[PATCH v2 1/2] disk/part.c: ensure strings in struct disk_partition are valid after successful get_info

[Rasmus Villemoes <ravi@prevas.dk>]

Not all ->get_info implementations necessarily populate all the string
members of struct disk_partition.

Currently, only part_get_info_by_type() (and thereby part_get_info)
ensure that the uuid strings are initialized; part_get_info_by_type()
and part_get_info_by_uuid() do not. In fact, the latter could lead to
a false positive match - if the ->get_info backend does not populate
info->uuid, stale contents in info could cause the strncasecmp() to
succeed.

None of the functions currently ensure that the ->name and ->type
strings are initialized.

Instead of forcing all callers of any of these functions to
pre-initialize info, or all implementations of the ->get_info method
to ensure there are valid C strings in all four fields, create a small
helper function and factor all invocations of ->get_info through that.

This also consolidates the -ENOSYS check and standardizes on using
log_debug() for reporting absence, instead of the current mix of
PRINTF and log_debug(). It does mean we have to special-case -ENOSYS
in the error cases inside the loops in the _by_uuid() and _by_name()
functions, but it's still a net win in #LOC.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
---
v2: new patch in v2.

 cmd/gpt.c      |  4 ++--
 disk/part.c    | 62 ++++++++++++++++++++++++++++----------------------
 include/part.h | 16 +++++++++++++
 3 files changed, 53 insertions(+), 29 deletions(-)

diff --git a/cmd/gpt.c b/cmd/gpt.c
index e18e5036a06..84221881c39 100644
--- a/cmd/gpt.c
+++ b/cmd/gpt.c
@@ -724,7 +724,7 @@ static int gpt_enumerate(struct blk_desc *desc)
 			continue;
 
 		for (i = 1; i < part_drv->max_entries; i++) {
-			ret = part_drv->get_info(desc, i, &pinfo);
+			ret = part_driver_get_info(part_drv, desc, i, &pinfo);
 			if (ret)
 				continue;
 
@@ -820,7 +820,7 @@ static int gpt_setenv(struct blk_desc *desc, const char *name)
 		int i;
 
 		for (i = 1; i < part_drv->max_entries; i++) {
-			ret = part_drv->get_info(desc, i, &pinfo);
+			ret = part_driver_get_info(part_drv, desc, i, &pinfo);
 			if (ret)
 				continue;
 
diff --git a/disk/part.c b/disk/part.c
index be2b45d5a29..194eccadb7b 100644
--- a/disk/part.c
+++ b/disk/part.c
@@ -72,6 +72,28 @@ struct part_driver *part_driver_lookup_type(struct blk_desc *desc)
 	return NULL;
 }
 
+static void disk_partition_clr(struct disk_partition *info)
+{
+	/* The common case is no UUID support */
+	disk_partition_clr_uuid(info);
+	disk_partition_clr_type_guid(info);
+	info->name[0] = '\0';
+	info->type[0] = '\0';
+}
+
+int part_driver_get_info(struct part_driver *drv, struct blk_desc *desc, int part,
+			 struct disk_partition *info)
+{
+	if (!drv->get_info) {
+		log_debug("## Driver %s does not have the get_info() method\n",
+			  drv->name);
+		return -ENOSYS;
+	}
+
+	disk_partition_clr(info);
+	return drv->get_info(desc, part, info);
+}
+
 int part_get_type_by_name(const char *name)
 {
 	struct part_driver *drv =
@@ -322,12 +344,9 @@ int part_get_info_by_type(struct blk_desc *desc, int part, int part_type,
 			  struct disk_partition *info)
 {
 	struct part_driver *drv;
+	int ret = -ENOENT;
 
 	if (blk_enabled()) {
-		/* The common case is no UUID support */
-		disk_partition_clr_uuid(info);
-		disk_partition_clr_type_guid(info);
-
 		if (part_type == PART_TYPE_UNKNOWN) {
 			drv = part_driver_lookup_type(desc);
 		} else {
@@ -339,18 +358,13 @@ int part_get_info_by_type(struct blk_desc *desc, int part, int part_type,
 			      desc->part_type);
 			return -EPROTONOSUPPORT;
 		}
-		if (!drv->get_info) {
-			PRINTF("## Driver %s does not have the get_info() method\n",
-			       drv->name);
-			return -ENOSYS;
-		}
-		if (drv->get_info(desc, part, info) == 0) {
+
+		ret = part_driver_get_info(drv, desc, part, info);
+		if (!ret)
 			PRINTF("## Valid %s partition found ##\n", drv->name);
-			return 0;
-		}
 	}
 
-	return -ENOENT;
+	return ret;
 }
 
 int part_get_info(struct blk_desc *desc, int part,
@@ -657,15 +671,12 @@ int part_get_info_by_name(struct blk_desc *desc, const char *name,
 	if (!part_drv)
 		return -1;
 
-	if (!part_drv->get_info) {
-		log_debug("## Driver %s does not have the get_info() method\n",
-			  part_drv->name);
-		return -ENOSYS;
-	}
-
 	for (i = 1; i < part_drv->max_entries; i++) {
-		ret = part_drv->get_info(desc, i, info);
+		ret = part_driver_get_info(part_drv, desc, i, info);
 		if (ret != 0) {
+			/* -ENOSYS means no ->get_info method. */
+			if (ret == -ENOSYS)
+				return ret;
 			/*
 			 * Partition with this index can't be obtained, but
 			 * further partitions might be, so keep checking.
@@ -695,15 +706,12 @@ int part_get_info_by_uuid(struct blk_desc *desc, const char *uuid,
 	if (!part_drv)
 		return -1;
 
-	if (!part_drv->get_info) {
-		log_debug("## Driver %s does not have the get_info() method\n",
-			  part_drv->name);
-		return -ENOSYS;
-	}
-
 	for (i = 1; i < part_drv->max_entries; i++) {
-		ret = part_drv->get_info(desc, i, info);
+		ret = part_driver_get_info(part_drv, desc, i, info);
 		if (ret != 0) {
+			/* -ENOSYS means no ->get_info method. */
+			if (ret == -ENOSYS)
+				return ret;
 			/*
 			 * Partition with this index can't be obtained, but
 			 * further partitions might be, so keep checking.
diff --git a/include/part.h b/include/part.h
index 6caaa6526aa..d940f8b5d0e 100644
--- a/include/part.h
+++ b/include/part.h
@@ -509,6 +509,22 @@ struct part_driver {
 	int (*test)(struct blk_desc *desc);
 };
 
+/**
+ * part_driver_get_info() - Call the part_driver's get_info method
+ *
+ * On success, string members of info are guaranteed to be properly
+ * initialized, though they may be empty.
+ *
+ * @drv:	Partition driver
+ * @desc:	Block device descriptor
+ * @part:	Partition number to read
+ * @info:	Returned partition information
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int part_driver_get_info(struct part_driver *drv, struct blk_desc *desc, int part,
+			 struct disk_partition *info);
+
 /* Declare a new U-Boot partition 'driver' */
 #define U_BOOT_PART_TYPE(__name)					\
 	ll_entry_declare(struct part_driver, __name, part_driver)
-- 
2.51.0