[PATCH] selinux: use GFP_ATOMIC in convert_context()

[GONG, Ruiqi]

The following BUG_ON was triggered on a hardware environment:

  SELinux: Converting 162 SID table entries...
  BUG: sleeping function called from invalid context at __might_sleep_rtos+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_rtos+0x168/0x17c
   __might_sleep_rtos+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 convert_context() (hooked by convert->func) might
sleep in a critial section of spin_lock_irqsave in
sidtab_context_to_sid(). Fix this problem by changing the memory
allocation in convert_context() from GFP_KERNEL to GFP_ATOMIC.

Reported-by: Tan Ninghao <tanninghao1@xxxxxxxxxx>
Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance")
Signed-off-by: GONG, Ruiqi <gongruiqi1@xxxxxxxxxx>
---
 security/selinux/ss/services.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index fe5fcf571c56..523876bb7df3 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2036,7 +2036,7 @@ static int convert_context(struct context *oldc, struct context *newc, void *p)
 	args = p;
 
 	if (oldc->str) {
-		s = kstrdup(oldc->str, GFP_KERNEL);
+		s = kstrdup(oldc->str, GFP_ATOMIC);
 		if (!s)
 			return -ENOMEM;
 
-- 
2.25.1