linux-ext4 - Re: [PATCH V4] mke2fs: disallow creating FS on a loop mounted file with no option

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Date:	Sat, 30 Nov 2013 12:35:45 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Kazuya Mio <k-mio@...jp.nec.com>
Cc:	"'Andreas Dilger'" <adilger@...ger.ca>, tytso@....edu,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH V4] mke2fs: disallow creating FS on a loop mounted file
 with no option

On Fri, Nov 29, 2013 at 03:25:31PM +0900, Kazuya Mio wrote:
> Ping?
> Any comments/suggestions will be welcome.

I /think/ it looks fine...

--D
> 
> Regards,
> Kazuya Mio
> 
> > 2013/11/07 15:18:05, k-mio@...jp.nec.com wrote:
> > 
> > When /etc/mtab is a symlink of /proc/mounts, mke2fs without -FF option
> > can create a filesystem on the image file that is mounted.
> > According to mke2fs man page, we should specify -FF option in this case.
> > 
> > This patch protects filesystem from unintended mke2fs caused by human error.
> > 
> > How to reproduce:
> >   # mke2fs -t ext4 -Fq fs.img
> >   # mount -o loop fs.img /mnt/mp1
> >   # mke2fs -t ext4 -Fq fs.img && echo "mke2fs success"
> >   mke2fs success
> > 
> > Signed-off-by: Kazuya Mio <k-mio@...jp.nec.com>
> > ---
> >  configure.in           |    1 +
> >  lib/ext2fs/ismounted.c |   41 +++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 42 insertions(+)
> > diff --git a/configure.in b/configure.in
> > index 049dc11..fef8d9b 100644
> > --- a/configure.in
> > +++ b/configure.in
> > @@ -920,6 +920,7 @@ AC_CHECK_HEADERS(m4_flatten([
> >  	linux/falloc.h
> >  	linux/fd.h
> >  	linux/major.h
> > +	linux/loop.h
> >  	net/if_dl.h
> >  	netinet/in.h
> >  	sys/disklabel.h
> > diff --git a/lib/ext2fs/ismounted.c b/lib/ext2fs/ismounted.c
> > index 2c1bd75..6c6ecff 100644
> > --- a/lib/ext2fs/ismounted.c
> > +++ b/lib/ext2fs/ismounted.c
> > @@ -21,6 +21,13 @@
> >  #ifdef HAVE_LINUX_FD_H
> >  #include <linux/fd.h>
> >  #endif
> > +#ifdef HAVE_LINUX_LOOP_H
> > +#include <linux/loop.h>
> > +#include <sys/ioctl.h>
> > +#ifdef HAVE_LINUX_MAJOR_H
> > +#include <linux/major.h>
> > +#endif /* HAVE_LINUX_MAJOR_H */
> > +#endif /* HAVE_LINUX_LOOP_H */
> >  #ifdef HAVE_MNTENT_H
> >  #include <mntent.h>
> >  #endif
> > @@ -35,6 +42,36 @@
> >  #include "ext2_fs.h"
> >  #include "ext2fs.h"
> > 
> > +/*
> > + * Check to see if a regular file is mounted.
> > + * If /etc/mtab/ is a symlink of /proc/mounts, you will need the following check
> > + * because the name in /proc/mounts is a loopback device not a regular file.
> > + */
> > +static int check_loop_mounted(const char *mnt_fsname, dev_t mnt_rdev,
> > +				dev_t file_dev, ino_t file_ino)
> > +{
> > +#if defined(HAVE_LINUX_LOOP_H) && defined(HAVE_LINUX_MAJOR_H)
> > +	struct loop_info64 loopinfo;
> > +	int loop_fd, ret;
> > +
> > +	if (major(mnt_rdev) == LOOP_MAJOR) {
> > +		loop_fd = open(mnt_fsname, O_RDONLY);
> > +		if (loop_fd < 0)
> > +			return -1;
> > +
> > +		ret = ioctl(loop_fd, LOOP_GET_STATUS64, &loopinfo);
> > +		close(loop_fd);
> > +		if (ret < 0)
> > +			return -1;
> > +
> > +		if (file_dev == loopinfo.lo_device &&
> > +				file_ino == loopinfo.lo_inode)
> > +			return 1;
> > +	}
> > +#endif /* defined(HAVE_LINUX_LOOP_H) && defined(HAVE_LINUX_MAJOR_H) */
> > +	return 0;
> > +}
> > +
> >  #ifdef HAVE_SETMNTENT
> >  /*
> >   * Helper function which checks a file in /etc/mtab format to see if a
> > @@ -82,6 +119,10 @@ static errcode_t check_mntent_file(const char *mtab_file, const char *file,
> >  #ifndef __GNU__
> >  				if (file_rdev && (file_rdev == st_buf.st_rdev))
> >  					break;
> > +				if (check_loop_mounted(mnt->mnt_fsname,
> > +						st_buf.st_rdev, file_dev,
> > +						file_ino) == 1)
> > +					break;
> >  #endif	/* __GNU__ */
> >  			} else {
> >  				if (file_dev && ((file_dev == st_buf.st_dev) &&
> > --
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> 
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