When a struct containing a flexible array is included in another struct,
and there is a member after the struct-with-flex-array, there is a
possibility of memory overlap. These cases must be audited [1]. See:
struct inner {
...
int flex[];
};
struct outer {
...
struct inner header;
int overlap;
...
};
This is the scenario for all the "struct *_filter" structures that are
included in the following "struct ib_flow_spec_*" structures:
struct ib_flow_spec_eth
struct ib_flow_spec_ib
struct ib_flow_spec_ipv4
struct ib_flow_spec_ipv6
struct ib_flow_spec_tcp_udp
struct ib_flow_spec_tunnel
struct ib_flow_spec_esp
struct ib_flow_spec_gre
struct ib_flow_spec_mpls
The pattern is like the one shown below:
struct *_filter {
...
u8 real_sz[];
};
struct ib_flow_spec_mpls {
...
struct *_filter val;
struct *_filter mask;
};
In this case, the trailing flexible array "real_sz" is never allocated
and is only used to calculate the size of the structures. Here the use
of the "offsetof" helper can be changed by the "sizeof" operator because
the goal is to get the size of these structures. Therefore, the trailing
flexible arrays can also be removed.
Link: https://github.com/KSPP/linux/issues/202 [1]
Signed-off-by: Erick Archer <[email protected]>
---
Hi everyone,
This patch has not been tested. This has only been built-tested.
Regards,
Erick
---
drivers/infiniband/core/uverbs_cmd.c | 16 ++++++++--------
include/rdma/ib_verbs.h | 17 -----------------
2 files changed, 8 insertions(+), 25 deletions(-)
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 6de05ade2ba9..3d3ee3eca983 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -2737,7 +2737,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
switch (ib_spec->type & ~IB_FLOW_SPEC_INNER) {
case IB_FLOW_SPEC_ETH:
- ib_filter_sz = offsetof(struct ib_flow_eth_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_eth_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2748,7 +2748,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
memcpy(&ib_spec->eth.mask, kern_spec_mask, actual_filter_sz);
break;
case IB_FLOW_SPEC_IPV4:
- ib_filter_sz = offsetof(struct ib_flow_ipv4_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_ipv4_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2759,7 +2759,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
memcpy(&ib_spec->ipv4.mask, kern_spec_mask, actual_filter_sz);
break;
case IB_FLOW_SPEC_IPV6:
- ib_filter_sz = offsetof(struct ib_flow_ipv6_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_ipv6_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2775,7 +2775,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
break;
case IB_FLOW_SPEC_TCP:
case IB_FLOW_SPEC_UDP:
- ib_filter_sz = offsetof(struct ib_flow_tcp_udp_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_tcp_udp_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2786,7 +2786,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
memcpy(&ib_spec->tcp_udp.mask, kern_spec_mask, actual_filter_sz);
break;
case IB_FLOW_SPEC_VXLAN_TUNNEL:
- ib_filter_sz = offsetof(struct ib_flow_tunnel_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_tunnel_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2801,7 +2801,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
return -EINVAL;
break;
case IB_FLOW_SPEC_ESP:
- ib_filter_sz = offsetof(struct ib_flow_esp_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_esp_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2812,7 +2812,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
memcpy(&ib_spec->esp.mask, kern_spec_mask, actual_filter_sz);
break;
case IB_FLOW_SPEC_GRE:
- ib_filter_sz = offsetof(struct ib_flow_gre_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_gre_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
@@ -2823,7 +2823,7 @@ int ib_uverbs_kern_spec_to_ib_spec_filter(enum ib_flow_spec_type type,
memcpy(&ib_spec->gre.mask, kern_spec_mask, actual_filter_sz);
break;
case IB_FLOW_SPEC_MPLS:
- ib_filter_sz = offsetof(struct ib_flow_mpls_filter, real_sz);
+ ib_filter_sz = sizeof(struct ib_flow_mpls_filter);
actual_filter_sz = spec_filter_size(kern_spec_mask,
kern_filter_sz,
ib_filter_sz);
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index b7b6b58dd348..80e814a57034 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -1910,8 +1910,6 @@ struct ib_flow_eth_filter {
u8 src_mac[6];
__be16 ether_type;
__be16 vlan_tag;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_eth {
@@ -1924,8 +1922,6 @@ struct ib_flow_spec_eth {
struct ib_flow_ib_filter {
__be16 dlid;
__u8 sl;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_ib {
@@ -1949,8 +1945,6 @@ struct ib_flow_ipv4_filter {
u8 tos;
u8 ttl;
u8 flags;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_ipv4 {
@@ -1967,8 +1961,6 @@ struct ib_flow_ipv6_filter {
u8 next_hdr;
u8 traffic_class;
u8 hop_limit;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_ipv6 {
@@ -1981,8 +1973,6 @@ struct ib_flow_spec_ipv6 {
struct ib_flow_tcp_udp_filter {
__be16 dst_port;
__be16 src_port;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_tcp_udp {
@@ -1994,7 +1984,6 @@ struct ib_flow_spec_tcp_udp {
struct ib_flow_tunnel_filter {
__be32 tunnel_id;
- u8 real_sz[];
};
/* ib_flow_spec_tunnel describes the Vxlan tunnel
@@ -2010,8 +1999,6 @@ struct ib_flow_spec_tunnel {
struct ib_flow_esp_filter {
__be32 spi;
__be32 seq;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_esp {
@@ -2025,8 +2012,6 @@ struct ib_flow_gre_filter {
__be16 c_ks_res0_ver;
__be16 protocol;
__be32 key;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_gre {
@@ -2038,8 +2023,6 @@ struct ib_flow_spec_gre {
struct ib_flow_mpls_filter {
__be32 tag;
- /* Must be last */
- u8 real_sz[];
};
struct ib_flow_spec_mpls {
--
2.25.1
On Sun, Feb 11, 2024 at 12:58:56PM +0100, Erick Archer wrote:
> When a struct containing a flexible array is included in another struct,
> and there is a member after the struct-with-flex-array, there is a
> possibility of memory overlap. These cases must be audited [1]. See:
>
> struct inner {
> ...
> int flex[];
> };
>
> struct outer {
> ...
> struct inner header;
> int overlap;
> ...
> };
>
> This is the scenario for all the "struct *_filter" structures that are
> included in the following "struct ib_flow_spec_*" structures:
>
> struct ib_flow_spec_eth
> struct ib_flow_spec_ib
> struct ib_flow_spec_ipv4
> struct ib_flow_spec_ipv6
> struct ib_flow_spec_tcp_udp
> struct ib_flow_spec_tunnel
> struct ib_flow_spec_esp
> struct ib_flow_spec_gre
> struct ib_flow_spec_mpls
>
> The pattern is like the one shown below:
>
> struct *_filter {
> ...
> u8 real_sz[];
> };
>
> struct ib_flow_spec_mpls {
> ...
> struct *_filter val;
> struct *_filter mask;
> };
>
> In this case, the trailing flexible array "real_sz" is never allocated
> and is only used to calculate the size of the structures. Here the use
> of the "offsetof" helper can be changed by the "sizeof" operator because
> the goal is to get the size of these structures. Therefore, the trailing
> flexible arrays can also be removed.
>
> Link: https://github.com/KSPP/linux/issues/202 [1]
> Signed-off-by: Erick Archer <[email protected]>
> ---
> Hi everyone,
>
> This patch has not been tested. This has only been built-tested.
I might suggest doing a binary difference comparison[1], as it's possible
that "real_sz" is being used to try to avoid trailing padding on
structs. I wasn't able to trivially construct an example, so maybe I'm
not understanding its purpose correctly.
If, however, there are cases where offsetof(..., real_sz) !=
sizeof(...), then I would check two alternatives:
struct { } real_sz;
but that may induce padding still, or:
u8 real_sz[0];
which would be a literally zero-sized array, used only for addressing.
Or, these can be left as-is, and the "flex array not at end of struct"
warnings can be disabled for these targets.
-Kees
--
Kees Cook
On Mon, Feb 12, 2024 at 10:30:17AM -0800, Kees Cook wrote:
> I might suggest doing a binary difference comparison[1], as it's possible
> that "real_sz" is being used to try to avoid trailing padding on
> structs. I wasn't able to trivially construct an example, so maybe I'm
> not understanding its purpose correctly.
Hmm.. No need for binary comparison:
+static_assert(offsetof(struct ib_flow_eth_filter, real_sz) == sizeof(struct ib_flow_eth_filter));
+static_assert(offsetof(struct ib_flow_ib_filter, real_sz) == sizeof(struct ib_flow_ib_filter));
+static_assert(offsetof(struct ib_flow_tunnel_filter, real_sz) == sizeof(struct ib_flow_tunnel_filter));
+static_assert(offsetof(struct ib_flow_esp_filter, real_sz) == sizeof(struct ib_flow_esp_filter));
+static_assert(offsetof(struct ib_flow_gre_filter, real_sz) == sizeof(struct ib_flow_gre_filter));
+static_assert(offsetof(struct ib_flow_mpls_filter, real_sz) == sizeof(struct ib_flow_mpls_filter));
But yep, it is doing something:
In file included from ../include/linux/mlx5/device.h:37:
./include/rdma/ib_verbs.h:1931:15: error: static assertion failed due to requirement '__builtin_offsetof(struct ib_flow_ib_filter, real_sz) == sizeof(struct ib_flow_ib_filter)': offsetof(struct ib_flow_ib_filter, real_sz) == sizeof(struct ib_flow_ib_filter)
1931 | static_assert(offsetof(struct ib_flow_ib_filter, real_sz) == sizeof(struct ib_flow_ib_filter));
__packed on that struct would probably be be OK.
Jason