Add a new LSM hook called before inode's setxattr. It is required for
LSM to be able to reliably replace the xattr's value to be set to
filesystem in __vfs_setxattr_noperm(). Useful for mapped values, like in
the upcoming Smack namespace patches.
Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@xxxxxxxxxxx>
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
---
fs/xattr.c | 10 ++++++++++
include/linux/lsm_hooks.h | 9 +++++++++
include/linux/security.h | 10 ++++++++++
security/security.c | 12 ++++++++++++
4 files changed, 41 insertions(+)
diff --git a/fs/xattr.c b/fs/xattr.c
index 072fee1..cbc8d19 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -100,12 +100,22 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
if (issec)
inode->i_flags &= ~S_NOSEC;
if (inode->i_op->setxattr) {
+ bool alloc = false;
+
+ error = security_inode_pre_setxattr(dentry, name, &value,
+ &size, flags, &alloc);
+ if (error)
+ return error;
+
error = inode->i_op->setxattr(dentry, name, value, size, flags);
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_setxattr(dentry, name, value,
size, flags);
}
+
+ if (alloc)
+ kfree(value);
} else if (issec) {
const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
error = security_inode_setsecurity(inode, suffix, value,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 4f16640..85bfdde 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -349,6 +349,11 @@
* Check permission before setting the extended attributes
* @value identified by @name for @dentry.
* Return 0 if permission is granted.
+ * @inode_pre_setxattr:
+ * Be able to do some operation before setting the @value identified
+ * by @name on the filesystem. Replacing the @value and its @size is
+ * possible. Useful for mapped values. Set @alloc to true if @value
+ * needs to be kfreed afterwards.
* @inode_post_setxattr:
* Update inode security field after successful setxattr operation.
* @value identified by @name for @dentry.
@@ -1448,6 +1453,9 @@ union security_list_options {
int (*inode_getattr)(const struct path *path);
int (*inode_setxattr)(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags);
+ int (*inode_pre_setxattr)(struct dentry *dentry, const char *name,
+ const void **value, size_t *size,
+ int flags, bool *alloc);
void (*inode_post_setxattr)(struct dentry *dentry, const char *name,
const void *value, size_t size,
int flags);
@@ -1730,6 +1738,7 @@ struct security_hook_heads {
struct list_head inode_setattr;
struct list_head inode_getattr;
struct list_head inode_setxattr;
+ struct list_head inode_pre_setxattr;
struct list_head inode_post_setxattr;
struct list_head inode_getxattr;
struct list_head inode_listxattr;
diff --git a/include/linux/security.h b/include/linux/security.h
index 12bd011..4de4865 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -263,6 +263,9 @@ int security_inode_setattr(struct dentry *dentry, struct iattr *attr);
int security_inode_getattr(const struct path *path);
int security_inode_setxattr(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags);
+int security_inode_pre_setxattr(struct dentry *dentry, const char *name,
+ const void **value, size_t *size, int flags,
+ bool *alloc);
void security_inode_post_setxattr(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags);
int security_inode_getxattr(struct dentry *dentry, const char *name);
@@ -691,6 +694,13 @@ static inline int security_inode_setxattr(struct dentry *dentry,
return cap_inode_setxattr(dentry, name, value, size, flags);
}
+static inline int security_inode_pre_setxattr(struct dentry *dentry,
+ const char *name, const void **value,
+ size_t *size, int flags, bool *alloc)
+{
+ return 0;
+}
+
static inline void security_inode_post_setxattr(struct dentry *dentry,
const char *name, const void *value, size_t size, int flags)
{ }
diff --git a/security/security.c b/security/security.c
index abfc207..75d46b6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -644,6 +644,16 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
return evm_inode_setxattr(dentry, name, value, size);
}
+int security_inode_pre_setxattr(struct dentry *dentry, const char *name,
+ const void **value, size_t *size, int flags,
+ bool *alloc)
+{
+ if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+ return 0;
+ return call_int_hook(inode_pre_setxattr, 0, dentry, name, value, size,
+ flags, alloc);
+}
+
void security_inode_post_setxattr(struct dentry *dentry, const char *name,
const void *value, size_t size, int flags)
{
@@ -1662,6 +1672,8 @@ struct security_hook_heads security_hook_heads = {
LIST_HEAD_INIT(security_hook_heads.inode_getattr),
.inode_setxattr =
LIST_HEAD_INIT(security_hook_heads.inode_setxattr),
+ .inode_pre_setxattr =
+ LIST_HEAD_INIT(security_hook_heads.inode_pre_setxattr),
.inode_post_setxattr =
LIST_HEAD_INIT(security_hook_heads.inode_post_setxattr),
.inode_getxattr =
--
2.4.3
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