btrfs-progs: add extra chunk alignment checks

Recently we had a scrub use-after-free caused by unaligned chunk
length, although the fix was submitted, we may want to do extra checks
for a chunk's alignment.

This patch adds such check for the starting bytenr and length of a
chunk, to make sure they are properly aligned to 64K stripe boundary.

By default, the check only leads to a warning but is not treated as an
error, as we expect kernel to handle such unalignment without any
problem.

But if the new debug environmental variable,
BTRFS_PROGS_DEBUG_STRICT_CHUNK_ALIGNMENT, is specified, then we will
treat it as an error.  So that we can detect unexpected chunks from
btrfs-progs, and fix them before reaching the end users.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

check/common.h

@@ -78,6 +78,7 @@ struct chunk_record {
 	u32 io_align;
 	u32 io_width;
 	u32 sector_size;
+	bool unaligned;
 	struct stripe stripes[0];
 };
 

check/main.c

@@ -5265,6 +5265,9 @@ struct chunk_record *btrfs_new_chunk_record(struct extent_buffer *leaf,
 	rec->num_stripes = num_stripes;
 	rec->sub_stripes = btrfs_chunk_sub_stripes(leaf, ptr);
 
+	if (!IS_ALIGNED(rec->cache.start, BTRFS_STRIPE_LEN) ||
+	    !IS_ALIGNED(rec->cache.size, BTRFS_STRIPE_LEN))
+		rec->unaligned = true;
 	for (i = 0; i < rec->num_stripes; ++i) {
 		rec->stripes[i].devid =
 			btrfs_stripe_devid_nr(leaf, ptr, i);
@@ -8386,6 +8389,7 @@ int check_chunks(struct cache_tree *chunk_cache,
 	struct chunk_record *chunk_rec;
 	struct block_group_record *bg_rec;
 	struct device_extent_record *dext_rec;
+	bool strict_alignment = get_env_bool("BTRFS_DEBUG_STRICT_CHUNK_ALIGNMENT");
 	int err;
 	int ret = 0;
 
@@ -8393,6 +8397,22 @@ int check_chunks(struct cache_tree *chunk_cache,
 	while (chunk_item) {
 		chunk_rec = container_of(chunk_item, struct chunk_record,
 					 cache);
+		if (chunk_rec->unaligned && !silent) {
+			if (strict_alignment) {
+				error(
+		"chunk[%llu %llu) is not fully aligned to BTRFS_STRIPE_LEN (%u)",
+				      chunk_rec->cache.start,
+				      chunk_rec->cache.start + chunk_rec->cache.size,
+				      BTRFS_STRIPE_LEN);
+				ret = -EINVAL;
+			} else {
+				warning(
+		"chunk[%llu %llu) is not fully aligned to BTRFS_STRIPE_LEN (%u)",
+				      chunk_rec->cache.start,
+				      chunk_rec->cache.start + chunk_rec->cache.size,
+				      BTRFS_STRIPE_LEN);
+			}
+		}
 		err = check_chunk_refs(chunk_rec, block_group_cache,
 				       dev_extent_cache, silent);
 		if (err < 0)

check/mode-lowmem.c

@@ -4719,6 +4719,17 @@ static int check_chunk_item(struct extent_buffer *eb, int slot)
 	chunk = btrfs_item_ptr(eb, slot, struct btrfs_chunk);
 	length = btrfs_chunk_length(eb, chunk);
 	chunk_end = chunk_key.offset + length;
+	if (!IS_ALIGNED(chunk_key.offset, BTRFS_STRIPE_LEN) ||
+	    !IS_ALIGNED(length, BTRFS_STRIPE_LEN)) {
+		if (get_env_bool("BTRFS_PROGS_DEBUG_STRICT_CHUNK_ALIGNMENT")) {
+			error("chunk[%llu %llu) is not fully aligned to BTRFS_STRIPE_LEN (%u)",
+				chunk_key.offset, length, BTRFS_STRIPE_LEN);
+			err |= BYTES_UNALIGNED;
+			goto out;
+		}
+		warning("chunk[%llu %llu) is not fully aligned to BTRFS_STRIPE_LEN (%u)",
+			chunk_key.offset, length, BTRFS_STRIPE_LEN);
+	}
 	ret = btrfs_check_chunk_valid(eb, chunk, chunk_key.offset);
 	if (ret < 0) {
 		error("chunk[%llu %llu) is invalid", chunk_key.offset,

common/utils.c

@@ -956,6 +956,25 @@ u8 rand_u8(void)
 	return (u8)(rand_u32());
 }
 
+/*
+ * Parse a boolean value from an environment variable.
+ *
+ * As long as the environment variable is not set to "0", "n" or "\0",
+ * it would return true.
+ */
+bool get_env_bool(const char *env_name)
+{
+	char *env_value_str;
+
+	env_value_str = getenv(env_name);
+	if (!env_value_str)
+		return false;
+	if (env_value_str[0] == '0' || env_value_str[0] == 'n' ||
+	    env_value_str[0] == 0)
+		return false;
+	return true;
+}
+
 void btrfs_config_init(void)
 {
 	bconf.output_format = CMD_FORMAT_TEXT;

common/utils.h

@@ -117,6 +117,8 @@ u64 rand_u64(void);
 unsigned int rand_range(unsigned int upper);
 void init_rand_seed(u64 seed);
 
+bool get_env_bool(const char *env_name);
+
 char *btrfs_test_for_multiple_profiles(int fd);
 int btrfs_warn_multiple_profiles(int fd);
 void btrfs_warn_experimental(const char *str);