Don't assert on nvlists larger than SPA_MAXBLOCKSIZE

Originally we asserted that all reads are less than SPA_MAXBLOCKSIZE
However, nvlists are not ZFS records, and are not limited to
SPA_MAXBLOCKSIZE.

Add a new environment variable, ZFS_SENDRECV_MAX_NVLIST, to allow the
user to specify the maximum size of the nvlist that can be sent or
received.
Default value: 4 * SPA_MAXBLOCKSIZE (64 MB)

Modify libzfs send routines to return a useful error if the send stream
will generate an nvlist that is beyond the maximum size.

Modify libzfs recv routines to add an explicit error message if the
nvlist is too large, rather than abort()ing.

Move the change the assert() to only trigger on data records

Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Closes #9616

lib/libzfs/libzfs_sendrecv.c

@@ -610,6 +610,18 @@ send_iterate_fs(zfs_handle_t *zhp, void *arg)
 	fnvlist_free(sd->snapprops);
 	fnvlist_free(sd->snapholds);
 
+	/* Do not allow the size of the properties list to exceed the limit */
+	if ((fnvlist_size(nvfs) + fnvlist_size(sd->fss)) >
+	    zhp->zfs_hdl->libzfs_max_nvlist) {
+		(void) fprintf(stderr, dgettext(TEXT_DOMAIN,
+		    "warning: cannot send %s@%s: the size of the list of "
+		    "snapshots and properties is too large to be received "
+		    "successfully.\n"
+		    "Select a smaller number of snapshots to send.\n"),
+		    zhp->zfs_name, sd->tosnap);
+		rv = EZFS_NOSPC;
+		goto out;
+	}
 	/* add this fs to nvlist */
 	(void) snprintf(guidstring, sizeof (guidstring),
 	    "0x%llx", (longlong_t)guid);
@@ -2015,6 +2027,21 @@ send_prelim_records(zfs_handle_t *zhp, const char *from, int fd,
 			return (zfs_error(zhp->zfs_hdl, EZFS_BADBACKUP,
 			    errbuf));
 		}
+		/*
+		 * Do not allow the size of the properties list to exceed
+		 * the limit
+		 */
+		if ((fnvlist_size(fss) + fnvlist_size(hdrnv)) >
+		    zhp->zfs_hdl->libzfs_max_nvlist) {
+			(void) snprintf(errbuf, sizeof (errbuf),
+			    dgettext(TEXT_DOMAIN, "warning: cannot send '%s': "
+			    "the size of the list of snapshots and properties "
+			    "is too large to be received successfully.\n"
+			    "Select a smaller number of snapshots to send.\n"),
+			    zhp->zfs_name);
+			return (zfs_error(zhp->zfs_hdl, EZFS_NOSPC,
+			    errbuf));
+		}
 		fnvlist_add_nvlist(hdrnv, "fss", fss);
 		VERIFY0(nvlist_pack(hdrnv, &packbuf, &buflen, NV_ENCODE_XDR,
 		    0));
@@ -2578,8 +2605,6 @@ recv_read(libzfs_handle_t *hdl, int fd, void *buf, int ilen,
 	int rv;
 	int len = ilen;
 
-	assert(ilen <= SPA_MAXBLOCKSIZE);
-
 	do {
 		rv = read(fd, cp, len);
 		cp += rv;
@@ -2613,6 +2638,11 @@ recv_read_nvlist(libzfs_handle_t *hdl, int fd, int len, nvlist_t **nvp,
 	if (buf == NULL)
 		return (ENOMEM);
 
+	if (len > hdl->libzfs_max_nvlist) {
+		zfs_error_aux(hdl, dgettext(TEXT_DOMAIN, "nvlist too large"));
+		return (ENOMEM);
+	}
+
 	err = recv_read(hdl, fd, buf, len, byteswap, zc);
 	if (err != 0) {
 		free(buf);
@@ -3783,6 +3813,7 @@ recv_skip(libzfs_handle_t *hdl, int fd, boolean_t byteswap)
 			}
 			payload_size =
 			    DRR_WRITE_PAYLOAD_SIZE(&drr->drr_u.drr_write);
+			assert(payload_size <= SPA_MAXBLOCKSIZE);
 			(void) recv_read(hdl, fd, buf,
 			    payload_size, B_FALSE, NULL);
 			break;

lib/libzfs/libzfs_util.c

@@ -1008,6 +1008,7 @@ libzfs_init(void)
 {
 	libzfs_handle_t *hdl;
 	int error;
+	char *env;
 
 	error = libzfs_load_module();
 	if (error) {
@@ -1055,6 +1056,15 @@ libzfs_init(void)
 	if (getenv("ZFS_PROP_DEBUG") != NULL) {
 		hdl->libzfs_prop_debug = B_TRUE;
 	}
+	if ((env = getenv("ZFS_SENDRECV_MAX_NVLIST")) != NULL) {
+		if ((error = zfs_nicestrtonum(hdl, env,
+		    &hdl->libzfs_max_nvlist))) {
+			errno = error;
+			return (NULL);
+		}
+	} else {
+		hdl->libzfs_max_nvlist = (SPA_MAXBLOCKSIZE * 4);
+	}
 
 	/*
 	 * For testing, remove some settable properties and features