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Message-ID: <20110305122140.010ef7f8@neptune.home>
Date: Sat, 5 Mar 2011 12:21:40 +0100
From: Bruno Prémont <bonbons@...ux-vserver.org>
To: Eric Paris <eparis@...isplace.org>
Cc: Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, hughd@...gle.com,
linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] tmpfs: implement security.capability xattrs
On Wed, 02 March 2011 Eric Paris <eparis@...isplace.org> wrote:
> I know there exist thoughts on this patch somewhere on the internets.
> Let 'em rip! I can handle it!
Hi Eric,
I have not read the code behind CONFIG_TMPFS_POSIX_ACL in depth but it
does seem to already use some XATTR support for making posix acls
available.
Your patch looks like not touching/using that support, maybe there is
already some of your work previously done (according to comment in
mm/shmem.c offered for free by VFS).
Did I miss something essential?
Regards,
Bruno
> -Eric
>
> On Thu, Feb 17, 2011 at 4:27 PM, Eric Paris <eparis@...isplace.org> wrote:
> > Bueller? Bueller? Any thoughts? Any problems?
> >
> > On Tue, Jan 11, 2011 at 4:07 PM, Eric Paris <eparis@...hat.com> wrote:
> >> This patch implements security.capability xattrs for tmpfs filesystems. The
> >> feodra project, while trying to replace suid apps with file capabilities,
> >> realized that tmpfs, which is used on my build systems, does not support file
> >> capabilities and thus cannot be used to build packages which use file
> >> capabilities. The patch only implements security.capability but there is no
> >> reason it could not be easily expanded to support *.* xattrs as most of the
> >> work is already done. I don't know what other xattrs are in use in the world
> >> or if they necessarily make sense on tmpfs so I didn't make this
> >> implementation completely generic.
> >>
> >> The basic implementation is that I attach a
> >> struct shmem_xattr {
> >> struct list_head list; /* anchored by shmem_inode_info->xattr_list */
> >> char *name;
> >> size_t size;
> >> char value[0];
> >> };
> >> Into the struct shmem_inode_info for each xattr that is set. Since I only
> >> allow security.capability obviously this list is only every 0 or 1 entry long.
> >> I could have been a little simpler, but then the next person having to
> >> implement an xattr would have to redo everything I did instead of me just
> >> doing 90% of their work :)
> >>
> >> Signed-off-by: Eric Paris <eparis@...hat.com>
> >> ---
> >>
> >> include/linux/shmem_fs.h | 8 +++
> >> mm/shmem.c | 112 ++++++++++++++++++++++++++++++++++++++++++++--
> >> 2 files changed, 116 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> >> index 399be5a..6f2ebb8 100644
> >> --- a/include/linux/shmem_fs.h
> >> +++ b/include/linux/shmem_fs.h
> >> @@ -9,6 +9,13 @@
> >>
> >> #define SHMEM_NR_DIRECT 16
> >>
> >> +struct shmem_xattr {
> >> + struct list_head list; /* anchored by shmem_inode_info->xattr_list */
> >> + char *name;
> >> + size_t size;
> >> + char value[0];
> >> +};
> >> +
> >> struct shmem_inode_info {
> >> spinlock_t lock;
> >> unsigned long flags;
> >> @@ -19,6 +26,7 @@ struct shmem_inode_info {
> >> struct page *i_indirect; /* top indirect blocks page */
> >> swp_entry_t i_direct[SHMEM_NR_DIRECT]; /* first blocks */
> >> struct list_head swaplist; /* chain of maybes on swap */
> >> + struct list_head xattr_list; /* list of shmem_xattr */
> >> struct inode vfs_inode;
> >> };
> >>
> >> diff --git a/mm/shmem.c b/mm/shmem.c
> >> index 86cd21d..d2bacd6 100644
> >> --- a/mm/shmem.c
> >> +++ b/mm/shmem.c
> >> @@ -822,6 +822,7 @@ static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
> >> static void shmem_evict_inode(struct inode *inode)
> >> {
> >> struct shmem_inode_info *info = SHMEM_I(inode);
> >> + struct shmem_xattr *xattr, *nxattr;
> >>
> >> if (inode->i_mapping->a_ops == &shmem_aops) {
> >> truncate_inode_pages(inode->i_mapping, 0);
> >> @@ -834,6 +835,9 @@ static void shmem_evict_inode(struct inode *inode)
> >> mutex_unlock(&shmem_swaplist_mutex);
> >> }
> >> }
> >> +
> >> + list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, list)
> >> + kfree(xattr);
> >> BUG_ON(inode->i_blocks);
> >> shmem_free_inode(inode->i_sb);
> >> end_writeback(inode);
> >> @@ -1597,6 +1601,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
> >> spin_lock_init(&info->lock);
> >> info->flags = flags & VM_NORESERVE;
> >> INIT_LIST_HEAD(&info->swaplist);
> >> + INIT_LIST_HEAD(&info->xattr_list);
> >> cache_no_acl(inode);
> >>
> >> switch (mode & S_IFMT) {
> >> @@ -2071,24 +2076,123 @@ static size_t shmem_xattr_security_list(struct dentry *dentry, char *list,
> >> size_t list_len, const char *name,
> >> size_t name_len, int handler_flags)
> >> {
> >> - return security_inode_listsecurity(dentry->d_inode, list, list_len);
> >> + struct shmem_xattr *xattr;
> >> + struct shmem_inode_info *shmem_i;
> >> + size_t used;
> >> + char *buf = NULL;
> >> +
> >> + used = security_inode_listsecurity(dentry->d_inode, list, list_len);
> >> +
> >> + shmem_i = SHMEM_I(dentry->d_inode);
> >> + if (list)
> >> + buf = list + used;
> >> +
> >> + spin_lock(&dentry->d_inode->i_lock);
> >> + list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> >> + size_t len = XATTR_SECURITY_PREFIX_LEN;
> >> + len += strlen(xattr->name) + 1;
> >> + if (list_len - (used + len) >= 0 && buf) {
> >> + strncpy(buf, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN);
> >> + buf += XATTR_SECURITY_PREFIX_LEN;
> >> + strncpy(buf, xattr->name, strlen(xattr->name) + 1);
> >> + buf += strlen(xattr->name) + 1;
> >> + }
> >> + used += len;
> >> + }
> >> + spin_unlock(&dentry->d_inode->i_lock);
> >> +
> >> + return used;
> >> }
> >>
> >> static int shmem_xattr_security_get(struct dentry *dentry, const char *name,
> >> void *buffer, size_t size, int handler_flags)
> >> {
> >> + struct shmem_inode_info *shmem_i;
> >> + struct shmem_xattr *xattr;
> >> + int ret;
> >> +
> >> if (strcmp(name, "") == 0)
> >> return -EINVAL;
> >> - return xattr_getsecurity(dentry->d_inode, name, buffer, size);
> >> +
> >> + ret = xattr_getsecurity(dentry->d_inode, name, buffer, size);
> >> + if (ret != -EOPNOTSUPP)
> >> + return ret;
> >> +
> >> + /* if we make this generic this needs to go... */
> >> + if (strcmp(name, XATTR_CAPS_SUFFIX))
> >> + return -EOPNOTSUPP;
> >> +
> >> + ret = -ENODATA;
> >> + shmem_i = SHMEM_I(dentry->d_inode);
> >> +
> >> + spin_lock(&dentry->d_inode->i_lock);
> >> + list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> >> + if (!strcmp(name, xattr->name)) {
> >> + ret = xattr->size;
> >> + if (buffer) {
> >> + if (size < xattr->size)
> >> + ret = -ERANGE;
> >> + else
> >> + memcpy(buffer, xattr->value, xattr->size);
> >> + }
> >> + break;
> >> + }
> >> + }
> >> + spin_unlock(&dentry->d_inode->i_lock);
> >> + return ret;
> >> }
> >>
> >> static int shmem_xattr_security_set(struct dentry *dentry, const char *name,
> >> const void *value, size_t size, int flags, int handler_flags)
> >> {
> >> + int ret;
> >> + struct inode *inode = dentry->d_inode;
> >> + struct shmem_inode_info *shmem_i = SHMEM_I(inode);
> >> + struct shmem_xattr *xattr;
> >> + struct shmem_xattr *new_xattr;
> >> + size_t len;
> >> +
> >> if (strcmp(name, "") == 0)
> >> return -EINVAL;
> >> - return security_inode_setsecurity(dentry->d_inode, name, value,
> >> - size, flags);
> >> + ret = security_inode_setsecurity(inode, name, value, size, flags);
> >> + if (ret != -EOPNOTSUPP)
> >> + return ret;
> >> +
> >> + /*
> >> + * We only store fcaps for now, but this could be a lot more generic.
> >> + * We could hold the prefix as well as the suffix in the xattr struct
> >> + * We would also need to hold a copy of the suffix rather than a
> >> + * pointer to XATTR_CAPS_SUFFIX
> >> + */
> >> + if (strcmp(name, XATTR_CAPS_SUFFIX))
> >> + return -EOPNOTSUPP;
> >> +
> >> + /* wrap around? */
> >> + len = sizeof(*new_xattr) + size;
> >> + if (len <= sizeof(*new_xattr))
> >> + return -ENOMEM;
> >> +
> >> + new_xattr = kmalloc(GFP_NOFS, len);
> >> + if (!new_xattr)
> >> + return -ENOMEM;
> >> +
> >> + new_xattr->name = XATTR_CAPS_SUFFIX;
> >> + new_xattr->size = size;
> >> + memcpy(new_xattr->value, value, size);
> >> +
> >> + spin_lock(&inode->i_lock);
> >> + list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> >> + if (!strcmp(name, xattr->name)) {
> >> + list_replace(&xattr->list, &new_xattr->list);
> >> + goto out;
> >> + }
> >> + }
> >> + list_add(&new_xattr->list, &shmem_i->xattr_list);
> >> + xattr = NULL;
> >> +out:
> >> + spin_unlock(&inode->i_lock);
> >> + kfree(xattr);
> >> + return 0;
> >> }
> >>
> >> static const struct xattr_handler shmem_xattr_security_handler = {
> >>
--
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