linux-kernel - [PATCH] VFS: mount must return EACCES, not EROFS

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Date:	Fri, 20 Jun 2014 10:39:22 +0200
From:	Philippe De Muyter <phdm@...qel.be>
To:	linux-kernel@...r.kernel.org
Cc:	Philippe De Muyter <phdm@...qel.be>,
	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH] VFS: mount must return EACCES, not EROFS

mount must return EACCES, not EROFS, when one attempts to mount a
read-only filesystem in read-write mode, but the file-system layer
only transmits the error given by the block layer, and many block
drivers return EROFS in that case, so let's fix it in do_mount.

Actually it is only a small problem for a user using the mount(1)
command, because EROFS is actually a more explicit answer than
EACCES, but init/do_mounts.c checks only for EACCES, not EROFS,
to decide to retry to mount the root file-system in read-only mode,
and so we are left with an unbootable kernel, and with a cryptic
error message (*) if the root partition happens to be read-only

(*): VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2):
error -30

Signed-off-by: Philippe De Muyter <phdm@...qel.be>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Dave Chinner <david@...morbit.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-fsdevel@...r.kernel.org
---
 fs/namespace.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 182bc41..6291a3f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2411,6 +2411,8 @@ long do_mount(const char *dev_name, const char *dir_name,
 
 	retval = security_sb_mount(dev_name, &path,
 				   type_page, flags, data_page);
+	if (retval == -EROFS)
+		retval = -EACCES;
 	if (!retval && !may_mount())
 		retval = -EPERM;
 	if (retval)
-- 
1.7.5.3

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