On Tue, Dec 03, 2019 at 11:03:45AM -0500, Laura Abbott wrote:
> The sizes for memcpy in flow_offload_mangle don't match
> the source variables, leading to overflow errors on some
> build configurations:
>
> In function 'memcpy',
> inlined from 'flow_offload_mangle' at net/netfilter/nf_flow_table_offload.c:112:2,
> inlined from 'flow_offload_port_dnat' at net/netfilter/nf_flow_table_offload.c:373:2,
> inlined from 'nf_flow_rule_route_ipv4' at net/netfilter/nf_flow_table_offload.c:424:3:
> ./include/linux/string.h:376:4: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter
> 376 | __read_overflow2();
> | ^~~~~~~~~~~~~~~~~~
> make[2]: *** [scripts/Makefile.build:266: net/netfilter/nf_flow_table_offload.o] Error 1
>
> Fix this by using the corresponding type.
>
> Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
> Seen on a Fedora powerpc little endian build with -O3 but it looks like
> it is correctly catching an error with doing a memcpy outside the source
> variable.
Hi,
It is right but the fix is not. In that call trace:
flow_offload_port_dnat() {
...
u32 mask = ~htonl(0xffff);
__be16 port;
...
flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
(u8 *)&port, (u8 *)&mask);
}
port should have a 32b storage as well, and aligned with the mask.
> ---
> net/netfilter/nf_flow_table_offload.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
> index c54c9a6cc981..526f894d0bdb 100644
> --- a/net/netfilter/nf_flow_table_offload.c
> +++ b/net/netfilter/nf_flow_table_offload.c
> @@ -108,8 +108,8 @@ static void flow_offload_mangle(struct flow_action_entry *entry,
> entry->id = FLOW_ACTION_MANGLE;
> entry->mangle.htype = htype;
> entry->mangle.offset = offset;
> - memcpy(&entry->mangle.mask, mask, sizeof(u32));
> - memcpy(&entry->mangle.val, value, sizeof(u32));
^^^^^ ^^^ which is &port in the call above
> + memcpy(&entry->mangle.mask, mask, sizeof(u8));
> + memcpy(&entry->mangle.val, value, sizeof(u8));
This fix would cause it to copy only the first byte, which is not the
intention.
> }
>
> static inline struct flow_action_entry *
> --
> 2.21.0
>
