bcachefs: Add a better limit for maximum number of buckets

The bucket_gens array is a single array allocation (one byte per
bucket), and kernel allocations are still limited to INT_MAX.

Check this limit to avoid failing the bucket_gens array allocation.

Reported-by: syzbot+b29f436493184ea42e2b@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs_format.h

@@ -591,6 +591,12 @@ struct bch_member {
 	__le64			btree_allocated_bitmap;
 };
 
+/*
+ * This limit comes from the bucket_gens array - it's a single allocation, and
+ * kernel allocation are limited to INT_MAX
+ */
+#define BCH_MEMBER_NBUCKETS_MAX	(INT_MAX - 64)
+
 #define BCH_MEMBER_V1_BYTES	56
 
 LE64_BITMASK(BCH_MEMBER_STATE,		struct bch_member, flags,  0,  4)

fs/bcachefs/errcode.h

@@ -175,6 +175,7 @@
 	x(EINVAL,			block_size_too_small)			\
 	x(EINVAL,			bucket_size_too_small)			\
 	x(EINVAL,			device_size_too_small)			\
+	x(EINVAL,			device_size_too_big)			\
 	x(EINVAL,			device_not_a_member_of_filesystem)	\
 	x(EINVAL,			device_has_been_removed)		\
 	x(EINVAL,			device_splitbrain)			\

fs/bcachefs/sb-members.c

@@ -124,9 +124,9 @@ static int validate_member(struct printbuf *err,
 			   struct bch_sb *sb,
 			   int i)
 {
-	if (le64_to_cpu(m.nbuckets) > LONG_MAX) {
-		prt_printf(err, "device %u: too many buckets (got %llu, max %lu)",
-			   i, le64_to_cpu(m.nbuckets), LONG_MAX);
+	if (le64_to_cpu(m.nbuckets) > BCH_MEMBER_NBUCKETS_MAX) {
+		prt_printf(err, "device %u: too many buckets (got %llu, max %u)",
+			   i, le64_to_cpu(m.nbuckets), BCH_MEMBER_NBUCKETS_MAX);
 		return -BCH_ERR_invalid_sb_members;
 	}
 

fs/bcachefs/super.c

@@ -1959,6 +1959,13 @@ int bch2_dev_resize(struct bch_fs *c, struct bch_dev *ca, u64 nbuckets)
 		goto err;
 	}
 
+	if (nbuckets > BCH_MEMBER_NBUCKETS_MAX) {
+		bch_err(ca, "New device size too big (%llu greater than max %u)",
+			nbuckets, BCH_MEMBER_NBUCKETS_MAX);
+		ret = -BCH_ERR_device_size_too_big;
+		goto err;
+	}
+
 	if (bch2_dev_is_online(ca) &&
 	    get_capacity(ca->disk_sb.bdev->bd_disk) <
 	    ca->mi.bucket_size * nbuckets) {