file reference counts can get corrupted

Callers of zfs_file_get and zfs_file_put can corrupt the reference
counts for the file structure resulting in a panic or a soft lockup.
When zfs send/recv runs, it will add a reference count to the
open file, and begin to send or recv the stream. If the file descriptor
is closed, then when dmu_recv_stream() or dmu_send() return we will
call zfs_file_put to remove the reference we placed on the file
structure. Unfortunately, because zfs_file_put() uses the file
descriptor to lookup the file structure, it may end up finding that
the file descriptor table no longer contains the file struct, thus
leaking the file structure. Or it might end up finding a file
descriptor for a different file and blindly updating its reference
counts. Other failure modes probably exists.

This change reworks the zfs_file_[get|put] interface to not rely
on the file descriptor but instead pass the zfs_file_t pointer around.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Mark Maybee <mark.maybee@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Co-authored-by: Allan Jude <allan@klarasystems.com>
Signed-off-by: George Wilson <gwilson@delphix.com>
External-issue: DLPX-76119
Closes #12299

include/sys/fm/util.h

@@ -31,6 +31,7 @@ extern "C" {
 #endif
 
 #include <sys/nvpair.h>
+#include <sys/zfs_file.h>
 
 /*
  * Shared user/kernel definitions for class length, error channel name,
@@ -96,8 +97,8 @@ extern void fm_nvprint(nvlist_t *);
 extern void zfs_zevent_post_cb(nvlist_t *nvl, nvlist_t *detector);
 extern int zfs_zevent_post(nvlist_t *, nvlist_t *, zevent_cb_t *);
 extern void zfs_zevent_drain_all(int *);
-extern int zfs_zevent_fd_hold(int, minor_t *, zfs_zevent_t **);
-extern void zfs_zevent_fd_rele(int);
+extern zfs_file_t *zfs_zevent_fd_hold(int, minor_t *, zfs_zevent_t **);
+extern void zfs_zevent_fd_rele(zfs_file_t *);
 extern int zfs_zevent_next(zfs_zevent_t *, nvlist_t **, uint64_t *, uint64_t *);
 extern int zfs_zevent_wait(zfs_zevent_t *);
 extern int zfs_zevent_seek(zfs_zevent_t *, uint64_t);

include/sys/zfs_file.h

@@ -22,6 +22,8 @@
 #ifndef	_SYS_ZFS_FILE_H
 #define	_SYS_ZFS_FILE_H
 
+#include <sys/zfs_context.h>
+
 #ifndef _KERNEL
 typedef struct zfs_file {
 	int f_fd;
@@ -55,8 +57,8 @@ int zfs_file_fallocate(zfs_file_t *fp, int mode, loff_t offset, loff_t len);
 loff_t zfs_file_off(zfs_file_t *fp);
 int zfs_file_unlink(const char *);
 
-int zfs_file_get(int fd, zfs_file_t **fp);
-void zfs_file_put(int fd);
+zfs_file_t *zfs_file_get(int fd);
+void zfs_file_put(zfs_file_t *fp);
 void *zfs_file_private(zfs_file_t *fp);
 
 #endif /* _SYS_ZFS_FILE_H */

include/sys/zfs_ioctl.h

@@ -566,7 +566,7 @@ typedef struct zfsdev_state {
 } zfsdev_state_t;
 
 extern void *zfsdev_get_state(minor_t minor, enum zfsdev_state_type which);
-extern int zfsdev_getminor(int fd, minor_t *minorp);
+extern int zfsdev_getminor(zfs_file_t *fp, minor_t *minorp);
 extern minor_t zfsdev_minor_alloc(void);
 
 extern uint_t zfs_fsyncer_key;

include/sys/zfs_onexit.h

@@ -51,8 +51,8 @@ extern void zfs_onexit_destroy(zfs_onexit_t *zo);
 
 #endif
 
-extern int zfs_onexit_fd_hold(int fd, minor_t *minorp);
-extern void zfs_onexit_fd_rele(int fd);
+extern zfs_file_t *zfs_onexit_fd_hold(int fd, minor_t *minorp);
+extern void zfs_onexit_fd_rele(zfs_file_t *);
 extern int zfs_onexit_add_cb(minor_t minor, void (*func)(void *), void *data,
     uint64_t *action_handle);