[PATCH] Generic VFS fallback for security xattrs

This patch modifies the VFS setxattr, getxattr, and listxattr code to fall
back to the security module for security xattrs if the filesystem does not
support xattrs natively.  This allows security modules to export the incore
inode security label information to userspace even if the filesystem does
not provide xattr storage, and eliminates the need to individually patch
various pseudo filesystem types to provide such access.  The patch removes
the existing xattr code from devpts and tmpfs as it is then no longer
needed.

The patch restructures the code flow slightly to reduce duplication between
the normal path and the fallback path, but this should only have one
user-visible side effect - a program may get -EACCES rather than
-EOPNOTSUPP if policy denied access but the filesystem didn't support the
operation anyway.  Note that the post_setxattr hook call is not needed in
the fallback case, as the inode_setsecurity hook call handles the incore
inode security state update directly.  In contrast, we do call fsnotify in
both cases.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 49 insertions, 31 deletions

diff --git a/fs/xattr.c b/fs/xattr.c
index 6acd5c63da91..dc8bc7624f26 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -51,20 +51,29 @@ setxattr(struct dentry *d, char __user *name, void __user *value,
                 }
         }
 
+        down(&d->d_inode->i_sem);
+        error = security_inode_setxattr(d, kname, kvalue, size, flags);
+        if (error)
+                goto out;
         error = -EOPNOTSUPP;
         if (d->d_inode->i_op && d->d_inode->i_op->setxattr) {
-                down(&d->d_inode->i_sem);
-                error = security_inode_setxattr(d, kname, kvalue, size, flags);
-                if (error)
-                        goto out;
-                error = d->d_inode->i_op->setxattr(d, kname, kvalue, size, flags);
+                error = d->d_inode->i_op->setxattr(d, kname, kvalue,
+                                                   size, flags);
                 if (!error) {
                         fsnotify_xattr(d);
-                        security_inode_post_setxattr(d, kname, kvalue, size, flags);
+                        security_inode_post_setxattr(d, kname, kvalue,
+                                                     size, flags);
                 }
-out:
-                up(&d->d_inode->i_sem);
+        } else if (!strncmp(kname, XATTR_SECURITY_PREFIX,
+                            sizeof XATTR_SECURITY_PREFIX - 1)) {
+                const char *suffix = kname + sizeof XATTR_SECURITY_PREFIX - 1;
+                error = security_inode_setsecurity(d->d_inode, suffix, kvalue,
+                                                   size, flags);
+                if (!error)
+                        fsnotify_xattr(d);
         }
+out:
+        up(&d->d_inode->i_sem);
         if (kvalue)
                 kfree(kvalue);
         return error;
@@ -139,20 +148,25 @@ getxattr(struct dentry *d, char __user *name, void __user *value, size_t size)
                         return -ENOMEM;
         }
 
+        error = security_inode_getxattr(d, kname);
+        if (error)
+                goto out;
         error = -EOPNOTSUPP;
-        if (d->d_inode->i_op && d->d_inode->i_op->getxattr) {
-                error = security_inode_getxattr(d, kname);
-                if (error)
-                        goto out;
+        if (d->d_inode->i_op && d->d_inode->i_op->getxattr)
                 error = d->d_inode->i_op->getxattr(d, kname, kvalue, size);
-                if (error > 0) {
-                        if (size && copy_to_user(value, kvalue, error))
-                                error = -EFAULT;
-                } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
-                        /* The file system tried to returned a value bigger
-                           than XATTR_SIZE_MAX bytes. Not possible. */
-                        error = -E2BIG;
-                }
+        else if (!strncmp(kname, XATTR_SECURITY_PREFIX,
+                          sizeof XATTR_SECURITY_PREFIX - 1)) {
+                const char *suffix = kname + sizeof XATTR_SECURITY_PREFIX - 1;
+                error = security_inode_getsecurity(d->d_inode, suffix, kvalue,
+                                                   size);
+        }
+        if (error > 0) {
+                if (size && copy_to_user(value, kvalue, error))
+                        error = -EFAULT;
+        } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
+                /* The file system tried to returned a value bigger
+                   than XATTR_SIZE_MAX bytes. Not possible. */
+                error = -E2BIG;
         }
 out:
         if (kvalue)
@@ -221,20 +235,24 @@ listxattr(struct dentry *d, char __user *list, size_t size)
                         return -ENOMEM;
         }
 
+        error = security_inode_listxattr(d);
+        if (error)
+                goto out;
         error = -EOPNOTSUPP;
         if (d->d_inode->i_op && d->d_inode->i_op->listxattr) {
-                error = security_inode_listxattr(d);
-                if (error)
-                        goto out;
                 error = d->d_inode->i_op->listxattr(d, klist, size);
-                if (error > 0) {
-                        if (size && copy_to_user(list, klist, error))
-                                error = -EFAULT;
-                } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
-                        /* The file system tried to returned a list bigger
-                           than XATTR_LIST_MAX bytes. Not possible. */
-                        error = -E2BIG;
-                }
+        } else {
+                error = security_inode_listsecurity(d->d_inode, klist, size);
+                if (size && error >= size)
+                        error = -ERANGE;
+        }
+        if (error > 0) {
+                if (size && copy_to_user(list, klist, error))
+                        error = -EFAULT;
+        } else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
+                /* The file system tried to returned a list bigger
+                   than XATTR_LIST_MAX bytes. Not possible. */
+                error = -E2BIG;
         }
 out:
         if (klist)