On Linux, when doing path lookup with LOOKUP_RCU, dentry and inode can
be dereferenced without refcounts and locks. For this reason, dentry and
inode must only be freed after RCU grace period.
However, zfs currently frees inode in zfs_inode_destroy synchronously
and we can't use GPL-only call_rcu() in zfs directly. Fortunately, on
Linux 5.2 and after, if we define sops->free_inode(), the kernel will do
call_rcu() for us.
This issue may be triggered more easily with init_on_free=1 boot
parameter:
BUG: kernel NULL pointer dereference, address: 0000000000000020
RIP: 0010:selinux_inode_permission+0x10e/0x1c0
Call Trace:
? show_trace_log_lvl+0x1be/0x2d9
? show_trace_log_lvl+0x1be/0x2d9
? show_trace_log_lvl+0x1be/0x2d9
? security_inode_permission+0x37/0x60
? __die_body.cold+0x8/0xd
? no_context+0x113/0x220
? exc_page_fault+0x6d/0x130
? asm_exc_page_fault+0x1e/0x30
? selinux_inode_permission+0x10e/0x1c0
security_inode_permission+0x37/0x60
link_path_walk.part.0.constprop.0+0xb5/0x360
? path_init+0x27d/0x3c0
path_lookupat+0x3e/0x1a0
filename_lookup+0xc0/0x1d0
? __check_object_size.part.0+0x123/0x150
? strncpy_from_user+0x4e/0x130
? getname_flags.part.0+0x4b/0x1c0
vfs_statx+0x72/0x120
? ioctl_has_perm.constprop.0.isra.0+0xbd/0x120
__do_sys_newlstat+0x39/0x70
? __x64_sys_ioctl+0x8d/0xd0
do_syscall_64+0x30/0x40
entry_SYSCALL_64_after_hwframe+0x62/0xc7
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Rob Norris <rob.norris@klarasystems.com>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Co-authored-by: Chunwei Chen <david.chen@nutanix.com>
Closes#17546
