In order to help the compiler reason about the destination buffer in
struct fc_nl_event, add a flexible array member for this purpose.
However, since the header is UAPI, it must not change size or layout, so
a union is used.
The allocation size calculations are also corrected (it was potentially
allocating an extra 8 bytes), and the padding is zeroed to avoid leaking
kernel heap memory contents.
Detected at run-time by the recently added memcpy() bounds checking:
memcpy: detected field-spanning write (size 8) of single field "&event->event_data" at drivers/scsi/scsi_transport_fc.c:581 (size 4)
Reported-by: Sachin Sant <[email protected]>
Link: https://lore.kernel.org/linux-next/[email protected]/
Cc: "James E.J. Bottomley" <[email protected]>
Cc: "Martin K. Petersen" <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
drivers/scsi/scsi_transport_fc.c | 8 +++++---
include/uapi/scsi/scsi_netlink_fc.h | 7 +++++--
2 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
index a2524106206d..0d798f11dc34 100644
--- a/drivers/scsi/scsi_transport_fc.c
+++ b/drivers/scsi/scsi_transport_fc.c
@@ -543,7 +543,7 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
struct nlmsghdr *nlh;
struct fc_nl_event *event;
const char *name;
- u32 len;
+ size_t len, padding;
int err;
if (!data_buf || data_len < 4)
@@ -554,7 +554,7 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
goto send_fail;
}
- len = FC_NL_MSGALIGN(sizeof(*event) + data_len);
+ len = FC_NL_MSGALIGN(sizeof(*event) - sizeof(event->event_data) + data_len);
skb = nlmsg_new(len, GFP_KERNEL);
if (!skb) {
@@ -578,7 +578,9 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
event->event_num = event_number;
event->event_code = event_code;
if (data_len)
- memcpy(&event->event_data, data_buf, data_len);
+ memcpy(event->event_data_flex, data_buf, data_len);
+ padding = len - offsetof(typeof(*event), event_data_flex) - data_len;
+ memset(event->event_data_flex + data_len, 0, padding);
nlmsg_multicast(scsi_nl_sock, skb, 0, SCSI_NL_GRP_FC_EVENTS,
GFP_KERNEL);
diff --git a/include/uapi/scsi/scsi_netlink_fc.h b/include/uapi/scsi/scsi_netlink_fc.h
index 7535253f1a96..b46e9cbeb001 100644
--- a/include/uapi/scsi/scsi_netlink_fc.h
+++ b/include/uapi/scsi/scsi_netlink_fc.h
@@ -35,7 +35,7 @@
* FC Transport Broadcast Event Message :
* FC_NL_ASYNC_EVENT
*
- * Note: if Vendor Unique message, &event_data will be start of
+ * Note: if Vendor Unique message, event_data_flex will be start of
* vendor unique payload, and the length of the payload is
* per event_datalen
*
@@ -50,7 +50,10 @@ struct fc_nl_event {
__u16 event_datalen;
__u32 event_num;
__u32 event_code;
- __u32 event_data;
+ union {
+ __u32 event_data;
+ __DECLARE_FLEX_ARRAY(__u8, event_data_flex);
+ };
} __attribute__((aligned(sizeof(__u64))));
--
2.34.1
> On 22-Sep-2022, at 2:21 AM, Kees Cook <[email protected]> wrote:
>
> In order to help the compiler reason about the destination buffer in
> struct fc_nl_event, add a flexible array member for this purpose.
> However, since the header is UAPI, it must not change size or layout, so
> a union is used.
>
> The allocation size calculations are also corrected (it was potentially
> allocating an extra 8 bytes), and the padding is zeroed to avoid leaking
> kernel heap memory contents.
>
> Detected at run-time by the recently added memcpy() bounds checking:
>
> memcpy: detected field-spanning write (size 8) of single field "&event->event_data" at drivers/scsi/scsi_transport_fc.c:581 (size 4)
>
> Reported-by: Sachin Sant <[email protected]>
> Link: https://lore.kernel.org/linux-next/[email protected]/
> Cc: "James E.J. Bottomley" <[email protected]>
> Cc: "Martin K. Petersen" <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
Thanks for the fix. With this patch applied the warning is no longer seen.
Tested-by: Sachin Sant <[email protected]>
> drivers/scsi/scsi_transport_fc.c | 8 +++++---
> include/uapi/scsi/scsi_netlink_fc.h | 7 +++++--
> 2 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
> index a2524106206d..0d798f11dc34 100644
> --- a/drivers/scsi/scsi_transport_fc.c
> +++ b/drivers/scsi/scsi_transport_fc.c
> @@ -543,7 +543,7 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
> struct nlmsghdr *nlh;
> struct fc_nl_event *event;
> const char *name;
> - u32 len;
> + size_t len, padding;
> int err;
>
> if (!data_buf || data_len < 4)
> @@ -554,7 +554,7 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
> goto send_fail;
> }
>
> - len = FC_NL_MSGALIGN(sizeof(*event) + data_len);
> + len = FC_NL_MSGALIGN(sizeof(*event) - sizeof(event->event_data) + data_len);
>
> skb = nlmsg_new(len, GFP_KERNEL);
> if (!skb) {
> @@ -578,7 +578,9 @@ fc_host_post_fc_event(struct Scsi_Host *shost, u32 event_number,
> event->event_num = event_number;
> event->event_code = event_code;
> if (data_len)
> - memcpy(&event->event_data, data_buf, data_len);
> + memcpy(event->event_data_flex, data_buf, data_len);
> + padding = len - offsetof(typeof(*event), event_data_flex) - data_len;
> + memset(event->event_data_flex + data_len, 0, padding);
>
> nlmsg_multicast(scsi_nl_sock, skb, 0, SCSI_NL_GRP_FC_EVENTS,
> GFP_KERNEL);
> diff --git a/include/uapi/scsi/scsi_netlink_fc.h b/include/uapi/scsi/scsi_netlink_fc.h
> index 7535253f1a96..b46e9cbeb001 100644
> --- a/include/uapi/scsi/scsi_netlink_fc.h
> +++ b/include/uapi/scsi/scsi_netlink_fc.h
> @@ -35,7 +35,7 @@
> * FC Transport Broadcast Event Message :
> * FC_NL_ASYNC_EVENT
> *
> - * Note: if Vendor Unique message, &event_data will be start of
> + * Note: if Vendor Unique message, event_data_flex will be start of
> * vendor unique payload, and the length of the payload is
> * per event_datalen
> *
> @@ -50,7 +50,10 @@ struct fc_nl_event {
> __u16 event_datalen;
> __u32 event_num;
> __u32 event_code;
> - __u32 event_data;
> + union {
> + __u32 event_data;
> + __DECLARE_FLEX_ARRAY(__u8, event_data_flex);
> + };
> } __attribute__((aligned(sizeof(__u64))));
>
>
> --
> 2.34.1
>
On 9/21/2022 1:51 PM, Kees Cook wrote:
> In order to help the compiler reason about the destination buffer in
> struct fc_nl_event, add a flexible array member for this purpose.
> However, since the header is UAPI, it must not change size or layout, so
> a union is used.
>
> The allocation size calculations are also corrected (it was potentially
> allocating an extra 8 bytes), and the padding is zeroed to avoid leaking
> kernel heap memory contents.
>
> Detected at run-time by the recently added memcpy() bounds checking:
>
> memcpy: detected field-spanning write (size 8) of single field "&event->event_data" at drivers/scsi/scsi_transport_fc.c:581 (size 4)
>
> Reported-by: Sachin Sant <[email protected]>
> Link: https://lore.kernel.org/linux-next/[email protected]/
> Cc: "James E.J. Bottomley" <[email protected]>
> Cc: "Martin K. Petersen" <[email protected]>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
Kinda crazy way to resolve it, but looks fine.
Reviewed-by: James Smart <[email protected]>
-- james
Kees,
> In order to help the compiler reason about the destination buffer in
> struct fc_nl_event, add a flexible array member for this purpose.
> However, since the header is UAPI, it must not change size or layout,
> so a union is used.
Applied to 6.1/scsi-staging, thanks!
--
Martin K. Petersen Oracle Linux Engineering