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Fix get_zfs_sb race with concurrent umount

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Certain ioctl operations will call get_zfs_sb, which will holds an active
count on sb without checking whether it's active or not. This will result
in use-after-free. We fix this by using atomic_inc_not_zero to make sure
we got an active sb.

P1                                          P2
---                                         ---
deactivate_locked_super(): s_active = 0
                                            zfs_sb_hold()
                                            ->get_zfs_sb(): s_active = 1
->zpl_kill_sb()
-->zpl_put_super()
--->zfs_umount()
---->zfs_sb_free(zsb)
                                            zfs_sb_rele(zsb)

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Chunwei Chen 2016-07-08 16:59:54 -07:00 committed by Brian Behlendorf
parent 590c9a0994
commit 061460dfe2
1 changed files with 3 additions and 3 deletions
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6
module/zfs/zfs_ioctl.c
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@ -1393,9 +1393,9 @@ get_zfs_sb(const char *dsname, zfs_sb_t **zsbp)
mutex_enter(&os->os_user_ptr_lock);
*zsbp = dmu_objset_get_user(os);
if (*zsbp && (*zsbp)->z_sb) {
atomic_inc(&((*zsbp)->z_sb->s_active));
} else {
/* bump s_active only when non-zero to prevent umount race */
if (*zsbp == NULL || (*zsbp)->z_sb == NULL ||
!atomic_inc_not_zero(&((*zsbp)->z_sb->s_active))) {
error = SET_ERROR(ESRCH);
}
mutex_exit(&os->os_user_ptr_lock);