Re: [PATCH] ext2: Don't export ext2_mask_flags() to user space

From: Mike Frysinger <vapier@gentoo.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Ted Ts'o" <tytso@mit.edu>,
	Artem Bityutskiy <dedekind1@gmail.com>,
	Thierry Reding <thierry.reding@avionic-design.de>,
	Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH] ext2: Don't export ext2_mask_flags() to user space
Date: Sat, 24 Mar 2012 02:50:38 -0400	[thread overview]
Message-ID: <CAMjpGUdnisfawUNThOu_+kbH54SWXCf6PhZwyWrV=B8SNjMRNg@mail.gmail.com> (raw)
In-Reply-To: <20120322173150.GY6589@ZenIV.linux.org.uk>

On Thu, Mar 22, 2012 at 13:31, Al Viro wrote:
> On Thu, Mar 22, 2012 at 12:28:25PM -0400, Ted Ts'o wrote:
>> On Thu, Mar 22, 2012 at 08:00:41AM +0200, Artem Bityutskiy wrote:
>> > On Thu, 2012-03-22 at 06:53 +0100, Thierry Reding wrote:
>> > > What's the recommended fix for packages that cannot or will not use
>> > > libext2fs, like busybox? Copy the required parts into a private header
>> > > and use that instead?
>> >
>> > The normal way is to just keep a private copy of the whole header file.
>> > Because the on-disk format stays compatible, those programs do not have
>> > to update the header very often - only rarely if they want to support
>> > some new feature.
>>
>> Even if they're not iwlling to use libext2fs (for space reasons, I
>> would assume?  It can't be because of license compatibility issues
>> since they are both GPLv2), they could just simply grab the ext2_fs.h
>> from e2fsprogs.  That has all of the file system definitions for ext2,
>> ext3, and ext4.
>
> Ho-hum...  Then we could kill a lot of lines in include/linux/ext2_fs.h.
> I wonder how much of what remains has any business being outside of
> fs/ext2, actually - AFAICS, there are very few places that might possibly
> care:
>
> arch/blackfin/kernel/setup.c:595:       if (*((unsigned short *)(mtd_phys + 0x438)) == EXT2_SUPER_MAGIC)
> fs/nfsd/nfs3proc.c:599:         case EXT2_SUPER_MAGIC:
> fs/nfsd/nfs3proc.c:600:                 resp->p_link_max = EXT2_LINK_MAX;
> fs/nfsd/nfs3proc.c:601:                 resp->p_name_max = EXT2_NAME_LEN;
> init/do_mounts_rd.c:57: struct ext2_super_block *ext2sb;
> init/do_mounts_rd.c:70: ext2sb = (struct ext2_super_block *) buf;
> init/do_mounts_rd.c:153:        if (ext2sb->s_magic == cpu_to_le16(EXT2_SUPER_MAGIC)) {
> init/do_mounts_rd.c:155:                       "RAMDISK: ext2 filesystem found at block %d\n",
> init/do_mounts_rd.c:157:                nblocks = le32_to_cpu(ext2sb->s_blocks_count) <<
> init/do_mounts_rd.c:158:                        le32_to_cpu(ext2sb->s_log_block_size);
> security/selinux/hooks.c:2974:  case EXT2_IOC_GETFLAGS:
> security/selinux/hooks.c:2976:  case EXT2_IOC_GETVERSION:
> security/selinux/hooks.c:2980:  case EXT2_IOC_SETFLAGS:
> security/selinux/hooks.c:2982:  case EXT2_IOC_SETVERSION:
>
> and that's it.  blackfin and do_mounts_rd are doing the same thing (blackfin -
> buggy, AFAICS).

buggy how ?  they're not exactly the same as the Blackfin code is
setting things up for the uClinux MTD map.  it isn't parsing the
filesystem itself (ignoring the size extraction from the superblock).

> Looks like both are  asking for something along the lines of
> sector_t detect_ext2(void *image), returning 0 if it's not one and size in
> kilobytes if it is...

yes, that would be fine
-mike