dm: replace zero-length array with flexible-array

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 91787cde369bf387a479bf7a3091fbe5bc3fc883..71c651465bddfd4a1335b21febcd15ec07e5b85e 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -214,7 +214,7 @@ struct crypt_config {
        struct mutex bio_alloc_lock;
 
        u8 *authenc_key; /* space for keys in authenc() format (if used) */
-       u8 key[0];
+       u8 key[];
 };
 
 #define MIN_IOS                64

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index 3726b987151e5e6b9a4558ae880de106c3138bdb..f794dca22032e8bcf285fc4c6eb40098894c2372 100644 (file)
--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -92,7 +92,7 @@ struct journal_entry {
                } s;
                __u64 sector;
        } u;
-       commit_id_t last_bytes[0];
+       commit_id_t last_bytes[];
        /* __u8 tag[0]; */
 };
 

diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index 8ea20b56b4d63283aa1c23a82f6d0bc454c75ea3..e3d35c6c9f714d49d6187fbdc2eac1a9df40e29a 100644 (file)
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -127,7 +127,7 @@ struct pending_block {
        char *data;
        u32 datalen;
        struct list_head list;
-       struct bio_vec vecs[0];
+       struct bio_vec vecs[];
 };
 
 struct per_bio_data {

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 9a18bef0a5ff009d06bd512a49e63aec0f0de270..10e8b2fe787b56bd8ceb3662d6879d8c99f64fbf 100644 (file)
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -254,7 +254,7 @@ struct raid_set {
                int mode;
        } journal_dev;
 
-       struct raid_dev dev[0];
+       struct raid_dev dev[];
 };
 
 static void rs_config_backup(struct raid_set *rs, struct rs_layout *l)

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 089aed57e0836342a461c6cb12d9e54207797009..2f655d9f42006416a47f019aec1eeeaefc1c97c1 100644 (file)
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -83,7 +83,7 @@ struct mirror_set {
        struct work_struct trigger_event;
 
        unsigned nr_mirrors;
-       struct mirror mirror[0];
+       struct mirror mirror[];
 };
 
 DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,

diff --git a/drivers/md/dm-stats.c b/drivers/md/dm-stats.c
index 71417048256af1d3be307b9d6938aa0f6e07ee4b..35d368c418d0301df2de8c6c7762950dc0fe446d 100644 (file)
--- a/drivers/md/dm-stats.c
+++ b/drivers/md/dm-stats.c
@@ -56,7 +56,7 @@ struct dm_stat {
        size_t percpu_alloc_size;
        size_t histogram_alloc_size;
        struct dm_stat_percpu *stat_percpu[NR_CPUS];
-       struct dm_stat_shared stat_shared[0];
+       struct dm_stat_shared stat_shared[];
 };
 
 #define STAT_PRECISE_TIMESTAMPS                1

diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index fa813c0f993d0d373693b284bb59f7fef7615011..151d022b032d4096e0df7353dfe8fa5ce04d2b21 100644 (file)
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -41,7 +41,7 @@ struct stripe_c {
        /* Work struct used for triggering events*/
        struct work_struct trigger_event;
 
-       struct stripe stripe[0];
+       struct stripe stripe[];
 };
 
 /*

diff --git a/drivers/md/dm-switch.c b/drivers/md/dm-switch.c
index 8a0f057b81220288afd70404ab83d8a5c10cefcf..bff4c7fa1cd2181f2f2244e919623751dcda553e 100644 (file)
--- a/drivers/md/dm-switch.c
+++ b/drivers/md/dm-switch.c
@@ -53,7 +53,7 @@ struct switch_ctx {
        /*
         * Array of dm devices to switch between.
         */
-       struct switch_path path_list[0];
+       struct switch_path path_list[];
 };
 
 static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_paths,

diff --git a/drivers/md/persistent-data/dm-btree-internal.h b/drivers/md/persistent-data/dm-btree-internal.h
index 55a4096f1334f11cad9e394a979b41ee5d57370b..564896659dd44609e679162aff1e948a0e00d4d0 100644 (file)
--- a/drivers/md/persistent-data/dm-btree-internal.h
+++ b/drivers/md/persistent-data/dm-btree-internal.h
@@ -38,7 +38,7 @@ struct node_header {
 
 struct btree_node {
        struct node_header header;
-       __le64 keys[0];
+       __le64 keys[];
 } __packed;