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References: <20110111210710.32348.1642.stgit@paris.rdu.redhat.com>
Date: Thu, 17 Feb 2011 16:27:28 -0500
Message-ID: <AANLkTi=wyaLP6gFmNxajp+HtYu3B9_KGf2o4BnYA+rwy@mail.gmail.com>
Subject: Re: [PATCH] tmpfs: implement security.capability xattrs
From: Eric Paris <eparis@parisplace.org>
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Sender: owner-linux-mm@kvack.org
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To: Eric Paris <eparis@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, hughd@google.com, linux-fsdevel@vger.kernel.org

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. =
=A0The
> 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. =A0The patch only implements security.capability but there =
is no
> reason it could not be easily expanded to support *.* xattrs as most of t=
he
> work is already done. =A0I 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 {
> =A0 =A0 =A0 =A0struct list_head list; /* anchored by shmem_inode_info->xa=
ttr_list */
> =A0 =A0 =A0 =A0char *name;
> =A0 =A0 =A0 =A0size_t size;
> =A0 =A0 =A0 =A0char value[0];
> };
> Into the struct shmem_inode_info for each xattr that is set. =A0Since I o=
nly
> 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 =A0:)
>
> Signed-off-by: Eric Paris <eparis@redhat.com>
> ---
>
> =A0include/linux/shmem_fs.h | =A0 =A08 +++
> =A0mm/shmem.c =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0112 ++++++++++++++++++++++=
++++++++++++++++++++++--
> =A02 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 @@
>
> =A0#define SHMEM_NR_DIRECT 16
>
> +struct shmem_xattr {
> + =A0 =A0 =A0 struct list_head list; /* anchored by shmem_inode_info->xat=
tr_list */
> + =A0 =A0 =A0 char *name;
> + =A0 =A0 =A0 size_t size;
> + =A0 =A0 =A0 char value[0];
> +};
> +
> =A0struct shmem_inode_info {
> =A0 =A0 =A0 =A0spinlock_t =A0 =A0 =A0 =A0 =A0 =A0 =A0lock;
> =A0 =A0 =A0 =A0unsigned long =A0 =A0 =A0 =A0 =A0 flags;
> @@ -19,6 +26,7 @@ struct shmem_inode_info {
> =A0 =A0 =A0 =A0struct page =A0 =A0 =A0 =A0 =A0 =A0 *i_indirect; =A0 =A0/*=
 top indirect blocks page */
> =A0 =A0 =A0 =A0swp_entry_t =A0 =A0 =A0 =A0 =A0 =A0 i_direct[SHMEM_NR_DIRE=
CT]; /* first blocks */
> =A0 =A0 =A0 =A0struct list_head =A0 =A0 =A0 =A0swaplist; =A0 =A0 =A0 /* c=
hain of maybes on swap */
> + =A0 =A0 =A0 struct list_head =A0 =A0 =A0 =A0xattr_list; =A0 =A0 /* list=
 of shmem_xattr */
> =A0 =A0 =A0 =A0struct inode =A0 =A0 =A0 =A0 =A0 =A0vfs_inode;
> =A0};
>
> 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)
> =A0static void shmem_evict_inode(struct inode *inode)
> =A0{
> =A0 =A0 =A0 =A0struct shmem_inode_info *info =3D SHMEM_I(inode);
> + =A0 =A0 =A0 struct shmem_xattr *xattr, *nxattr;
>
> =A0 =A0 =A0 =A0if (inode->i_mapping->a_ops =3D=3D &shmem_aops) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0truncate_inode_pages(inode->i_mapping, 0);
> @@ -834,6 +835,9 @@ static void shmem_evict_inode(struct inode *inode)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0mutex_unlock(&shmem_swapli=
st_mutex);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0}
> +
> + =A0 =A0 =A0 list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, =
list)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 kfree(xattr);
> =A0 =A0 =A0 =A0BUG_ON(inode->i_blocks);
> =A0 =A0 =A0 =A0shmem_free_inode(inode->i_sb);
> =A0 =A0 =A0 =A0end_writeback(inode);
> @@ -1597,6 +1601,7 @@ static struct inode *shmem_get_inode(struct super_b=
lock *sb, const struct inode
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0spin_lock_init(&info->lock);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0info->flags =3D flags & VM_NORESERVE;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0INIT_LIST_HEAD(&info->swaplist);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 INIT_LIST_HEAD(&info->xattr_list);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0cache_no_acl(inode);
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0switch (mode & S_IFMT) {
> @@ -2071,24 +2076,123 @@ static size_t shmem_xattr_security_list(struct d=
entry *dentry, char *list,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0size_t list_len, const char *name,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0size_t name_len, int handler_flags)
> =A0{
> - =A0 =A0 =A0 return security_inode_listsecurity(dentry->d_inode, list, l=
ist_len);
> + =A0 =A0 =A0 struct shmem_xattr *xattr;
> + =A0 =A0 =A0 struct shmem_inode_info *shmem_i;
> + =A0 =A0 =A0 size_t used;
> + =A0 =A0 =A0 char *buf =3D NULL;
> +
> + =A0 =A0 =A0 used =3D security_inode_listsecurity(dentry->d_inode, list,=
 list_len);
> +
> + =A0 =A0 =A0 shmem_i =3D SHMEM_I(dentry->d_inode);
> + =A0 =A0 =A0 if (list)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 buf =3D list + used;
> +
> + =A0 =A0 =A0 spin_lock(&dentry->d_inode->i_lock);
> + =A0 =A0 =A0 list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 size_t len =3D XATTR_SECURITY_PREFIX_LEN;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 len +=3D strlen(xattr->name) + 1;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (list_len - (used + len) >=3D 0 && buf) =
{
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 strncpy(buf, XATTR_SECURITY=
_PREFIX, XATTR_SECURITY_PREFIX_LEN);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 buf +=3D XATTR_SECURITY_PRE=
FIX_LEN;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 strncpy(buf, xattr->name, s=
trlen(xattr->name) + 1);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 buf +=3D strlen(xattr->name=
) + 1;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 used +=3D len;
> + =A0 =A0 =A0 }
> + =A0 =A0 =A0 spin_unlock(&dentry->d_inode->i_lock);
> +
> + =A0 =A0 =A0 return used;
> =A0}
>
> =A0static int shmem_xattr_security_get(struct dentry *dentry, const char =
*name,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0void *buffer, size_t size, int handler_fla=
gs)
> =A0{
> + =A0 =A0 =A0 struct shmem_inode_info *shmem_i;
> + =A0 =A0 =A0 struct shmem_xattr *xattr;
> + =A0 =A0 =A0 int ret;
> +
> =A0 =A0 =A0 =A0if (strcmp(name, "") =3D=3D 0)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return -EINVAL;
> - =A0 =A0 =A0 return xattr_getsecurity(dentry->d_inode, name, buffer, siz=
e);
> +
> + =A0 =A0 =A0 ret =3D xattr_getsecurity(dentry->d_inode, name, buffer, si=
ze);
> + =A0 =A0 =A0 if (ret !=3D -EOPNOTSUPP)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return ret;
> +
> + =A0 =A0 =A0 /* if we make this generic this needs to go... */
> + =A0 =A0 =A0 if (strcmp(name, XATTR_CAPS_SUFFIX))
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EOPNOTSUPP;
> +
> + =A0 =A0 =A0 ret =3D -ENODATA;
> + =A0 =A0 =A0 shmem_i =3D SHMEM_I(dentry->d_inode);
> +
> + =A0 =A0 =A0 spin_lock(&dentry->d_inode->i_lock);
> + =A0 =A0 =A0 list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!strcmp(name, xattr->name)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D xattr->size;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (buffer) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (size < =
xattr->size)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 ret =3D -ERANGE;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 else
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 memcpy(buffer, xattr->value, xattr->size);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 }
> + =A0 =A0 =A0 spin_unlock(&dentry->d_inode->i_lock);
> + =A0 =A0 =A0 return ret;
> =A0}
>
> =A0static int shmem_xattr_security_set(struct dentry *dentry, const char =
*name,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0const void *value, size_t size, int flags,=
 int handler_flags)
> =A0{
> + =A0 =A0 =A0 int ret;
> + =A0 =A0 =A0 struct inode *inode =3D dentry->d_inode;
> + =A0 =A0 =A0 struct shmem_inode_info *shmem_i =3D SHMEM_I(inode);
> + =A0 =A0 =A0 struct shmem_xattr *xattr;
> + =A0 =A0 =A0 struct shmem_xattr *new_xattr;
> + =A0 =A0 =A0 size_t len;
> +
> =A0 =A0 =A0 =A0if (strcmp(name, "") =3D=3D 0)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return -EINVAL;
> - =A0 =A0 =A0 return security_inode_setsecurity(dentry->d_inode, name, va=
lue,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 size, flags);
> + =A0 =A0 =A0 ret =3D security_inode_setsecurity(inode, name, value, size=
, flags);
> + =A0 =A0 =A0 if (ret !=3D -EOPNOTSUPP)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return ret;
> +
> + =A0 =A0 =A0 /*
> + =A0 =A0 =A0 =A0* We only store fcaps for now, but this could be a lot m=
ore generic.
> + =A0 =A0 =A0 =A0* We could hold the prefix as well as the suffix in the =
xattr struct
> + =A0 =A0 =A0 =A0* We would also need to hold a copy of the suffix rather=
 than a
> + =A0 =A0 =A0 =A0* pointer to XATTR_CAPS_SUFFIX
> + =A0 =A0 =A0 =A0*/
> + =A0 =A0 =A0 if (strcmp(name, XATTR_CAPS_SUFFIX))
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EOPNOTSUPP;
> +
> + =A0 =A0 =A0 /* wrap around? */
> + =A0 =A0 =A0 len =3D sizeof(*new_xattr) + size;
> + =A0 =A0 =A0 if (len <=3D sizeof(*new_xattr))
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -ENOMEM;
> +
> + =A0 =A0 =A0 new_xattr =3D kmalloc(GFP_NOFS, len);
> + =A0 =A0 =A0 if (!new_xattr)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -ENOMEM;
> +
> + =A0 =A0 =A0 new_xattr->name =3D XATTR_CAPS_SUFFIX;
> + =A0 =A0 =A0 new_xattr->size =3D size;
> + =A0 =A0 =A0 memcpy(new_xattr->value, value, size);
> +
> + =A0 =A0 =A0 spin_lock(&inode->i_lock);
> + =A0 =A0 =A0 list_for_each_entry(xattr, &shmem_i->xattr_list, list) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!strcmp(name, xattr->name)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 list_replace(&xattr->list, =
&new_xattr->list);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 }
> + =A0 =A0 =A0 list_add(&new_xattr->list, &shmem_i->xattr_list);
> + =A0 =A0 =A0 xattr =3D NULL;
> +out:
> + =A0 =A0 =A0 spin_unlock(&inode->i_lock);
> + =A0 =A0 =A0 kfree(xattr);
> + =A0 =A0 =A0 return 0;
> =A0}
>
> =A0static const struct xattr_handler shmem_xattr_security_handler =3D {
>
> --
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