smackfs: use __GFP_NOFAIL for smk_cipso_doi()

syzbot is reporting kernel panic at smk_cipso_doi() due to memory
allocation fault injection [1]. The reason for need to use panic() was
not explained. But since no fix was proposed for 18 months, for now
let's use __GFP_NOFAIL for utilizing syzbot resource on other bugs.

Link: https://syzkaller.appspot.com/bug?extid=89731ccb6fec15ce1c22 [1]
Reported-by: Nsyzbot <syzbot+89731ccb6fec15ce1c22@syzkaller.appspotmail.com>
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NCasey Schaufler <casey@schaufler-ca.com>

security/smack/smackfs.c

@@ -693,9 +693,7 @@ static void smk_cipso_doi(void)
 		printk(KERN_WARNING "%s:%d remove rc = %d\n",
 		       __func__, __LINE__, rc);
 
-	doip = kmalloc(sizeof(struct cipso_v4_doi), GFP_KERNEL);
-	if (doip == NULL)
-		panic("smack:  Failed to initialize cipso DOI.\n");
+	doip = kmalloc(sizeof(struct cipso_v4_doi), GFP_KERNEL | __GFP_NOFAIL);
 	doip->map.std = NULL;
 	doip->doi = smk_cipso_doi_value;
 	doip->type = CIPSO_V4_MAP_PASS;