Messages in this thread | | | Date | Sat, 5 Mar 2011 12:21:40 +0100 | From | Bruno Prémont <> | Subject | Re: [PATCH] tmpfs: implement security.capability xattrs |
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On Wed, 02 March 2011 Eric Paris <eparis@parisplace.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@parisplace.org> wrote: > > Bueller? Bueller? Any thoughts? Any problems? > > > > On Tue, Jan 11, 2011 at 4:07 PM, Eric Paris <eparis@redhat.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@redhat.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 = { > >> -- 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/
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