dmu: fix integer overflows

The params to the functions are uint64_t, but the offsets to memcpy
/ bcopy are calculated using 32bit ints. This patch changes them to
also be uint64_t so there isnt an overflow. PaX's Size Overflow
caught this when formatting a zvol.

Gentoo bug: #546490

PAX: offset: 1ffffb000 db->db_offset: 1ffffa000 db->db_size: 2000 size: 5000
PAX: size overflow detected in function dmu_read /var/tmp/portage/sys-fs/zfs-kmod-0.6.3-r1/work/zfs-zfs-0.6.3/module/zfs/../../module/zfs/dmu.c:781 cicus.366_146 max, count: 15
CPU: 1 PID: 2236 Comm: zvol/10 Tainted: P           O   3.17.7-hardened-r1 #1
Call Trace:
 [<ffffffffa0382ee8>] ? dsl_dataset_get_holds+0x9d58/0x343ce [zfs]
 [<ffffffff81a59c88>] dump_stack+0x4e/0x7a
 [<ffffffffa0393c2a>] ? dsl_dataset_get_holds+0x1aa9a/0x343ce [zfs]
 [<ffffffff81206696>] report_size_overflow+0x36/0x40
 [<ffffffffa02dba2b>] dmu_read+0x52b/0x920 [zfs]
 [<ffffffffa0373ad1>] zrl_is_locked+0x7d1/0x1ce0 [zfs]
 [<ffffffffa0364cd2>] zil_clean+0x9d2/0xc00 [zfs]
 [<ffffffffa0364f21>] zil_commit+0x21/0x30 [zfs]
 [<ffffffffa0373fe1>] zrl_is_locked+0xce1/0x1ce0 [zfs]
 [<ffffffff81a5e2c7>] ? __schedule+0x547/0xbc0
 [<ffffffffa01582e6>] taskq_cancel_id+0x2a6/0x5b0 [spl]
 [<ffffffff81103eb0>] ? wake_up_state+0x20/0x20
 [<ffffffffa0158150>] ? taskq_cancel_id+0x110/0x5b0 [spl]
 [<ffffffff810f7ff4>] kthread+0xc4/0xe0
 [<ffffffff810f7f30>] ? kthread_create_on_node+0x170/0x170
 [<ffffffff81a62fa4>] ret_from_fork+0x74/0xa0
 [<ffffffff810f7f30>] ? kthread_create_on_node+0x170/0x170

Signed-off-by: Jason Zaman <jason@perfinion.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#3333

module/zfs/dmu.c

@@ -764,7 +764,7 @@ dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 	 * handle that here as well.
 	 */
 	if (dn->dn_maxblkid == 0) {
-		int newsz = offset > dn->dn_datablksz ? 0 :
+		uint64_t newsz = offset > dn->dn_datablksz ? 0 :
 		    MIN(size, dn->dn_datablksz - offset);
 		bzero((char *)buf + newsz, size - newsz);
 		size = newsz;
@@ -784,16 +784,16 @@ dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 			break;
 
 		for (i = 0; i < numbufs; i++) {
-			int tocpy;
-			int bufoff;
+			uint64_t tocpy;
+			int64_t bufoff;
 			dmu_buf_t *db = dbp[i];
 
 			ASSERT(size > 0);
 
 			bufoff = offset - db->db_offset;
-			tocpy = (int)MIN(db->db_size - bufoff, size);
+			tocpy = MIN(db->db_size - bufoff, size);
 
-			bcopy((char *)db->db_data + bufoff, buf, tocpy);
+			(void) memcpy(buf, (char *)db->db_data + bufoff, tocpy);
 
 			offset += tocpy;
 			size -= tocpy;
@@ -819,14 +819,14 @@ dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 	    FALSE, FTAG, &numbufs, &dbp));
 
 	for (i = 0; i < numbufs; i++) {
-		int tocpy;
-		int bufoff;
+		uint64_t tocpy;
+		int64_t bufoff;
 		dmu_buf_t *db = dbp[i];
 
 		ASSERT(size > 0);
 
 		bufoff = offset - db->db_offset;
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		tocpy = MIN(db->db_size - bufoff, size);
 
 		ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);
 
@@ -1108,13 +1108,15 @@ dmu_read_req(objset_t *os, uint64_t object, struct request *req)
 
 	req_offset = 0;
 	for (i = 0; i < numbufs; i++) {
-		int tocpy, didcpy, bufoff;
+		uint64_t tocpy;
+		int64_t bufoff;
+		int didcpy;
 		dmu_buf_t *db = dbp[i];
 
 		bufoff = offset - db->db_offset;
 		ASSERT3S(bufoff, >=, 0);
 
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		tocpy = MIN(db->db_size - bufoff, size);
 		if (tocpy == 0)
 			break;
 
@@ -1156,13 +1158,15 @@ dmu_write_req(objset_t *os, uint64_t object, struct request *req, dmu_tx_t *tx)
 
 	req_offset = 0;
 	for (i = 0; i < numbufs; i++) {
-		int tocpy, didcpy, bufoff;
+		uint64_t tocpy;
+		int64_t bufoff;
+		int didcpy;
 		dmu_buf_t *db = dbp[i];
 
 		bufoff = offset - db->db_offset;
 		ASSERT3S(bufoff, >=, 0);
 
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		tocpy = MIN(db->db_size - bufoff, size);
 		if (tocpy == 0)
 			break;
 
@@ -1212,14 +1216,14 @@ dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
 		return (err);
 
 	for (i = 0; i < numbufs; i++) {
-		int tocpy;
-		int bufoff;
+		uint64_t tocpy;
+		int64_t bufoff;
 		dmu_buf_t *db = dbp[i];
 
 		ASSERT(size > 0);
 
 		bufoff = uio->uio_loffset - db->db_offset;
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		tocpy = MIN(db->db_size - bufoff, size);
 
 		if (xuio) {
 			dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
@@ -1263,14 +1267,14 @@ dmu_write_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size, dmu_tx_t *tx)
 		return (err);
 
 	for (i = 0; i < numbufs; i++) {
-		int tocpy;
-		int bufoff;
+		uint64_t tocpy;
+		int64_t bufoff;
 		dmu_buf_t *db = dbp[i];
 
 		ASSERT(size > 0);
 
 		bufoff = uio->uio_loffset - db->db_offset;
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		tocpy = MIN(db->db_size - bufoff, size);
 
 		ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);