Re: NFS client broken in Linus' tip

Trond Myklebust
2014-02-03T20:22:18Z

On Mon, 2014-02-03 at 10:45 -0500, Trond Myklebust wrote:
> On Feb 3, 2014, at 9:57, Christoph Hellwig <hch@infradead.org> wrote:
>
> > On Mon, Feb 03, 2014 at 09:17:30AM -0500, Trond Myklebust wrote:
> >> As I said above, that causes posix_acl_xattr_get() to return the wrong answer (ENODATA instead of EOPNOTSUPP).
> >
> > Is it really the wrong answer? How does userspace care wether this
> > server doesn't support ACLs at all or none is set? The resulting
> > behavior is the same.
>
> It will certainly cause acl_get_file() to behave differently than previously. I’ve no idea how that will affect applications, though.
>
> > If there's a good reason to care we might have to go with your patch,
> > but if we can avoid it I'd prefer to keep things simple.
>
> One alternative is to simply wrap posix_acl_xattr_get() in fs/nfs/nfs3acl.c, and have it check the value of nfs_server_capable(inode, NFS_CAP_ACLS) before returning ENODATA. That’s rather ugly too...

FWIW, here is the alternative patch. I've tested it, and it seems to
work.
8<---------------------------------------------------------------------
>From 2e527b12169a67e9cfcf43898ae4d15bcfa1ede9 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@primarydata.com>
Date: Mon, 3 Feb 2014 13:07:05 -0500
Subject: [PATCH] NFSv3: Fix return values for get_acl()

Ensure that nfs3_get_acl() returns NULL when the server doesn't support
POSIX acls. This ensures that posix_acl_create() does the right thing,
and applies the current_umask() to the mode before returning.

Add a wrapper around posix_acl_xattr_get() so that we continue to
return EOPNOTSUPP when the server doesn't support POSIX acls. Otherwise,
the NULL return from nfs3_get_acl() will cause ENODATA to be returned.

Also add the appropriate exports to posix_acl_xattr_get, posix_acl_xattr_set
and posix_acl_xattr_list to enable their use in the wrapper.

Reported-by: Russell King <linux@arm.linux.org.uk>
Link: http://lkml.kernel.org/r/20140130140834.GW15937@n2100.arm.linux.org.uk
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro viro@zeniv.linux.org.uk>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
fs/nfs/nfs3acl.c | 42 ++++++++++++++++++++++++++++++++++++-----
fs/posix_acl.c | 9 ++++++---
include/linux/posix_acl_xattr.h | 8 ++++++++
3 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/nfs3acl.c b/fs/nfs/nfs3acl.c
index 871d6eda8dba..d1bc84f22f64 100644
--- a/fs/nfs/nfs3acl.c
+++ b/fs/nfs/nfs3acl.c
@@ -28,8 +28,10 @@ struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
};
int status, count;

- if (!nfs_server_capable(inode, NFS_CAP_ACLS))
- return ERR_PTR(-EOPNOTSUPP);
+ if (!nfs_server_capable(inode, NFS_CAP_ACLS)) {
+ cache_no_acl(inode);
+ return NULL;
+ }

status = nfs_revalidate_inode(server, inode);
if (status < 0)
@@ -70,7 +72,7 @@ struct posix_acl *nfs3_get_acl(struct inode *inode, int type)
dprintk("NFS_V3_ACL extension not supported; disabling\n");
server->caps &= ~NFS_CAP_ACLS;
case -ENOTSUPP:
- status = -EOPNOTSUPP;
+ status = 0;
default:
goto getout;
}
@@ -242,8 +244,38 @@ fail:
return PTR_ERR(alloc);
}

+static int
+nfs_posix_acl_xattr_get(struct dentry *dentry, const char *name,
+ void *value, size_t size, int type)
+{
+ int ret;
+
+ ret = posix_acl_xattr_get(dentry, name, value, size, type);
+ /*
+ * This check is needed to override the ENODATA error that
+ * posix_acl_xattr_get will return if the acl probe fails.
+ */
+ if (!nfs_server_capable(dentry->d_inode, NFS_CAP_ACLS))
+ ret = -EOPNOTSUPP;
+ return ret;
+}
+
+static const struct xattr_handler nfs_posix_acl_access_xattr_handler = {
+ .prefix = POSIX_ACL_XATTR_ACCESS,
+ .flags = ACL_TYPE_ACCESS,
+ .get = nfs_posix_acl_xattr_get,
+ .set = posix_acl_xattr_set,
+};
+
+static const struct xattr_handler nfs_posix_acl_default_xattr_handler = {
+ .prefix = POSIX_ACL_XATTR_DEFAULT,
+ .flags = ACL_TYPE_DEFAULT,
+ .get = nfs_posix_acl_xattr_get,
+ .set = posix_acl_xattr_set,
+};
+
const struct xattr_handler *nfs3_xattr_handlers[] = {
- &posix_acl_access_xattr_handler,
- &posix_acl_default_xattr_handler,
+ &nfs_posix_acl_access_xattr_handler,
+ &nfs_posix_acl_default_xattr_handler,
NULL,
};
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 38bae5a0ea25..835167f92952 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -750,7 +750,7 @@ posix_acl_to_xattr(struct user_namespace *user_ns, const struct posix_acl *acl,
}
EXPORT_SYMBOL (posix_acl_to_xattr);

-static int
+int
posix_acl_xattr_get(struct dentry *dentry, const char *name,
void *value, size_t size, int type)
{
@@ -773,8 +773,9 @@ posix_acl_xattr_get(struct dentry *dentry, const char *name,

return error;
}
+EXPORT_SYMBOL_GPL(posix_acl_xattr_get);

-static int
+int
posix_acl_xattr_set(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags, int type)
{
@@ -809,8 +810,9 @@ out:
posix_acl_release(acl);
return ret;
}
+EXPORT_SYMBOL_GPL(posix_acl_xattr_set);

-static size_t
+size_t
posix_acl_xattr_list(struct dentry *dentry, char *list, size_t list_size,
const char *name, size_t name_len, int type)
{
@@ -832,6 +834,7 @@ posix_acl_xattr_list(struct dentry *dentry, char *list, size_t list_size,
memcpy(list, xname, size);
return size;
}
+EXPORT_SYMBOL_GPL(posix_acl_xattr_list);

const struct xattr_handler posix_acl_access_xattr_handler = {
.prefix = POSIX_ACL_XATTR_ACCESS,
diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
index 6f14ee295822..fc062003a456 100644
--- a/include/linux/posix_acl_xattr.h
+++ b/include/linux/posix_acl_xattr.h
@@ -69,6 +69,14 @@ struct posix_acl *posix_acl_from_xattr(struct user_namespace *user_ns,
int posix_acl_to_xattr(struct user_namespace *user_ns,
const struct posix_acl *acl, void *buffer, size_t size);

+int posix_acl_xattr_get(struct dentry *dentry, const char *name,
+ void *value, size_t size, int type);
+int posix_acl_xattr_set(struct dentry *dentry, const char *name,
+ const void *value, size_t size, int flags, int type);
+size_t posix_acl_xattr_list(struct dentry *dentry, char *list,
+ size_t list_size, const char *name,
+ size_t name_len, int type);
+
extern const struct xattr_handler posix_acl_access_xattr_handler;
extern const struct xattr_handler posix_acl_default_xattr_handler;

--
1.8.5.3

--
Trond Myklebust
Linux NFS client maintainer