Re: [PATCH v2 0/3] fuse: Add support for mounts from pid/user namespaces

Eric W. Biederman
2014-09-27T01:42:05Z

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Seth Forshee <seth.forshee@canonical.com> writes:

> On Thu, Sep 25, 2014 at 12:14:01PM -0700, Eric W. Biederman wrote:

>> Sorry iattr_to_setattr look for from_kuid and from_kgid.
>>
>> The call path is
>> fuse_setattr
>> fuse_do_setattr
>> iattr_to_fattr.
>
> Bah. Sorry, I misread that originally and thought you were talking about
> something outside of fuse. And I was looking at a tree with my fuse
> changes, so of course I wouldn't have found it.
>
> Actually in 3.17-rc6 I still don't see that iattr_to_fattr (I assume
> this is what you meant) checks the results of the conversion (not that
> it really needs to since it uses init_user_ns), nor any use of EOVERFLOW
> in fuse. Anyway, it's not really important.

True. I also goofed up in that I was looking at the wrong tree. My
tree had all of my preliminary fuse patches I worked up a while ago
applied so I did have the error handling in there.

> Well, unless you say otherwise I guess I'll leave it -EINVAL to be
> consistent with chown_common().

That sounds like a good plan.

>> I am on the fence about what to do when a uid from the filesystem server
>> or for other filesystems the on-disk data structures does not map, but
>> make_bad_inode is simpler in conception. So make_bad_inode seems like
>> a good place to start. For fuse especially this isn't hard because
>> the make_bad_inode calls are already there to handle a change in i_mode.
>
> I agree that if we're unsure then make_bad_inode is a more logical place
> to start, since it's easier to loosen the restrictions later than to
> tighten them. I've got an initiail implementation that I'm in the
> process of testing. If you want to take a look I've pushed it to:
>
> git://kernel.ubuntu.com/sforshee/linux.git fuse-userns

Thanks. If I can scrape together enough focus I will look at it.

As a second best thing here are my prototype from when I was looking at
performing this fuse conversion last. Given that you had missed
checking the from_kuid permission checks, it might be worth comparing
and seeing if there is something else in these patches that would be
worth including.

Eric

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>From 94195ce5b06915846d14eaa35d9274c0315b46a0 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Thu, 4 Oct 2012 13:34:45 -0700
Subject: [PATCH 1/4] userns: Allow for fuse filesystems outside the initial user
namespace

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/fuse/dev.c | 10 +++++-----
fs/fuse/dir.c | 41 ++++++++++++++++++++++++++++++-----------
fs/fuse/fuse_i.h | 3 +++
fs/fuse/inode.c | 10 ++++++++--
4 files changed, 46 insertions(+), 18 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ca887314aba9..e01f30c51b3c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -124,10 +124,10 @@ static void __fuse_put_request(struct fuse_req *req)
atomic_dec(&req->count);
}

-static void fuse_req_init_context(struct fuse_req *req)
+static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
{
- req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
- req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
+ req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
+ req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
req->in.h.pid = current->pid;
}

@@ -168,7 +168,7 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
goto out;
}

- fuse_req_init_context(req);
+ fuse_req_init_context(fc, req);
req->waiting = 1;
req->background = for_background;
return req;
@@ -257,7 +257,7 @@ struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
if (!req)
req = get_reserved_req(fc, file);

- fuse_req_init_context(req);
+ fuse_req_init_context(fc, req);
req->waiting = 1;
req->background = 0;
return req;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index de1d84af9f7c..d74c75a057cd 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -886,7 +886,7 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
return err;
}

-static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
+static int fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
struct kstat *stat)
{
unsigned int blkbits;
@@ -905,8 +905,12 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
stat->ino = attr->ino;
stat->mode = (inode->i_mode & S_IFMT) | (attr->mode & 07777);
stat->nlink = attr->nlink;
- stat->uid = make_kuid(&init_user_ns, attr->uid);
- stat->gid = make_kgid(&init_user_ns, attr->gid);
+ stat->uid = make_kuid(fc->user_ns, attr->uid);
+ if (!uid_valid(stat->uid))
+ return -EOVERFLOW;
+ stat->gid = make_kgid(fc->user_ns, attr->gid);
+ if (!gid_valid(stat->gid))
+ return -EOVERFLOW;
stat->rdev = inode->i_rdev;
stat->atime.tv_sec = attr->atime;
stat->atime.tv_nsec = attr->atimensec;
@@ -923,6 +927,7 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
blkbits = inode->i_sb->s_blocksize_bits;

stat->blksize = 1 << blkbits;
+ return 0;
}

static int fuse_do_getattr(struct inode *inode, struct kstat *stat,
@@ -973,7 +978,8 @@ static int fuse_do_getattr(struct inode *inode, struct kstat *stat,
attr_timeout(&outarg),
attr_version);
if (stat)
- fuse_fillattr(inode, &outarg.attr, stat);
+ err = fuse_fillattr(inode, &outarg.attr,
+ stat);
}
}
return err;
@@ -1556,17 +1562,25 @@ static bool update_mtime(unsigned ivalid, bool trust_local_mtime)
return true;
}

-static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
- bool trust_local_cmtime)
+static int iattr_to_fattr(struct fuse_conn *fc, struct iattr *iattr,
+ struct fuse_setattr_in *arg, bool trust_local_cmtime)
{
unsigned ivalid = iattr->ia_valid;

if (ivalid & ATTR_MODE)
arg->valid |= FATTR_MODE, arg->mode = iattr->ia_mode;
- if (ivalid & ATTR_UID)
- arg->valid |= FATTR_UID, arg->uid = from_kuid(&init_user_ns, iattr->ia_uid);
- if (ivalid & ATTR_GID)
- arg->valid |= FATTR_GID, arg->gid = from_kgid(&init_user_ns, iattr->ia_gid);
+ if (ivalid & ATTR_UID) {
+ arg->valid |= FATTR_UID;
+ arg->uid = from_kuid(fc->user_ns, iattr->ia_uid);
+ if (arg->uid == (uid_t)-1)
+ return -EOVERFLOW;
+ }
+ if (ivalid & ATTR_GID) {
+ arg->valid |= FATTR_GID;
+ arg->gid = from_kgid(fc->user_ns, iattr->ia_gid);
+ if (arg->gid == (gid_t)-1)
+ return -EOVERFLOW;
+ }
if (ivalid & ATTR_SIZE)
arg->valid |= FATTR_SIZE, arg->size = iattr->ia_size;
if (ivalid & ATTR_ATIME) {
@@ -1588,6 +1602,7 @@ static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
arg->ctime = iattr->ia_ctime.tv_sec;
arg->ctimensec = iattr->ia_ctime.tv_nsec;
}
+ return 0;
}

/*
@@ -1741,7 +1756,11 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,

memset(&inarg, 0, sizeof(inarg));
memset(&outarg, 0, sizeof(outarg));
- iattr_to_fattr(attr, &inarg, trust_local_cmtime);
+ err = iattr_to_fattr(fc, attr, &inarg, trust_local_cmtime);
+ if (err) {
+ goto error;
+ }
+
if (file) {
struct fuse_file *ff = file->private_data;
inarg.valid |= FATTR_FH;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e8e47a6ab518..e7dbbb5d62b4 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -598,6 +598,9 @@ struct fuse_conn {

/** Read/write semaphore to hold when accessing sb. */
struct rw_semaphore killsb;
+
+ /** User namespace to communicate uids and gids to the fuse daemon */
+ struct user_namespace *user_ns;
};

static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 03246cd9d47a..894288f7ad67 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -20,6 +20,7 @@
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/exportfs.h>
+#include <linux/user_namespace.h>

MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -577,8 +578,8 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
struct super_block *sb = root->d_sb;
struct fuse_conn *fc = get_fuse_conn_super(sb);

- seq_printf(m, ",user_id=%u", from_kuid_munged(&init_user_ns, fc->user_id));
- seq_printf(m, ",group_id=%u", from_kgid_munged(&init_user_ns, fc->group_id));
+ seq_printf(m, ",user_id=%u", from_kuid_munged(fc->user_ns, fc->user_id));
+ seq_printf(m, ",group_id=%u", from_kgid_munged(fc->user_ns, fc->group_id));
if (fc->flags & FUSE_DEFAULT_PERMISSIONS)
seq_puts(m, ",default_permissions");
if (fc->flags & FUSE_ALLOW_OTHER)
@@ -616,6 +617,7 @@ void fuse_conn_init(struct fuse_conn *fc)
fc->initialized = 0;
fc->attr_version = 1;
get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
+ fc->user_ns = get_user_ns(current_user_ns());
}
EXPORT_SYMBOL_GPL(fuse_conn_init);

@@ -624,6 +626,8 @@ void fuse_conn_put(struct fuse_conn *fc)
if (atomic_dec_and_test(&fc->count)) {
if (fc->destroy_req)
fuse_request_free(fc->destroy_req);
+ put_user_ns(fc->user_ns);
+ fc->user_ns = NULL;
fc->release(fc);
}
}
@@ -1033,6 +1037,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_time_gran = 1;
sb->s_export_op = &fuse_export_operations;
+ sb->s_user_ns = get_user_ns(current_user_ns());

file = fget(d.fd);
err = -EINVAL;
@@ -1149,6 +1154,7 @@ static void fuse_kill_sb_anon(struct super_block *sb)
}

kill_anon_super(sb);
+ put_user_ns(sb->s_user_ns);
}

static struct file_system_type fuse_fs_type = {
--
1.9.1

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>From 9bdaa744858d296f361a92c8940c33f878aec169 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Thu, 4 Oct 2012 13:42:34 -0700
Subject: [PATCH 2/4] fuse: Teach fuse how to handle the pid namespace.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/fuse/dev.c | 2 +-
fs/fuse/file.c | 17 ++++++++++-------
fs/fuse/fuse_i.h | 3 +++
fs/fuse/inode.c | 4 ++++
4 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index e01f30c51b3c..448775701763 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -128,7 +128,7 @@ static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
{
req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
- req->in.h.pid = current->pid;
+ req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
}

static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 912061ac4baf..2d52801fa5dd 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2130,7 +2130,8 @@ static int fuse_direct_mmap(struct file *file, struct vm_area_struct *vma)
return generic_file_mmap(file, vma);
}

-static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
+static int convert_fuse_file_lock(struct fuse_conn *fc,
+ const struct fuse_file_lock *ffl,
struct file_lock *fl)
{
switch (ffl->type) {
@@ -2145,7 +2146,9 @@ static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,

fl->fl_start = ffl->start;
fl->fl_end = ffl->end;
- fl->fl_pid = ffl->pid;
+ rcu_read_lock();
+ fl->fl_pid = pid_vnr(find_pid_ns(ffl->pid, fc->pid_ns));
+ rcu_read_unlock();
break;

default:
@@ -2156,7 +2159,7 @@ static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
}

static void fuse_lk_fill(struct fuse_req *req, struct file *file,
- const struct file_lock *fl, int opcode, pid_t pid,
+ const struct file_lock *fl, int opcode, struct pid *pid,
int flock)
{
struct inode *inode = file_inode(file);
@@ -2169,7 +2172,7 @@ static void fuse_lk_fill(struct fuse_req *req, struct file *file,
arg->lk.start = fl->fl_start;
arg->lk.end = fl->fl_end;
arg->lk.type = fl->fl_type;
- arg->lk.pid = pid;
+ arg->lk.pid = pid_nr_ns(pid, fc->pid_ns);
if (flock)
arg->lk_flags |= FUSE_LK_FLOCK;
req->in.h.opcode = opcode;
@@ -2191,7 +2194,7 @@ static int fuse_getlk(struct file *file, struct file_lock *fl)
if (IS_ERR(req))
return PTR_ERR(req);

- fuse_lk_fill(req, file, fl, FUSE_GETLK, 0, 0);
+ fuse_lk_fill(req, file, fl, FUSE_GETLK, NULL, 0);
req->out.numargs = 1;
req->out.args[0].size = sizeof(outarg);
req->out.args[0].value = &outarg;
@@ -2199,7 +2202,7 @@ static int fuse_getlk(struct file *file, struct file_lock *fl)
err = req->out.h.error;
fuse_put_request(fc, req);
if (!err)
- err = convert_fuse_file_lock(&outarg.lk, fl);
+ err = convert_fuse_file_lock(fc, &outarg.lk, fl);

return err;
}
@@ -2210,7 +2213,7 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_req *req;
int opcode = (fl->fl_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
- pid_t pid = fl->fl_type != F_UNLCK ? current->tgid : 0;
+ struct pid *pid = fl->fl_type != F_UNLCK ? task_tgid(current) : NULL;
int err;

if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e7dbbb5d62b4..5d93f87e9960 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -601,6 +601,9 @@ struct fuse_conn {

/** User namespace to communicate uids and gids to the fuse daemon */
struct user_namespace *user_ns;
+
+ /** Pid namespace to communicate pids to the fuse daemon */
+ struct pid_namespace *pid_ns;
};

static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 894288f7ad67..5284d7fda269 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -21,6 +21,7 @@
#include <linux/sched.h>
#include <linux/exportfs.h>
#include <linux/user_namespace.h>
+#include <linux/pid_namespace.h>

MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -618,6 +619,7 @@ void fuse_conn_init(struct fuse_conn *fc)
fc->attr_version = 1;
get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
fc->user_ns = get_user_ns(current_user_ns());
+ fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
}
EXPORT_SYMBOL_GPL(fuse_conn_init);

@@ -628,6 +630,8 @@ void fuse_conn_put(struct fuse_conn *fc)
fuse_request_free(fc->destroy_req);
put_user_ns(fc->user_ns);
fc->user_ns = NULL;
+ put_pid_ns(fc->pid_ns);
+ fc->pid_ns = NULL;
fc->release(fc);
}
}
--
1.9.1

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>From 55226d169826abd110d9bc60a6b079f6be3f6a46 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Fri, 5 Oct 2012 10:18:28 -0700
Subject: [PATCH 3/4] userns: fuse unprivileged mount suport

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/fuse/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 5284d7fda269..75f5326868e0 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1164,7 +1164,7 @@ static void fuse_kill_sb_anon(struct super_block *sb)
static struct file_system_type fuse_fs_type = {
.owner = THIS_MODULE,
.name = "fuse",
- .fs_flags = FS_HAS_SUBTYPE,
+ .fs_flags = FS_HAS_SUBTYPE | FS_USERNS_MOUNT,
.mount = fuse_mount,
.kill_sb = fuse_kill_sb_anon,
};
--
1.9.1

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>From 6ae88ecfe4e8c8998478932ca225d1d9753b6c4b Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Fri, 5 Oct 2012 14:33:36 -0700
Subject: [PATCH 4/4] fuse: Only allow read/writing user xattrs

In the context of unprivileged mounts supporting anything except
xattrs with the "user." prefix seems foolish. Return -EOPNOSUPP
for all other types of xattrs.

Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/fuse/dir.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index d74c75a057cd..d84f5b819fab 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -13,6 +13,7 @@
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
+#include <linux/xattr.h>

static bool fuse_use_readdirplus(struct inode *dir, struct dir_context *ctx)
{
@@ -1868,6 +1869,9 @@ static int fuse_setxattr(struct dentry *entry, const char *name,
if (fc->no_setxattr)
return -EOPNOTSUPP;

+ if (strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) != 0)
+ return -EOPNOTSUPP;
+
req = fuse_get_req_nopages(fc);
if (IS_ERR(req))
return PTR_ERR(req);
@@ -1911,6 +1915,9 @@ static ssize_t fuse_getxattr(struct dentry *entry, const char *name,
if (fc->no_getxattr)
return -EOPNOTSUPP;

+ if (strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) != 0)
+ return -EOPNOTSUPP;
+
req = fuse_get_req_nopages(fc);
if (IS_ERR(req))
return PTR_ERR(req);
--
1.9.1