbd_rpc_command *req;
>         struct ksmbd_rpc_command *resp;
>
> +       if (payload_sz > INT_MAX)
> +               return NULL;
> +
>         msg = ipc_msg_alloc(sizeof(struct ksmbd_rpc_command) + payload_sz + 1);
>         if (!msg)
>                 return NULL;

Re: [PATCH RESEND] ksmbd: fix integer overflows on 32 bit systems

Posted by Dan Carpenter 11 months, 1 week ago

On Wed, Jan 15, 2025 at 09:20:54AM +0900, Namjae Jeon wrote:
> On Tue, Jan 14, 2025 at 7:18 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >
> > On Tue, Jan 14, 2025 at 04:53:18PM +0900, Namjae Jeon wrote:
> > > On Mon, Jan 13, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> > > >
> > > > On 32bit systems the addition operations in ipc_msg_alloc() can
> > > > potentially overflow leading to memory corruption.  Fix this using
> > > > size_add() which will ensure that the invalid allocations do not succeed.
> > > You previously said that memcpy overrun does not occur due to memory
> > > allocation failure with SIZE_MAX.
> > >
> > > Would it be better to handle integer overflows as an error before
> > > memory allocation?
> >
> > I mean we could do something like the below patch but I'd prefer to fix
> > it this way.
> >
> > > And static checkers don't detect memcpy overrun by considering memory
> > > allocation failure?
> >
> > How the struct_size()/array_size() kernel hardenning works is that if
> > you pass in a too large value instead of wrapping to a small value, the
> > math results in SIZE_MAX so the allocation will fail.  We already handle
> > allocation failures correctly so it's fine.
> >
> > The problem in this code is that on 32 bit systems if you chose a "sz"
> > value which is (unsigned int)-4 then the kvzalloc() allocation will
> > succeed but the buffer will be 4 bytes smaller than intended and the
> > "msg->sz = sz;" assignment will corrupt memory.
> >
> > Anyway, here is how the patch could look like with bounds checking instead
> > of size_add().  We could fancy it up a bit, but I don't like fancy math.
> Okay, There was a macro for max ipc payload size, So I have changed
> INT_MAX to KSMBD_IPC_MAX_PAYLOAD.

Nice.  I didn't know.  Thanks!

regards,
dan carpenter