Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752625Ab1CELWk (ORCPT ); Sat, 5 Mar 2011 06:22:40 -0500 Received: from legolas.restena.lu ([158.64.1.34]:51655 "EHLO legolas.restena.lu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751553Ab1CELWj convert rfc822-to-8bit (ORCPT ); Sat, 5 Mar 2011 06:22:39 -0500 Date: Sat, 5 Mar 2011 12:21:40 +0100 From: Bruno =?UTF-8?B?UHLDqW1vbnQ=?= To: Eric Paris Cc: Eric Paris , linux-kernel@vger.kernel.org, linux-mm@kvack.org, hughd@google.com, linux-fsdevel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] tmpfs: implement security.capability xattrs Message-ID: <20110305122140.010ef7f8@neptune.home> In-Reply-To: References: <20110111210710.32348.1642.stgit@paris.rdu.redhat.com> X-Mailer: Claws Mail 3.7.8 (GTK+ 2.22.1; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10987 Lines: 245 On Wed, 02 March 2011 Eric Paris 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 wrote: > > Bueller?  Bueller?  Any thoughts?  Any problems? > > > > On Tue, Jan 11, 2011 at 4:07 PM, Eric Paris 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 > >> --- > >> > >>  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 = { > >> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/