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SubjectRe: [PATCH] tmpfs: security xattr setting on inode creation
Thanks a lot for doing this, Jarkko: I knew nothing about it.
And thank you James for reviewing, I felt much happier seeing that.

I did fiddle around with it slightly, to reduce the added textsize,
and eliminate it when CONFIG_TMPFS_XATTR is off. Please, Jarkko
and James, complain bitterly if I've messed up the good work.

[PATCH] tmpfs: security xattr setting on inode creation

From: Jarkko Sakkinen <jarkko.sakkinen@intel.com>

Adds to generic xattr support introduced in Linux 3.0 by
implementing initxattrs callback. This enables consulting
of security attributes from LSM and EVM when inode is created.

[hughd: moved under CONFIG_TMPFS_XATTR, with memcpy in shmem_xattr_alloc]

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/shmem.c | 88 +++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 72 insertions(+), 16 deletions(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1178,6 +1178,12 @@ static struct inode *shmem_get_inode(str
static const struct inode_operations shmem_symlink_inode_operations;
static const struct inode_operations shmem_short_symlink_operations;

+#ifdef CONFIG_TMPFS_XATTR
+static int shmem_initxattrs(struct inode *, const struct xattr *, void *);
+#else
+#define shmem_initxattrs NULL
+#endif
+
static int
shmem_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
@@ -1490,7 +1496,7 @@ shmem_mknod(struct inode *dir, struct de
if (inode) {
error = security_inode_init_security(inode, dir,
&dentry->d_name,
- NULL, NULL);
+ shmem_initxattrs, NULL);
if (error) {
if (error != -EOPNOTSUPP) {
iput(inode);
@@ -1630,7 +1636,7 @@ static int shmem_symlink(struct inode *d
return -ENOSPC;

error = security_inode_init_security(inode, dir, &dentry->d_name,
- NULL, NULL);
+ shmem_initxattrs, NULL);
if (error) {
if (error != -EOPNOTSUPP) {
iput(inode);
@@ -1704,6 +1710,66 @@ static void shmem_put_link(struct dentry
* filesystem level, though.
*/

+/*
+ * Allocate new xattr and copy in the value; but leave the name to callers.
+ */
+static struct shmem_xattr *shmem_xattr_alloc(const void *value, size_t size)
+{
+ struct shmem_xattr *new_xattr;
+ size_t len;
+
+ /* wrap around? */
+ len = sizeof(*new_xattr) + size;
+ if (len <= sizeof(*new_xattr))
+ return NULL;
+
+ new_xattr = kmalloc(len, GFP_KERNEL);
+ if (!new_xattr)
+ return NULL;
+
+ new_xattr->size = size;
+ memcpy(new_xattr->value, value, size);
+ return new_xattr;
+}
+
+/*
+ * Callback for security_inode_init_security() for acquiring xattrs.
+ */
+static int shmem_initxattrs(struct inode *inode,
+ const struct xattr *xattr_array,
+ void *fs_info)
+{
+ struct shmem_inode_info *info = SHMEM_I(inode);
+ const struct xattr *xattr;
+ struct shmem_xattr *new_xattr;
+ size_t len;
+
+ for (xattr = xattr_array; xattr->name != NULL; xattr++) {
+ new_xattr = shmem_xattr_alloc(xattr->value, xattr->value_len);
+ if (!new_xattr)
+ return -ENOMEM;
+
+ len = strlen(xattr->name) + 1;
+ new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
+ GFP_KERNEL);
+ if (!new_xattr->name) {
+ kfree(new_xattr);
+ return -ENOMEM;
+ }
+
+ memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
+ XATTR_SECURITY_PREFIX_LEN);
+ memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
+ xattr->name, len);
+
+ spin_lock(&info->lock);
+ list_add(&new_xattr->list, &info->xattr_list);
+ spin_unlock(&info->lock);
+ }
+
+ return 0;
+}
+
static int shmem_xattr_get(struct dentry *dentry, const char *name,
void *buffer, size_t size)
{
@@ -1731,24 +1797,17 @@ static int shmem_xattr_get(struct dentry
return ret;
}

-static int shmem_xattr_set(struct dentry *dentry, const char *name,
+static int shmem_xattr_set(struct inode *inode, const char *name,
const void *value, size_t size, int flags)
{
- struct inode *inode = dentry->d_inode;
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_xattr *xattr;
struct shmem_xattr *new_xattr = NULL;
- size_t len;
int err = 0;

/* value == NULL means remove */
if (value) {
- /* wrap around? */
- len = sizeof(*new_xattr) + size;
- if (len <= sizeof(*new_xattr))
- return -ENOMEM;
-
- new_xattr = kmalloc(len, GFP_KERNEL);
+ new_xattr = shmem_xattr_alloc(value, size);
if (!new_xattr)
return -ENOMEM;

@@ -1757,9 +1816,6 @@ static int shmem_xattr_set(struct dentry
kfree(new_xattr);
return -ENOMEM;
}
-
- new_xattr->size = size;
- memcpy(new_xattr->value, value, size);
}

spin_lock(&info->lock);
@@ -1858,7 +1914,7 @@ static int shmem_setxattr(struct dentry
if (size == 0)
value = ""; /* empty EA, do not remove */

- return shmem_xattr_set(dentry, name, value, size, flags);
+ return shmem_xattr_set(dentry->d_inode, name, value, size, flags);

}

@@ -1878,7 +1934,7 @@ static int shmem_removexattr(struct dent
if (err)
return err;

- return shmem_xattr_set(dentry, name, NULL, 0, XATTR_REPLACE);
+ return shmem_xattr_set(dentry->d_inode, name, NULL, 0, XATTR_REPLACE);
}

static bool xattr_is_trusted(const char *name)

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