qed/red_ll2: Fix undefined behavior bug in struct qed_ll2_info

The flexible structure (a structure that contains a flexible-array member
at the end) `qed_ll2_tx_packet` is nested within the second layer of
`struct qed_ll2_info`:

struct qed_ll2_tx_packet {
	...
        /* Flexible Array of bds_set determined by max_bds_per_packet */
        struct {
                struct core_tx_bd *txq_bd;
                dma_addr_t tx_frag;
                u16 frag_len;
        } bds_set[];
};

struct qed_ll2_tx_queue {
	...
	struct qed_ll2_tx_packet cur_completing_packet;
};

struct qed_ll2_info {
	...
	struct qed_ll2_tx_queue tx_queue;
        struct qed_ll2_cbs cbs;
};

The problem is that member `cbs` in `struct qed_ll2_info` is placed just
after an object of type `struct qed_ll2_tx_queue`, which is in itself
an implicit flexible structure, which by definition ends in a flexible
array member, in this case `bds_set`. This causes an undefined behavior
bug at run-time when dynamic memory is allocated for `bds_set`, which
could lead to a serious issue if `cbs` in `struct qed_ll2_info` is
overwritten by the contents of `bds_set`. Notice that the type of `cbs`
is a structure full of function pointers (and a cookie :) ):

include/linux/qed/qed_ll2_if.h:
107 typedef
108 void (*qed_ll2_complete_rx_packet_cb)(void *cxt,
109                                       struct qed_ll2_comp_rx_data *data);
110
111 typedef
112 void (*qed_ll2_release_rx_packet_cb)(void *cxt,
113                                      u8 connection_handle,
114                                      void *cookie,
115                                      dma_addr_t rx_buf_addr,
116                                      bool b_last_packet);
117
118 typedef
119 void (*qed_ll2_complete_tx_packet_cb)(void *cxt,
120                                       u8 connection_handle,
121                                       void *cookie,
122                                       dma_addr_t first_frag_addr,
123                                       bool b_last_fragment,
124                                       bool b_last_packet);
125
126 typedef
127 void (*qed_ll2_release_tx_packet_cb)(void *cxt,
128                                      u8 connection_handle,
129                                      void *cookie,
130                                      dma_addr_t first_frag_addr,
131                                      bool b_last_fragment, bool b_last_packet);
132
133 typedef
134 void (*qed_ll2_slowpath_cb)(void *cxt, u8 connection_handle,
135                             u32 opaque_data_0, u32 opaque_data_1);
136
137 struct qed_ll2_cbs {
138         qed_ll2_complete_rx_packet_cb rx_comp_cb;
139         qed_ll2_release_rx_packet_cb rx_release_cb;
140         qed_ll2_complete_tx_packet_cb tx_comp_cb;
141         qed_ll2_release_tx_packet_cb tx_release_cb;
142         qed_ll2_slowpath_cb slowpath_cb;
143         void *cookie;
144 };

Fix this by moving the declaration of `cbs` to the  middle of its
containing structure `qed_ll2_info`, preventing it from being
overwritten by the contents of `bds_set` at run-time.

This bug was introduced in 2017, when `bds_set` was converted to a
one-element array, and started to be used as a Variable Length Object
(VLO) at run-time.

Fixes: f5823fe689 ("qed: Add ll2 option to limit the number of bds per packet")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/ZQ+Nz8DfPg56pIzr@work
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/qlogic/qed/qed_ll2.h

@@ -110,9 +110,9 @@ struct qed_ll2_info {
 	enum core_tx_dest tx_dest;
 	u8 tx_stats_en;
 	bool main_func_queue;
+	struct qed_ll2_cbs cbs;
 	struct qed_ll2_rx_queue rx_queue;
 	struct qed_ll2_tx_queue tx_queue;
-	struct qed_ll2_cbs cbs;
 };
 
 extern const struct qed_ll2_ops qed_ll2_ops_pass;