selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context()

In the Linux kernel, the following vulnerability has been resolved:

selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context()

The following warning was triggered on a hardware environment:

SELinux: Converting 162 SID table entries...

BUG: sleeping function called from invalid context at

__might_sleep+0x60/0x74 0x0

in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 5943, name: tar

CPU: 7 PID: 5943 Comm: tar Tainted: P O 5.10.0 #1

Call trace:

dump_backtrace+0x0/0x1c8

show_stack+0x18/0x28

dump_stack+0xe8/0x15c

___might_sleep+0x168/0x17c

__might_sleep+0x60/0x74

__kmalloc_track_caller+0xa0/0x7dc

kstrdup+0x54/0xac

convert_context+0x48/0x2e4

sidtab_context_to_sid+0x1c4/0x36c

security_context_to_sid_core+0x168/0x238

security_context_to_sid_default+0x14/0x24

inode_doinit_use_xattr+0x164/0x1e4

inode_doinit_with_dentry+0x1c0/0x488

selinux_d_instantiate+0x20/0x34

security_d_instantiate+0x70/0xbc

d_splice_alias+0x4c/0x3c0

ext4_lookup+0x1d8/0x200 [ext4]

__lookup_slow+0x12c/0x1e4

walk_component+0x100/0x200

path_lookupat+0x88/0x118

filename_lookup+0x98/0x130

user_path_at_empty+0x48/0x60

vfs_statx+0x84/0x140

vfs_fstatat+0x20/0x30

__se_sys_newfstatat+0x30/0x74

__arm64_sys_newfstatat+0x1c/0x2c

el0_svc_common.constprop.0+0x100/0x184

do_el0_svc+0x1c/0x2c

el0_svc+0x20/0x34

el0_sync_handler+0x80/0x17c

el0_sync+0x13c/0x140

SELinux: Context system_u:object_r:pssp_rsyslog_log_t:s0:c0 is

not valid (left unmapped).

It was found that within a critical section of spin_lock_irqsave in

sidtab_context_to_sid(), convert_context() (hooked by

sidtab_convert_params.func) might cause the process to sleep via

allocating memory with GFP_KERNEL, which is problematic.

As Ondrej pointed out [1], convert_context()/sidtab_convert_params.func

has another caller sidtab_convert_tree(), which is okay with GFP_KERNEL.

Therefore, fix this problem by adding a gfp_t argument for

convert_context()/sidtab_convert_params.func and pass GFP_KERNEL/_ATOMIC

properly in individual callers.

[PM: wrap long BUG() output lines, tweak subject line]