smack: use GFP_NOFS while holding inode_smack::smk_lock

BugLink: https://bugs.launchpad.net/bugs/1848598

commit e5bfad3d upstream.

inode_smack::smk_lock is taken during smack_d_instantiate(), which is
called during a filesystem transaction when creating a file on ext4.
Therefore to avoid a deadlock, all code that takes this lock must use
GFP_NOFS, to prevent memory reclaim from waiting for the filesystem
transaction to complete.

Reported-by: syzbot+0eefc1e06a77d327a056@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

security/smack/smack_access.c

@@ -474,7 +474,7 @@ char *smk_parse_smack(const char *string, int len)
 	if (i == 0 || i >= SMK_LONGLABEL)
 		return ERR_PTR(-EINVAL);
 
-	smack = kzalloc(i + 1, GFP_KERNEL);
+	smack = kzalloc(i + 1, GFP_NOFS);
 	if (smack == NULL)
 		return ERR_PTR(-ENOMEM);
 
@@ -545,7 +545,7 @@ struct smack_known *smk_import_entry(const char *string, int len)
 	if (skp != NULL)
 		goto freeout;
 
-	skp = kzalloc(sizeof(*skp), GFP_KERNEL);
+	skp = kzalloc(sizeof(*skp), GFP_NOFS);
 	if (skp == NULL) {
 		skp = ERR_PTR(-ENOMEM);
 		goto freeout;

security/smack/smack_lsm.c

@@ -268,7 +268,7 @@ static struct smack_known *smk_fetch(const char *name, struct inode *ip,
 	if (ip->i_op->getxattr == NULL)
 		return ERR_PTR(-EOPNOTSUPP);
 
-	buffer = kzalloc(SMK_LONGLABEL, GFP_KERNEL);
+	buffer = kzalloc(SMK_LONGLABEL, GFP_NOFS);
 	if (buffer == NULL)
 		return ERR_PTR(-ENOMEM);