From: Oleg Drokin <green@linuxhacker.ru>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Jeff Layton <jlayton@poochiereds.net>,
linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nfsd: Make creates return EEXIST correctly instead of EPERM
Date: Fri, 8 Jul 2016 17:53:19 -0400 [thread overview]
Message-ID: <DFD42803-99B2-4844-AAD3-0707E0F7DC66@linuxhacker.ru> (raw)
In-Reply-To: <20160708205413.GC11269@fieldses.org>
On Jul 8, 2016, at 4:54 PM, J. Bruce Fields wrote:
> On Thu, Jul 07, 2016 at 09:47:46PM -0400, Oleg Drokin wrote:
>> It looks like we are bit overzealous about failing mkdir/create/mknod
>> with permission denied if the parent dir is not writeable.
>> Need to make sure the name does not exist first, because we need to
>> return EEXIST in that case.
>>
>> Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
>> ---
>> A very similar problem exists with symlinks, but the patch is more
>> involved, so assuming this one is ok, I'll send a symlink one separately.
>> fs/nfsd/nfs4proc.c | 6 +++++-
>> fs/nfsd/vfs.c | 11 ++++++++++-
>> 2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
>> index de1ff1d..0067520 100644
>> --- a/fs/nfsd/nfs4proc.c
>> +++ b/fs/nfsd/nfs4proc.c
>> @@ -605,8 +605,12 @@ nfsd4_create(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>
>> fh_init(&resfh, NFS4_FHSIZE);
>>
>> + /*
>> + * We just check thta parent is accessible here, nfsd_* do their
>> + * own access permission checks
>> + */
>> status = fh_verify(rqstp, &cstate->current_fh, S_IFDIR,
>> - NFSD_MAY_CREATE);
>> + NFSD_MAY_EXEC);
>> if (status)
>> return status;
>>
>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>> index 6fbd81e..6a45ec6 100644
>> --- a/fs/nfsd/vfs.c
>> +++ b/fs/nfsd/vfs.c
>> @@ -1161,7 +1161,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
>> if (isdotent(fname, flen))
>> goto out;
>>
>> - err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
>> + /*
>> + * Even though it is a create, first we see if we are even allowed
>> + * to peek inside the parent
>> + */
>> + err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC);
>
> Looks like in the v3 case we haven't actually locked the directory yet
> at this point so this check is a little race-prone.
In reality this check is not really needed, I suspect.
When we call vfs_create/mknod/mkdir later on, it has it's own permission check
anyway so if there was a race and somebody changed dir access in the middle,
there's going to be another check anyway and it would be caught.
Unless there's some weird server-side permission wiggling as well that makes it
ineffective, but I imagine that one cannot really change in a racy way?
> I wonder why the code's structured that way--it's confusing.
Probably years of accumulated "damage" ;)
> --b.
>
>> if (err)
>> goto out;
>>
>> @@ -1211,6 +1215,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
>> goto out;
>> }
>>
>> + /* Now let's see if we actually have permissions to create */
>> + err = nfsd_permission(rqstp, fhp->fh_export, dentry, NFSD_MAY_CREATE);
>> + if (err)
>> + goto out;
>> +
>> if (!(iap->ia_valid & ATTR_MODE))
>> iap->ia_mode = 0;
>> iap->ia_mode = (iap->ia_mode & S_IALLUGO) | type;
>> --
>> 2.7.4
next prev parent reply other threads:[~2016-07-08 21:53 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-08 1:47 [PATCH] nfsd: Make creates return EEXIST correctly instead of EPERM Oleg Drokin
2016-07-08 11:02 ` Jeff Layton
2016-07-08 15:14 ` Oleg Drokin
2016-07-08 15:53 ` Jeff Layton
2016-07-08 15:59 ` Oleg Drokin
2016-07-08 16:17 ` Jeff Layton
2016-07-08 16:28 ` Oleg Drokin
2016-07-09 2:52 ` Al Viro
2016-07-09 2:58 ` Oleg Drokin
2016-07-09 3:13 ` Al Viro
2016-07-08 16:04 ` J. Bruce Fields
2016-07-08 16:16 ` Oleg Drokin
2016-07-08 20:49 ` J. Bruce Fields
2016-07-08 21:47 ` Oleg Drokin
2016-07-09 3:10 ` Al Viro
2016-07-09 3:41 ` Oleg Drokin
2016-07-13 19:00 ` J. Bruce Fields
2016-07-08 20:54 ` J. Bruce Fields
2016-07-08 21:53 ` Oleg Drokin [this message]
2016-07-21 20:34 ` J. Bruce Fields
2016-07-21 20:37 ` Oleg Drokin
2016-07-22 1:57 ` J. Bruce Fields
2016-07-22 6:35 ` Oleg Drokin
2016-07-22 10:55 ` J. Bruce Fields
2016-07-22 15:13 ` Oleg Drokin
2016-07-22 17:48 ` J. Bruce Fields
2016-07-22 17:48 ` [PATCH 1/7] nfsd: Make creates return EEXIST instead of EACCES J. Bruce Fields
2016-07-22 17:48 ` [PATCH 2/7] nfsd: remove redundant zero-length check from create J. Bruce Fields
2016-07-22 17:48 ` [PATCH 3/7] nfsd: remove redundant i_lookup check J. Bruce Fields
2016-07-24 0:22 ` Al Viro
2016-07-24 12:10 ` J. Bruce Fields
2016-07-24 14:23 ` Al Viro
2016-07-24 20:21 ` J. Bruce Fields
2016-07-22 17:48 ` [PATCH 4/7] nfsd: reorganize nfsd_create J. Bruce Fields
2016-07-22 17:48 ` [PATCH 5/7] nfsd: remove unnecessary positive-dentry check J. Bruce Fields
2016-07-22 17:48 ` [PATCH 6/7] nfsd: clean up bad-type check in nfsd_create_locked J. Bruce Fields
2016-07-22 17:48 ` [PATCH 7/7] nfsd: drop unnecessary MAY_EXEC check from create J. Bruce Fields
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