[PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Sage Weil]

Hi Miklos,

I found some time to track down the O_CREAT error code issue.  Patch is 
below.  Does this look correct?

I was reproducing with

 ceph-fuse mnt
 mkdir -p mnt/a
 cd mnt
 .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644

EACCES is expected, ENOENT was returned instead.

Thanks!
sage

(BTW: strangely, the correct value was returned if I traverse across 
mounts, e.g.

 mkdir -p mnt/a
 .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open mnt/a/foo O_RDONLY,O_CREAT 0644
)


>From d438bfcae681251c957bcd2b6a2559567faee218 Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@inktank.com>
Date: Wed, 15 Aug 2012 13:30:12 -0700
Subject: [PATCH] vfs: fix propagation of atomic_open create error on negative
 dentry

If ->atomic_open() returns -ENOENT, we take care to return the create
error (e.g., EACCES), if any.  Do the same when ->atomic_open() returns 1
and provides a negative dentry.

This fixes a regression where an unprivileged open O_CREAT fails with
ENOENT instead of EACCES, introduced with the new atomic_open code.  It
is tested by the open/08.t test in the pjd posix test suite, and was
observed on top of fuse (backed by ceph-fuse).

Signed-off-by: Sage Weil <sage@inktank.com>
---
 fs/namei.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 26c28ec..db76b86 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2489,6 +2489,10 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
 			dput(dentry);
 			dentry = file->f_path.dentry;
 		}
+		if (create_error && dentry->d_inode == NULL) {
+			error = create_error;
+			goto out;
+		}
 		goto looked_up;
 	}
 
-- 
1.7.9

Re: [PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Miklos Szeredi]

Sage Weil <sage@inktank.com> writes:

> Hi Miklos,
>
> I found some time to track down the O_CREAT error code issue.  Patch is 
> below.  Does this look correct?
>
> I was reproducing with
>
>  ceph-fuse mnt
>  mkdir -p mnt/a
>  cd mnt
>  .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644
>
> EACCES is expected, ENOENT was returned instead.

I don't quite undersdand what is happending here.

Why does ceph-fuse return ENOENT here?  Returning ENOENT for O_CREAT
only makes sense if the parent directory doesn't exist, but that's not
the case here.

Thanks,
Miklos

Re: [PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Miklos Szeredi]

Miklos Szeredi <miklos@szeredi.hu> writes:

> Sage Weil <sage@inktank.com> writes:
>
>> Hi Miklos,
>>
>> I found some time to track down the O_CREAT error code issue.  Patch is 
>> below.  Does this look correct?
>>
>> I was reproducing with
>>
>>  ceph-fuse mnt
>>  mkdir -p mnt/a
>>  cd mnt
>>  .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644
>>
>> EACCES is expected, ENOENT was returned instead.
>
> I don't quite undersdand what is happending here.
>
> Why does ceph-fuse return ENOENT here?  Returning ENOENT for O_CREAT
> only makes sense if the parent directory doesn't exist, but that's not
> the case here.

More specifically, the initial lookup will return ENOENT, that's fine.

But in that case fuse_atomic_open() will do a FUSE_CREATE for which
ENOENT is not the right answer.

Can you post the relevant part from the filesytem's debug log?

Thanks,
Miklos

Re: [PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Sage Weil]

On Thu, 16 Aug 2012, Miklos Szeredi wrote:
> Miklos Szeredi <miklos@szeredi.hu> writes:
> 
> > Sage Weil <sage@inktank.com> writes:
> >
> >> Hi Miklos,
> >>
> >> I found some time to track down the O_CREAT error code issue.  Patch is 
> >> below.  Does this look correct?
> >>
> >> I was reproducing with
> >>
> >>  ceph-fuse mnt
> >>  mkdir -p mnt/a
> >>  cd mnt
> >>  .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644
> >>
> >> EACCES is expected, ENOENT was returned instead.
> >
> > I don't quite undersdand what is happending here.
> >
> > Why does ceph-fuse return ENOENT here?  Returning ENOENT for O_CREAT
> > only makes sense if the parent directory doesn't exist, but that's not
> > the case here.
> 
> More specifically, the initial lookup will return ENOENT, that's fine.
> 
> But in that case fuse_atomic_open() will do a FUSE_CREATE for which
> ENOENT is not the right answer.

I didn't dig deeply into what fuse_lookup() itself was doing, but the 
short version is:

- namei.c's atomic_open() gets -EACCES from the may_o_create() check, sets 
create_error, and clears O_CREAT from the flags

- fuse_atomic_open() calls fuse_lookup(), which returns NULL and leaves 
entry->d_inode == NULL.  ceph-fuse's lookup method returned -ENOENT.  
fuse_lookup() is just hashing the negative dentry instead of returning 
ENOENT.

- fuse_atomic_open() sees O_CREAT is not set and calls finish_no_open().

- the existing ENOENT -> EACCES check in atomic_open() (below) fails 
because fuse_atomic_open() returned 1:

	if (error < 0) {
		if (create_error && error == -ENOENT)
			error = create_error;
		goto out;
	}

This patch just applies the same ENOENT->EACCES logic to the equivalent 
negative/null dentry case.

> Can you post the relevant part from the filesytem's debug log?

The relevant bit is

unique: 11, opcode: GETATTR (3), nodeid: 1, insize: 56, pid: 8502
   unique: 11, success, outsize: 120
unique: 12, opcode: LOOKUP (1), nodeid: 1, insize: 42, pid: 8502
   unique: 12, success, outsize: 144
unique: 13, opcode: GETATTR (3), nodeid: 1099511627776, insize: 56, pid: 8502
   unique: 13, success, outsize: 120
unique: 14, opcode: GETATTR (3), nodeid: 1099511627776, insize: 56, pid: 8502
   unique: 14, success, outsize: 120
unique: 15, opcode: LOOKUP (1), nodeid: 1099511627776, insize: 45, pid: 8502
   unique: 15, error: -2 (No such file or directory), outsize: 16

Thanks-
sage

Re: [PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Miklos Szeredi]

Sage Weil <sage-4GqslpFJ+cxBDgjK7y7TUQ@public.gmane.org> writes:

> On Thu, 16 Aug 2012, Miklos Szeredi wrote:
>> Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org> writes:
>> 
>> > Sage Weil <sage-4GqslpFJ+cxBDgjK7y7TUQ@public.gmane.org> writes:
>> >
>> >> Hi Miklos,
>> >>
>> >> I found some time to track down the O_CREAT error code issue.  Patch is 
>> >> below.  Does this look correct?
>> >>
>> >> I was reproducing with
>> >>
>> >>  ceph-fuse mnt
>> >>  mkdir -p mnt/a
>> >>  cd mnt
>> >>  .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644
>> >>
>> >> EACCES is expected, ENOENT was returned instead.
>> >
>> > I don't quite undersdand what is happending here.
>> >
>> > Why does ceph-fuse return ENOENT here?  Returning ENOENT for O_CREAT
>> > only makes sense if the parent directory doesn't exist, but that's not
>> > the case here.
>> 
>> More specifically, the initial lookup will return ENOENT, that's fine.
>> 
>> But in that case fuse_atomic_open() will do a FUSE_CREATE for which
>> ENOENT is not the right answer.
>
> I didn't dig deeply into what fuse_lookup() itself was doing, but the 
> short version is:
>
> - namei.c's atomic_open() gets -EACCES from the may_o_create() check, sets 
> create_error, and clears O_CREAT from the flags
>
> - fuse_atomic_open() calls fuse_lookup(), which returns NULL and leaves 
> entry->d_inode == NULL.  ceph-fuse's lookup method returned -ENOENT.  
> fuse_lookup() is just hashing the negative dentry instead of returning 
> ENOENT.
>
> - fuse_atomic_open() sees O_CREAT is not set and calls finish_no_open().
>
> - the existing ENOENT -> EACCES check in atomic_open() (below) fails 
> because fuse_atomic_open() returned 1:
>
> 	if (error < 0) {
> 		if (create_error && error == -ENOENT)
> 			error = create_error;
> 		goto out;
> 	}
>
> This patch just applies the same ENOENT->EACCES logic to the equivalent 
> negative/null dentry case.

Okay, I get it now.

Yes, your patch looks correct.  I'll queue it up with the other
atomic-open fixes.

Thanks,
Miklos

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Re: [fuse-devel] [PATCH] vfs: fix propagation of atomic_open create error on negative dentry

[Jean-Pierre André]

Hi,

Miklos Szeredi wrote:
> Sage Weil<sage@inktank.com>  writes:
>
>
>> Hi Miklos,
>>
>> I found some time to track down the O_CREAT error code issue.  Patch is
>> below.  Does this look correct?
>>
>> I was reproducing with
>>
>>   ceph-fuse mnt
>>   mkdir -p mnt/a
>>   cd mnt
>>   .../pjd-fstest-20080816/fstest -u 65534 -g 65534 open a/foo O_RDONLY,O_CREAT 0644
>>
>> EACCES is expected, ENOENT was returned instead.
>>
> I don't quite undersdand what is happending here.
>
> Why does ceph-fuse return ENOENT here?  Returning ENOENT for O_CREAT
> only makes sense if the parent directory doesn't exist, but that's not
> the case here.
>

In this test, the parent directory exists, but it is not
writable by the process which tries to create the file.

According to opengroup, from
http://pubs.opengroup.org/onlinepubs/000095399/functions/open.html


    The /open/() function shall fail if:

    [EACCES]
        Search permission is denied on a component of the path prefix,
        or the file exists and the permissions specified by /oflag/ are
        denied, or *the file does not exist and write permission is
        denied for the parent directory of the file to be created*, or
        O_TRUNC is specified and write permission is denied.


Regards

Jean-Pierre