dm ioctl: structs and parameter strings must not overlap

The NUL terminator for each target parameter string must precede the
following 'struct dm_target_spec'.  Otherwise, dm_split_args() might
corrupt this struct.  Furthermore, the first 'struct dm_target_spec'
must come after the 'struct dm_ioctl', as if it overlaps too much
dm_split_args() could corrupt the 'struct dm_ioctl'.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index e322fd490634fdf01ed1c32c660b390c421704ff..a92abbe9098143f9de4cb33a38e23435258b3418 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1391,7 +1391,7 @@ static inline blk_mode_t get_mode(struct dm_ioctl *param)
        return mode;
 }
 
-static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
+static int next_target(struct dm_target_spec *last, uint32_t next, const char *end,
                       struct dm_target_spec **spec, char **target_params)
 {
        static_assert(__alignof__(struct dm_target_spec) <= 8,
@@ -1402,7 +1402,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
         * sizeof(struct dm_target_spec) or more, as otherwise *last was
         * out of bounds already.
         */
-       size_t remaining = (char *)end - (char *)last;
+       size_t remaining = end - (char *)last;
 
        /*
         * There must be room for both the next target spec and the
@@ -1422,10 +1422,7 @@ static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
        *spec = (struct dm_target_spec *) ((unsigned char *) last + next);
        *target_params = (char *) (*spec + 1);
 
-       if (*spec < (last + 1))
-               return -EINVAL;
-
-       return invalid_str(*target_params, end);
+       return 0;
 }
 
 static int populate_table(struct dm_table *table,
@@ -1435,8 +1432,9 @@ static int populate_table(struct dm_table *table,
        unsigned int i = 0;
        struct dm_target_spec *spec = (struct dm_target_spec *) param;
        uint32_t next = param->data_start;
-       void *end = (void *) param + param_size;
+       const char *const end = (const char *) param + param_size;
        char *target_params;
+       size_t min_size = sizeof(struct dm_ioctl);
 
        if (!param->target_count) {
                DMERR("%s: no targets specified", __func__);
@@ -1444,6 +1442,13 @@ static int populate_table(struct dm_table *table,
        }
 
        for (i = 0; i < param->target_count; i++) {
+               const char *nul_terminator;
+
+               if (next < min_size) {
+                       DMERR("%s: next target spec (offset %u) overlaps %s",
+                             __func__, next, i ? "previous target" : "'struct dm_ioctl'");
+                       return -EINVAL;
+               }
 
                r = next_target(spec, next, end, &spec, &target_params);
                if (r) {
@@ -1451,6 +1456,15 @@ static int populate_table(struct dm_table *table,
                        return r;
                }
 
+               nul_terminator = memchr(target_params, 0, (size_t)(end - target_params));
+               if (nul_terminator == NULL) {
+                       DMERR("%s: target parameters not NUL-terminated", __func__);
+                       return -EINVAL;
+               }
+
+               /* Add 1 for NUL terminator */
+               min_size = (size_t)(nul_terminator - (const char *)spec) + 1;
+
                r = dm_table_add_target(table, spec->target_type,
                                        (sector_t) spec->sector_start,
                                        (sector_t) spec->length,