[PATCH v2 3/4] cmd: gpt: fix calc_parts_list_len()

[Heinrich Schuchardt]

* Avoid incrementing by moving comma into strlen("uuid_disk=,") and
  considering NUL byte.
* Appending a UUID only adds UUID_STR_LEN bytes.
  Don't count the terminating NUL.
* The length of the hexadecimal representation of lba_int is
  2 * sizeof(lba_int).
* We don't use a 'MiB' postfix but a '0x' prefix.
* The uuid field is only needed if configured.

Fixes: 2fcaa413b3f6 ("gpt: harden set_gpt_info() against non NULL-terminated strings")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
v2:
	new patch
---
 cmd/gpt.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/cmd/gpt.c b/cmd/gpt.c
index 092f7defff..e7a53747fc 100644
--- a/cmd/gpt.c
+++ b/cmd/gpt.c
@@ -162,22 +162,29 @@ static bool found_key(const char *str, const char *key)
 	return result;
 }
 
+/**
+ * calc_parts_list_len() - get size of partition table description
+ *
+ * @numparts:	number of partitions
+ * Return:	string size including terminating NUL
+ */
 static int calc_parts_list_len(int numparts)
 {
-	int partlistlen = UUID_STR_LEN + 1 + strlen("uuid_disk=");
-	/* for the comma */
-	partlistlen++;
-
-	/* per-partition additions; numparts starts at 1, so this should be correct */
-	partlistlen += numparts * (strlen("name=,") + PART_NAME_LEN + 1);
+	/* number of hexadecimal digits of the lbaint_t representation */
+	const int lbaint_size = 2 * sizeof(lbaint_t);
+	int partlistlen;
+
+	/* media description including terminating NUL */
+	partlistlen = strlen("uuid_disk=;") + UUID_STR_LEN + 1;
+	/* per-partition descriptions; numparts */
+	partlistlen += numparts * (strlen("name=,") + PART_NAME_LEN);
 	/* see part.h for definition of struct disk_partition */
-	partlistlen += numparts * (strlen("start=MiB,") + sizeof(lbaint_t) + 1);
-	partlistlen += numparts * (strlen("size=MiB,") + sizeof(lbaint_t) + 1);
-	partlistlen += numparts * (strlen("uuid=;") + UUID_STR_LEN + 1);
-	/* for the terminating null */
-	partlistlen++;
-	debug("Length of partitions_list is %d for %d partitions\n", partlistlen,
-	      numparts);
+	partlistlen += numparts * (strlen("start=0x,") + lbaint_size);
+	partlistlen += numparts * (strlen("size=0x,") + lbaint_size);
+	if (IS_ENABLED(CONFIG_PARTITION_UUIDS))
+		partlistlen += numparts * (strlen("uuid=;") + UUID_STR_LEN);
+	debug("Length of partitions_list is %d for %d partitions\n",
+	      partlistlen, numparts);
 	return partlistlen;
 }
 
-- 
2.40.1