require rollback permission when force receive

Force receive (zfs receive -F) can rollback or destroy snapshots and
file systems that do not exist on the sending side (see zfs-receive man
page). This means an user having the receive permission can effectively
delete data on receiving side, even if such user does not have explicit
rollback or destroy permissions.

This patch add the rollback permission requirement for force receive.
To avoid changing current default behavior, a new tunable
zfs_recv_force_needs_perm is introduced. When set to 0 (default) the
new permission check is disabled. When set to 1 rollback permission
requirement is enabled.

Fixes #16943

Signed-off-by: Gionatan Danti <[email protected]>

Author: shodanshok

man/man4/zfs.4

@@ -2188,6 +2188,9 @@ If there is an error during healing, the healing receive is not
 terminated instead it moves on to the next record.
 .El
 .
+.It Sy zfs_recv_force_needs_perm Ns = Ns Sy 0 Pq int
+When not zero, force receive (zfs recv -F) requires rollback permission.
+.
 .It Sy zfs_override_estimate_recordsize Ns = Ns Sy 0 Ns | Ns 1 Pq uint
 Setting this variable overrides the default logic for estimating block
 sizes when doing a

man/man8/zfs-allow.8

@@ -207,7 +207,7 @@ load-key	subcommand	Allows loading and unloading of encryption key (see \fBzfs l
 change-key	subcommand	Allows changing an encryption key via \fBzfs change-key\fR.
 mount	subcommand	Allows mounting/umounting ZFS datasets
 promote	subcommand	Must also have the \fBmount\fR and \fBpromote\fR ability in the origin file system
-receive	subcommand	Must also have the \fBmount\fR and \fBcreate\fR ability
+receive	subcommand	Must also have the \fBmount\fR and \fBcreate\fR ability; must also have the \fBrollback\fR ability if \fBzfs receive -F\fR (force receive) is used and \fBzfs_recv_force_needs_perm\fR is set to 1.
 release	subcommand	Allows releasing a user hold which might destroy the snapshot
 rename	subcommand	Must also have the \fBmount\fR and \fBcreate\fR ability in the new parent
 rollback	subcommand	Must also have the \fBmount\fR ability

module/zfs/zfs_ioctl.c

@@ -238,6 +238,11 @@ uint64_t zfs_max_nvlist_src_size = 0;
  */
 static uint64_t zfs_history_output_max = 1024 * 1024;
 
+/*
+ * zfs_recv_force_needs_perm: if true, force receive (-F) requires rollback permission
+ */
+static int zfs_recv_force_needs_perm = 0;
+
 uint_t zfs_allow_log_key;
 
 /* DATA_TYPE_ANY is used when zkey_type can vary. */
@@ -908,6 +913,12 @@ zfs_secpolicy_recv(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 	    ZFS_DELEG_PERM_MOUNT, cr)) != 0)
 		return (error);
 
+	/* Forced receive can rollback or destroy snapshots */
+	if (zfs_recv_force_needs_perm && zc->zc_guid &&
+	    (error = zfs_secpolicy_write_perms(zc->zc_name,
+	    ZFS_DELEG_PERM_ROLLBACK, cr)) != 0)
+		return (error);
+
 	return (zfs_secpolicy_write_perms(zc->zc_name,
 	    ZFS_DELEG_PERM_CREATE, cr));
 }
@@ -8177,3 +8188,6 @@ ZFS_MODULE_PARAM(zfs, zfs_, max_nvlist_src_size, U64, ZMOD_RW,
 
 ZFS_MODULE_PARAM(zfs, zfs_, history_output_max, U64, ZMOD_RW,
 	"Maximum size in bytes of ZFS ioctl output that will be logged");
+
+ZFS_MODULE_PARAM(zfs, zfs_, recv_force_needs_perm, INT, ZMOD_RW,
+	"Force receive (-F) requires rollback permission");