Re: [PATCH net] net: qede: initialize extack in qede_flow_spec_to_rule()

[Asbjørn Sloth Tønnesen]

On 10/13/26 10:54 AM, Anirudh Virdi wrote:
> qede_flow_spec_to_rule() declares a netlink_ext_ack on the stack
> without initializing it. qede_parse_flow_attr() and
> qede_flow_spec_validate() only set extack._msg on error paths via
> NL_SET_ERR_MSG_MOD(), so on a successful parse the err_out block
> reads an uninitialized pointer. If that garbage happens to be
> non-NULL, DP_NOTICE("%s", extack._msg) dereferences it inside
> vsnprintf, causing a page fault and kernel panic.
>
> This manifests when configuring ethtool ntuple flow rules (ethtool -U
> flow-type tcp4/udp4) on kernels built with CONFIG_INIT_STACK_NONE=y.
> With CONFIG_INIT_STACK_ALL_ZERO=y the bug is masked because the
> compiler zero-initializes extack, making _msg NULL.
>
> Reproduced on RHEL 9.8 (kernel-5.14.0-687.47.1.el9_8) and mainline
> (v7.3-rc6) with the following reproducer:
>
>    IFACE=ens2f0
>    ip link set $IFACE up
>    ethtool -K $IFACE ntuple on
>    for i in $(seq 1 100); do
>      ethtool -U $IFACE flow-type udp4 src-ip 192.168.2.$i action -1
>    done
>
> The loop panics reliably after 10-15 iterations with:
>
>    BUG: unable to handle page fault
>    RIP: string+0x49/0xd0
>    Call Trace:
>     vsnprintf
>     qede_flow_spec_to_rule+0x2b6/0x4b0 [qede]
>     qede_add_cls_rule
>     ethtool_set_rxnfc
>
> Zero-initialize extack so _msg is NULL unless explicitly set by an
> error path.
>
> Fixes: eb705d734525 ("net: qede: use faked extack in qede_flow_spec_to_rule()")
> Signed-off-by: Anirudh Virdi <avirdi@xxxxxxxxxx>

LGTM, thanks.

Reviewed-by: Asbjørn Sloth Tønnesen <ast@xxxxxxxxxxx>

CC Vadim and Ido:
As stated in the blamed commit message, my implementation was based on
mlxsw_env_linecard_modules_power_mode_apply() by commit 06a0fc43bb10
("mlxsw: core_env: Add interfaces for line card initialization and
de-initialization"), so likely that also needs to be fixed. I don't
have the hardware to prove/test that it can be triggered.