tracefs: Set the group ownership in apply_options() not parse_options()

stable inclusion
from stable-v5.10.103
commit 3a1dd56e566fa71419da2c145a6850e63f17fbf0
bugzilla: https://gitee.com/openeuler/kernel/issues/I56NE7

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a1dd56e566fa71419da2c145a6850e63f17fbf0

--------------------------------

commit 851e99eb upstream.

Al Viro brought it to my attention that the dentries may not be filled
when the parse_options() is called, causing the call to set_gid() to
possibly crash. It should only be called if parse_options() succeeds
totally anyway.

He suggested the logical place to do the update is in apply_options().

Link: https://lore.kernel.org/all/20220225165219.737025658@goodmis.org/
Link: https://lkml.kernel.org/r/20220225153426.1c4cab6b@gandalf.local.home

Cc: stable@vger.kernel.org
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>
Reported-by: NAl Viro <viro@zeniv.linux.org.uk>
Fixes: 48b27b6b ("tracefs: Set all files to the same group ownership as the mount option")
Signed-off-by: NSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/tracefs/inode.c

@@ -262,7 +262,6 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 			if (!gid_valid(gid))
 				return -EINVAL;
 			opts->gid = gid;
-			set_gid(tracefs_mount->mnt_root, gid);
 			break;
 		case Opt_mode:
 			if (match_octal(&args[0], &option))
@@ -289,7 +288,9 @@ static int tracefs_apply_options(struct super_block *sb)
 	inode->i_mode |= opts->mode;
 
 	inode->i_uid = opts->uid;
-	inode->i_gid = opts->gid;
+
+	/* Set all the group ids to the mount option */
+	set_gid(sb->s_root, opts->gid);
 
 	return 0;
 }