linux-kernel - [PATCH] init: fix read-write root mount

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Message-ID: <20141120150859.GA3596@tucsk>
Date:	Thu, 20 Nov 2014 16:08:59 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH] init: fix read-write root mount

From: Miklos Szeredi <mszeredi@...e.cz>

If mount flags don't have MS_RDONLY, iso9660 returns EACCES without actually
checking if it's an iso image.

This tricks mount_block_root() into retrying with MS_RDONLY.  This results
in a read-only root despite the "rw" boot parameter if the actual
filesystem was checked after iso9660.

I believe the behavior of iso9660 is okay, while that of mount_block_root()
is not.  It should rather try all types without MS_RDONLY and only then
retry with MS_RDONLY.

This change also makes the code more robust against the case when EACCES is
returned despite MS_RDONLY, which would've resulted in a lockup.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
 init/do_mounts.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -395,8 +395,6 @@ void __init mount_block_root(char *name,
 			case 0:
 				goto out;
 			case -EACCES:
-				flags |= MS_RDONLY;
-				goto retry;
 			case -EINVAL:
 				continue;
 		}
@@ -419,6 +417,10 @@ void __init mount_block_root(char *name,
 #endif
 		panic("VFS: Unable to mount root fs on %s", b);
 	}
+	if (!(flags & MS_RDONLY)) {
+		flags |= MS_RDONLY;
+		goto retry;
+	}

 	printk("List of all partitions:\n");
 	printk_all_partitions();
--
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