linux-kernel - Re: mount on tmpfs failing to parse context option

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Message-ID: <20191008012622.GP26530@ZenIV.linux.org.uk>
Date:   Tue, 8 Oct 2019 02:26:22 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Laura Abbott <labbott@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: mount on tmpfs failing to parse context option

On Mon, Oct 07, 2019 at 05:50:31PM -0700, Hugh Dickins wrote:

[sorry for being MIA - had been sick through the last week, just digging
myself from under piles of mail; my apologies]

> (tmpfs, very tiresomely, supports a NUMA "mpol" mount option which can
> have commas in it e.g "mpol=bind:0,2": which makes all its comma parsing
> awkward.  I assume that where the new mount API commits bend over to
> accommodate that peculiarity, they end up mishandling the comma in
> the context string above.)

	Dumber than that, I'm afraid.  mpol is the reason for having
->parse_monolithic() in the first place, all right, but the problem is
simply the lack of security_sb_eat_lsm_opts() call in it.

	Could you check if the following fixes that one?

diff --git a/mm/shmem.c b/mm/shmem.c
index 0f7fd4a85db6..8dcc8d04cbaf 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3482,6 +3482,12 @@ static int shmem_parse_options(struct fs_context *fc, void *data)
 {
 	char *options = data;
 
+	if (options) {
+		int err = security_sb_eat_lsm_opts(options, &fc->security);
+		if (err)
+			return err;
+	}
+
 	while (options != NULL) {
 		char *this_char = options;
 		for (;;) {