linux-kernel - Re: [RFC] setxattr bugs

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Message-ID: <51113DE5.10008@schaufler-ca.com>
Date:	Tue, 05 Feb 2013 09:14:13 -0800
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Jeff Mahoney <jeffm@...e.com>
CC:	Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, Dave Kleikamp <shaggy@...nel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC] setxattr bugs

On 2/4/2013 6:14 PM, Jeff Mahoney wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 2/2/13 11:30 PM, Al Viro wrote:
>> * JFS, since 2005: setxattr(name, "system.posix_acl_access", NULL,
>> 0, 0) succeeds, creating an empty EA with "system.posix_acl_access"
>> as name. Validity checks should apply _after_ if (value == NULL) {
>> /* empty EA, do not remove */ value = ""; value_len = 0; } and not
>> before it. * reiserfs, since 2009: setxattr(name, attr_name, NULL,
>> 0, 0) is treated as removexattr(name, attr_name), not as emptying
>> given xattr.
>>
>> The question is, does either of those cross into "established 
>> weirdness in ABI" or are they still at the "bugs to be fixed"
>> stage?
> Since the behavior changed once already in 2009 I'd call it a bug.
> That code was in the SLES kernel for a while before then and I still
> haven't seen a bug report on it.
>
> - -Jeff
>
>> FWIW, I'm seriously tempted to stop passing NULL as the third
>> argument of ->setxattr(), essentially taking all those if (!value)
>> value = ""; pieces from individual ->setxattr() instances to
>> __vfs_setxattr_noperm() (all other callers of ->setxattr() never 
>> pass NULL data or 0 size, so it's irrelevant for them).  Would fix 
>> both jfs and reiserfs weirdness....
>>
>> Objections?

None from me. I know of no one using either of those filesystems
in ways I care about. There's a chance the SELinux crowd may care,
so I'm adding the LSM list. We're the primary consumer of xattrs.

>
> - -- 
> Jeff Mahoney
> SUSE Labs
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