VFS/Security: Rework inode_getsecurity and callers to return resulting buffer

This patch modifies the interface to inode_getsecurity to have the function
return a buffer containing the security blob and its length via parameters
instead of relying on the calling function to give it an appropriately sized
buffer.

Security blobs obtained with this function should be freed using the
release_secctx LSM hook.  This alleviates the problem of the caller having to
guess a length and preallocate a buffer for this function allowing it to be
used elsewhere for Labeled NFS.

The patch also removed the unused err parameter.  The conversion is similar to
the one performed by Al Viro for the security_getprocattr hook.

Signed-off-by: David P. Quigley <dpquigl@tycho.nsa.gov>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Chris Wright <chrisw@sous-sol.org>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/xattr.c b/fs/xattr.c
index 6645b7313b3372a0a490bdc9b382f81fc8ace71c..1858552a6a1a0c6af76afb92316507c7d2d352eb 100644 (file)
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -104,6 +104,33 @@ out:
 }
 EXPORT_SYMBOL_GPL(vfs_setxattr);
 
+ssize_t
+xattr_getsecurity(struct inode *inode, const char *name, void *value,
+                       size_t size)
+{
+       void *buffer = NULL;
+       ssize_t len;
+
+       if (!value || !size) {
+               len = security_inode_getsecurity(inode, name, &buffer, false);
+               goto out_noalloc;
+       }
+
+       len = security_inode_getsecurity(inode, name, &buffer, true);
+       if (len < 0)
+               return len;
+       if (size < len) {
+               len = -ERANGE;
+               goto out;
+       }
+       memcpy(value, buffer, len);
+out:
+       security_release_secctx(buffer, len);
+out_noalloc:
+       return len;
+}
+EXPORT_SYMBOL_GPL(xattr_getsecurity);
+
 ssize_t
 vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
 {
@@ -126,8 +153,7 @@ vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
        if (!strncmp(name, XATTR_SECURITY_PREFIX,
                                XATTR_SECURITY_PREFIX_LEN)) {
                const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
-               int ret = security_inode_getsecurity(inode, suffix, value,
-                                                    size, error);
+               int ret = xattr_getsecurity(inode, suffix, value, size);
                /*
                 * Only overwrite the return value if a security module
                 * is actually active.

diff --git a/include/linux/security.h b/include/linux/security.h
index d24974262dc62a9376e6c6ffd1a4e7f42ca0196a..9d289e726fd88131fba5d10628e5cedf71135481 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -423,15 +423,12 @@ struct request_sock;
  *     identified by @name for @dentry.
  *     Return 0 if permission is granted.
  * @inode_getsecurity:
- *     Copy the extended attribute representation of the security label 
- *     associated with @name for @inode into @buffer.  @buffer may be
- *     NULL to request the size of the buffer required.  @size indicates
- *     the size of @buffer in bytes.  Note that @name is the remainder
- *     of the attribute name after the security. prefix has been removed.
- *     @err is the return value from the preceding fs getxattr call,
- *     and can be used by the security module to determine whether it
- *     should try and canonicalize the attribute value.
- *     Return number of bytes used/required on success.
+ *     Retrieve a copy of the extended attribute representation of the
+ *     security label associated with @name for @inode via @buffer.  Note that
+ *     @name is the remainder of the attribute name after the security prefix
+ *     has been removed. @alloc is used to specify of the call should return a
+ *     value via the buffer or just the value length Return size of buffer on
+ *     success.
  * @inode_setsecurity:
  *     Set the security label associated with @name for @inode from the
  *     extended attribute value @value.  @size indicates the size of the
@@ -1304,7 +1301,7 @@ struct security_operations {
        int (*inode_removexattr) (struct dentry *dentry, char *name);
        int (*inode_need_killpriv) (struct dentry *dentry);
        int (*inode_killpriv) (struct dentry *dentry);
-       int (*inode_getsecurity)(const struct inode *inode, const char *name, void *buffer, size_t size, int err);
+       int (*inode_getsecurity)(const struct inode *inode, const char *name, void **buffer, bool alloc);
        int (*inode_setsecurity)(struct inode *inode, const char *name, const void *value, size_t size, int flags);
        int (*inode_listsecurity)(struct inode *inode, char *buffer, size_t buffer_size);
 
@@ -1565,7 +1562,7 @@ int security_inode_listxattr(struct dentry *dentry);
 int security_inode_removexattr(struct dentry *dentry, char *name);
 int security_inode_need_killpriv(struct dentry *dentry);
 int security_inode_killpriv(struct dentry *dentry);
-int security_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err);
+int security_inode_getsecurity(const struct inode *inode, const char *name, void **buffer, bool alloc);
 int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags);
 int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
 int security_file_permission(struct file *file, int mask);
@@ -1967,7 +1964,7 @@ static inline int security_inode_killpriv(struct dentry *dentry)
        return cap_inode_killpriv(dentry);
 }
 
-static inline int security_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err)
+static inline int security_inode_getsecurity(const struct inode *inode, const char *name, void **buffer, bool alloc)
 {
        return -EOPNOTSUPP;
 }

diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index def131a5ac70085f685b527c6de0f23fccae4d0e..df6b95d2218e26930ef95d0bee2e05187f487659 100644 (file)
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -46,6 +46,7 @@ struct xattr_handler {
                   size_t size, int flags);
 };
 
+ssize_t xattr_getsecurity(struct inode *, const char *, void *, size_t);
 ssize_t vfs_getxattr(struct dentry *, char *, void *, size_t);
 ssize_t vfs_listxattr(struct dentry *d, char *list, size_t size);
 int vfs_setxattr(struct dentry *, char *, void *, size_t, int);

diff --git a/mm/shmem.c b/mm/shmem.c
index ee9024483f6094bac4d6bdac8b798d11e8846fe7..0f246c44a5744ec5aac0930c7896923e96bcb215 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1955,8 +1955,7 @@ static int shmem_xattr_security_get(struct inode *inode, const char *name,
 {
        if (strcmp(name, "") == 0)
                return -EINVAL;
-       return security_inode_getsecurity(inode, name, buffer, size,
-                                         -EOPNOTSUPP);
+       return xattr_getsecurity(inode, name, buffer, size);
 }
 
 static int shmem_xattr_security_set(struct inode *inode, const char *name,

diff --git a/security/dummy.c b/security/dummy.c
index 48d4b0a52737b2e28a8fb2e32d589af2db2463f9..c505122e22dbddec700ea967b604f1a01480399b 100644 (file)
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -402,7 +402,7 @@ static int dummy_inode_killpriv(struct dentry *dentry)
        return 0;
 }
 
-static int dummy_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err)
+static int dummy_inode_getsecurity(const struct inode *inode, const char *name, void **buffer, bool alloc)
 {
        return -EOPNOTSUPP;
 }

diff --git a/security/security.c b/security/security.c
index ca475ca206e4b3afe51ad7bdee1c30fe8398c892..b6c57a6b2ff55d41ca660b232b8bcd95dbd7faed 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -493,11 +493,11 @@ int security_inode_killpriv(struct dentry *dentry)
        return security_ops->inode_killpriv(dentry);
 }
 
-int security_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err)
+int security_inode_getsecurity(const struct inode *inode, const char *name, void **buffer, bool alloc)
 {
        if (unlikely(IS_PRIVATE(inode)))
                return 0;
-       return security_ops->inode_getsecurity(inode, name, buffer, size, err);
+       return security_ops->inode_getsecurity(inode, name, buffer, alloc);
 }
 
 int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index be6de0b8734fd9eb950d8f8ca9e2306621764420..e5ed07510309edb0da10a151095cd3529bf41442 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -136,32 +136,6 @@ static DEFINE_SPINLOCK(sb_security_lock);
 
 static struct kmem_cache *sel_inode_cache;
 
-/* Return security context for a given sid or just the context 
-   length if the buffer is null or length is 0 */
-static int selinux_getsecurity(u32 sid, void *buffer, size_t size)
-{
-       char *context;
-       unsigned len;
-       int rc;
-
-       rc = security_sid_to_context(sid, &context, &len);
-       if (rc)
-               return rc;
-
-       if (!buffer || !size)
-               goto getsecurity_exit;
-
-       if (size < len) {
-               len = -ERANGE;
-               goto getsecurity_exit;
-       }
-       memcpy(buffer, context, len);
-
-getsecurity_exit:
-       kfree(context);
-       return len;
-}
-
 /**
  * selinux_secmark_enabled - Check to see if SECMARK is currently enabled
  *
@@ -2675,14 +2649,27 @@ static int selinux_inode_removexattr (struct dentry *dentry, char *name)
  *
  * Permission check is handled by selinux_inode_getxattr hook.
  */
-static int selinux_inode_getsecurity(const struct inode *inode, const char *name, void *buffer, size_t size, int err)
+static int selinux_inode_getsecurity(const struct inode *inode, const char *name, void **buffer, bool alloc)
 {
+       u32 size;
+       int error;
+       char *context = NULL;
        struct inode_security_struct *isec = inode->i_security;
 
        if (strcmp(name, XATTR_SELINUX_SUFFIX))
                return -EOPNOTSUPP;
 
-       return selinux_getsecurity(isec->sid, buffer, size);
+       error = security_sid_to_context(isec->sid, &context, &size);
+       if (error)
+               return error;
+       error = size;
+       if (alloc) {
+               *buffer = context;
+               goto out_nofree;
+       }
+       kfree(context);
+out_nofree:
+       return error;
 }
 
 static int selinux_inode_setsecurity(struct inode *inode, const char *name,