[PATCH v2] batman-adv: Add flex array to struct batadv_tvlv_tt_data
From: Erick Archer
Date: Fri Apr 26 2024 - 13:28:43 EST
The "struct batadv_tvlv_tt_data" uses a dynamically sized set of
trailing elements. Specifically, it uses an array of structures of type
"batadv_tvlv_tt_vlan_data". So, use the preferred way in the kernel
declaring a flexible array [1].
At the same time, prepare for the coming implementation by GCC and Clang
of the __counted_by attribute. Flexible array members annotated with
__counted_by can have their accesses bounds-checked at run-time via
CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE (for
strcpy/memcpy-family functions). In this case, it is important to note
that the attribute used is specifically __counted_by_be since variable
"num_vlan" is of type __be16.
The order in which the structure batadv_tvlv_tt_data and the structure
batadv_tvlv_tt_vlan_data are defined must be swap to avoid an incomplete
type error.
Also, avoid the open-coded arithmetic in memory allocator functions [2]
using the "struct_size" macro and use the "flex_array_size" helper to
clarify some calculations, when possible.
Moreover, the new structure member also allow us to avoid the open-coded
arithmetic on pointers in some situations. Take advantage of this.
This code was detected with the help of Coccinelle, and audited and
modified manually.
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#zero-length-and-one-element-arrays [1]
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [2]
Signed-off-by: Erick Archer <erick.archer@xxxxxxxxxxx>
---
Changes in v2:
- Add the #include of <linux/overflow.h> for the "flex_array_size"
helper (Sven Eckelmann).
- Add the "ntohs" function to the "flex_array_size" helper removed
by mistake during the conversion (Sven Eckelmann).
- Add the "__counted_by_be" attribute.
Previous versions:
v1 -> https://lore.kernel.org/linux-hardening/AS8PR02MB7237987BF9DFCA030B330F658B3E2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Hi,
In this version I have worked on the "sparse" warnings. The difference
in "sparse" warnings before and after this patch is as follows:
net/batman-adv/translation-table.c:534:21: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:819:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:819:25: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:819:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:819:25: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:819:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:898:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:898:25: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:898:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:898:25: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:898:25: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:2892:16: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:2892:16: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:2892:16: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:2892:16: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:2892:16: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:3338:21: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:3338:21: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3338:21: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:3338:21: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3338:21: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:3942:30: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3946:27: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3950:21: warning: expression using sizeof(void)
net/batman-adv/translation-table.c:3986:30: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3990:27: warning: using sizeof on a flexible structure
net/batman-adv/translation-table.c:3992:23: warning: expression using sizeof(void)
As far as I know, these warnings cannot be removed. However it can be
safely ignored since:
Case 1: Warning "using sizeof on a flexible structure"
The commit 1a88f2f24619 ("flex-array: warn when using sizeof() on a flexible array")
in the sparse git repository says
Using sizeof() on a structure containing a flexible array
will ignore the 'flexible' part. This is maybe what is expected
but maybe not, so add an option -Wflexible-array-sizeof to
warn on such usage.
In this patch we take care of using or ignoring the flexible part
when necessary. Therefore, these warnings can be safely ignored.
Case 2: Warning "expression using sizeof(void)"
This warning is implied by the use of the "struct_size" helper and
"flex_array_size" helper because they both use the "__is_constexpr"
macro. And this macro is defined using "sizeof(void)".
/*
* This returns a constant expression while determining if an argument is
* a constant expression, most importantly without evaluating the argument.
* Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx>
*
* Details:
* - sizeof() return an integer constant expression, and does not evaluate
* the value of its operand; it only examines the type of its operand.
* - The results of comparing two integer constant expressions is also
* an integer constant expression.
* - The first literal "8" isn't important. It could be any literal value.
* - The second literal "8" is to avoid warnings about unaligned pointers;
* this could otherwise just be "1".
* - (long)(x) is used to avoid warnings about 64-bit types on 32-bit
* architectures.
* - The C Standard defines "null pointer constant", "(void *)0", as
* distinct from other void pointers.
* - If (x) is an integer constant expression, then the "* 0l" resolves
* it into an integer constant expression of value 0. Since it is cast to
* "void *", this makes the second operand a null pointer constant.
* - If (x) is not an integer constant expression, then the second operand
* resolves to a void pointer (but not a null pointer constant: the value
* is not an integer constant 0).
* - The conditional operator's third operand, "(int *)8", is an object
* pointer (to type "int").
* - The behavior (including the return type) of the conditional operator
* ("operand1 ? operand2 : operand3") depends on the kind of expressions
* given for the second and third operands. This is the central mechanism
* of the macro:
* - When one operand is a null pointer constant (i.e. when x is an integer
* constant expression) and the other is an object pointer (i.e. our
* third operand), the conditional operator returns the type of the
* object pointer operand (i.e. "int *"). Here, within the sizeof(), we
* would then get:
* sizeof(*((int *)(...)) == sizeof(int) == 4
* - When one operand is a void pointer (i.e. when x is not an integer
* constant expression) and the other is an object pointer (i.e. our
* third operand), the conditional operator returns a "void *" type.
* Here, within the sizeof(), we would then get:
* sizeof(*((void *)(...)) == sizeof(void) == 1
* - The equality comparison to "sizeof(int)" therefore depends on (x):
* sizeof(int) == sizeof(int) (x) was a constant expression
* sizeof(int) != sizeof(void) (x) was not a constant expression
*/
#define __is_constexpr(x) \
(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
Therefore, these warnings can also be safely ignored.
The Coccinelle script used to detect this code pattern is the following:
virtual report
@rule1@
type t1;
type t2;
identifier i0;
identifier i1;
identifier i2;
identifier ALLOC =~ "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
position p1;
@@
i0 = sizeof(t1) + sizeof(t2) * i1;
..
i2 = ALLOC@p1(..., i0, ...);
@script:python depends on report@
p1 << rule1.p1;
@@
msg = "WARNING: verify allocation on line %s" % (p1[0].line)
coccilib.report.print_report(p1[0],msg)
Regards,
Erick
---
include/uapi/linux/batadv_packet.h | 28 +++++++++--------
net/batman-adv/translation-table.c | 49 ++++++++++++------------------
2 files changed, 35 insertions(+), 42 deletions(-)
diff --git a/include/uapi/linux/batadv_packet.h b/include/uapi/linux/batadv_packet.h
index 6e25753015df..dfbe30536995 100644
--- a/include/uapi/linux/batadv_packet.h
+++ b/include/uapi/linux/batadv_packet.h
@@ -592,19 +592,6 @@ struct batadv_tvlv_gateway_data {
__be32 bandwidth_up;
};
-/**
- * struct batadv_tvlv_tt_data - tt data propagated through the tt tvlv container
- * @flags: translation table flags (see batadv_tt_data_flags)
- * @ttvn: translation table version number
- * @num_vlan: number of announced VLANs. In the TVLV this struct is followed by
- * one batadv_tvlv_tt_vlan_data object per announced vlan
- */
-struct batadv_tvlv_tt_data {
- __u8 flags;
- __u8 ttvn;
- __be16 num_vlan;
-};
-
/**
* struct batadv_tvlv_tt_vlan_data - vlan specific tt data propagated through
* the tt tvlv container
@@ -618,6 +605,21 @@ struct batadv_tvlv_tt_vlan_data {
__u16 reserved;
};
+/**
+ * struct batadv_tvlv_tt_data - tt data propagated through the tt tvlv container
+ * @flags: translation table flags (see batadv_tt_data_flags)
+ * @ttvn: translation table version number
+ * @num_vlan: number of announced VLANs. In the TVLV this struct is followed by
+ * one batadv_tvlv_tt_vlan_data object per announced vlan
+ * @vlan_data: array of batadv_tvlv_tt_vlan_data objects
+ */
+struct batadv_tvlv_tt_data {
+ __u8 flags;
+ __u8 ttvn;
+ __be16 num_vlan;
+ struct batadv_tvlv_tt_vlan_data vlan_data[] __counted_by_be(num_vlan);
+};
+
/**
* struct batadv_tvlv_tt_change - translation table diff data
* @flags: status indicators concerning the non-mesh client (see
diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
index b21ff3c36b07..d66fd900181c 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -28,6 +28,7 @@
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/netlink.h>
+#include <linux/overflow.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/skbuff.h>
@@ -815,8 +816,7 @@ batadv_tt_prepare_tvlv_global_data(struct batadv_orig_node *orig_node,
num_entries += atomic_read(&vlan->tt.num_entries);
}
- change_offset = sizeof(**tt_data);
- change_offset += num_vlan * sizeof(*tt_vlan);
+ change_offset = struct_size(*tt_data, vlan_data, num_vlan);
/* if tt_len is negative, allocate the space needed by the full table */
if (*tt_len < 0)
@@ -835,7 +835,7 @@ batadv_tt_prepare_tvlv_global_data(struct batadv_orig_node *orig_node,
(*tt_data)->ttvn = atomic_read(&orig_node->last_ttvn);
(*tt_data)->num_vlan = htons(num_vlan);
- tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(*tt_data + 1);
+ tt_vlan = (*tt_data)->vlan_data;
hlist_for_each_entry(vlan, &orig_node->vlan_list, list) {
tt_vlan->vid = htons(vlan->vid);
tt_vlan->crc = htonl(vlan->tt.crc);
@@ -895,8 +895,7 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv,
total_entries += vlan_entries;
}
- change_offset = sizeof(**tt_data);
- change_offset += num_vlan * sizeof(*tt_vlan);
+ change_offset = struct_size(*tt_data, vlan_data, num_vlan);
/* if tt_len is negative, allocate the space needed by the full table */
if (*tt_len < 0)
@@ -915,7 +914,7 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv,
(*tt_data)->ttvn = atomic_read(&bat_priv->tt.vn);
(*tt_data)->num_vlan = htons(num_vlan);
- tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(*tt_data + 1);
+ tt_vlan = (*tt_data)->vlan_data;
hlist_for_each_entry(vlan, &bat_priv->softif_vlan_list, list) {
vlan_entries = atomic_read(&vlan->tt.num_entries);
if (vlan_entries < 1)
@@ -2875,7 +2874,6 @@ static bool batadv_send_tt_request(struct batadv_priv *bat_priv,
{
struct batadv_tvlv_tt_data *tvlv_tt_data = NULL;
struct batadv_tt_req_node *tt_req_node = NULL;
- struct batadv_tvlv_tt_vlan_data *tt_vlan_req;
struct batadv_hard_iface *primary_if;
bool ret = false;
int i, size;
@@ -2891,7 +2889,7 @@ static bool batadv_send_tt_request(struct batadv_priv *bat_priv,
if (!tt_req_node)
goto out;
- size = sizeof(*tvlv_tt_data) + sizeof(*tt_vlan_req) * num_vlan;
+ size = struct_size(tvlv_tt_data, vlan_data, num_vlan);
tvlv_tt_data = kzalloc(size, GFP_ATOMIC);
if (!tvlv_tt_data)
goto out;
@@ -2903,12 +2901,10 @@ static bool batadv_send_tt_request(struct batadv_priv *bat_priv,
/* send all the CRCs within the request. This is needed by intermediate
* nodes to ensure they have the correct table before replying
*/
- tt_vlan_req = (struct batadv_tvlv_tt_vlan_data *)(tvlv_tt_data + 1);
for (i = 0; i < num_vlan; i++) {
- tt_vlan_req->vid = tt_vlan->vid;
- tt_vlan_req->crc = tt_vlan->crc;
+ tvlv_tt_data->vlan_data[i].vid = tt_vlan->vid;
+ tvlv_tt_data->vlan_data[i].crc = tt_vlan->crc;
- tt_vlan_req++;
tt_vlan++;
}
@@ -2960,7 +2956,6 @@ static bool batadv_send_other_tt_response(struct batadv_priv *bat_priv,
struct batadv_orig_node *res_dst_orig_node = NULL;
struct batadv_tvlv_tt_change *tt_change;
struct batadv_tvlv_tt_data *tvlv_tt_data = NULL;
- struct batadv_tvlv_tt_vlan_data *tt_vlan;
bool ret = false, full_table;
u8 orig_ttvn, req_ttvn;
u16 tvlv_len;
@@ -2983,10 +2978,9 @@ static bool batadv_send_other_tt_response(struct batadv_priv *bat_priv,
orig_ttvn = (u8)atomic_read(&req_dst_orig_node->last_ttvn);
req_ttvn = tt_data->ttvn;
- tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(tt_data + 1);
/* this node doesn't have the requested data */
if (orig_ttvn != req_ttvn ||
- !batadv_tt_global_check_crc(req_dst_orig_node, tt_vlan,
+ !batadv_tt_global_check_crc(req_dst_orig_node, tt_data->vlan_data,
ntohs(tt_data->num_vlan)))
goto out;
@@ -3329,7 +3323,6 @@ static void batadv_handle_tt_response(struct batadv_priv *bat_priv,
struct batadv_orig_node *orig_node = NULL;
struct batadv_tvlv_tt_change *tt_change;
u8 *tvlv_ptr = (u8 *)tt_data;
- u16 change_offset;
batadv_dbg(BATADV_DBG_TT, bat_priv,
"Received TT_RESPONSE from %pM for ttvn %d t_size: %d [%c]\n",
@@ -3342,10 +3335,7 @@ static void batadv_handle_tt_response(struct batadv_priv *bat_priv,
spin_lock_bh(&orig_node->tt_lock);
- change_offset = sizeof(struct batadv_tvlv_tt_vlan_data);
- change_offset *= ntohs(tt_data->num_vlan);
- change_offset += sizeof(*tt_data);
- tvlv_ptr += change_offset;
+ tvlv_ptr += struct_size(tt_data, vlan_data, ntohs(tt_data->num_vlan));
tt_change = (struct batadv_tvlv_tt_change *)tvlv_ptr;
if (tt_data->flags & BATADV_TT_FULL_TABLE) {
@@ -3944,10 +3934,10 @@ static void batadv_tt_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
u8 flags, void *tvlv_value,
u16 tvlv_value_len)
{
- struct batadv_tvlv_tt_vlan_data *tt_vlan;
struct batadv_tvlv_tt_change *tt_change;
struct batadv_tvlv_tt_data *tt_data;
u16 num_entries, num_vlan;
+ size_t flex_size;
if (tvlv_value_len < sizeof(*tt_data))
return;
@@ -3957,17 +3947,18 @@ static void batadv_tt_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
num_vlan = ntohs(tt_data->num_vlan);
- if (tvlv_value_len < sizeof(*tt_vlan) * num_vlan)
+ flex_size = flex_array_size(tt_data, vlan_data, num_vlan);
+ if (tvlv_value_len < flex_size)
return;
- tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(tt_data + 1);
- tt_change = (struct batadv_tvlv_tt_change *)(tt_vlan + num_vlan);
- tvlv_value_len -= sizeof(*tt_vlan) * num_vlan;
+ tt_change = (struct batadv_tvlv_tt_change *)(tt_data->vlan_data +
+ num_vlan);
+ tvlv_value_len -= flex_size;
num_entries = batadv_tt_entries(tvlv_value_len);
- batadv_tt_update_orig(bat_priv, orig, tt_vlan, num_vlan, tt_change,
- num_entries, tt_data->ttvn);
+ batadv_tt_update_orig(bat_priv, orig, tt_data->vlan_data, num_vlan,
+ tt_change, num_entries, tt_data->ttvn);
}
/**
@@ -3998,8 +3989,8 @@ static int batadv_tt_tvlv_unicast_handler_v1(struct batadv_priv *bat_priv,
tt_data = tvlv_value;
tvlv_value_len -= sizeof(*tt_data);
- tt_vlan_len = sizeof(struct batadv_tvlv_tt_vlan_data);
- tt_vlan_len *= ntohs(tt_data->num_vlan);
+ tt_vlan_len = flex_array_size(tt_data, vlan_data,
+ ntohs(tt_data->num_vlan));
if (tvlv_value_len < tt_vlan_len)
return NET_RX_SUCCESS;
--
2.25.1