[PATCH 1/5] security: allow finer granularity in permitting copy-up of security xattrs

Stefan Berger
2024-01-30T21:46:52Z

Copying up xattrs is solely based on the security xattr name. For finer
granularity add a dentry parameter to the security_inode_copy_up_xattr
hook definition, allowing decisions to be based on the xattr content as
well.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
fs/overlayfs/copy_up.c | 2 +-
include/linux/evm.h | 2 +-
include/linux/lsm_hook_defs.h | 3 ++-
include/linux/security.h | 4 ++--
security/integrity/evm/evm_main.c | 2 +-
security/security.c | 7 ++++---
security/selinux/hooks.c | 2 +-
security/smack/smack_lsm.c | 2 +-
8 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index b8e25ca51016..bd9ddcefb7a7 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -114,7 +114,7 @@ int ovl_copy_xattr(struct super_block *sb, const struct path *oldpath, struct de
if (ovl_is_private_xattr(sb, name))
continue;

- error = security_inode_copy_up_xattr(name);
+ error = security_inode_copy_up_xattr(old, name);
if (error < 0 && error != -EOPNOTSUPP)
break;
if (error == 1) {
diff --git a/include/linux/evm.h b/include/linux/evm.h
index 36ec884320d9..d8c0343436b8 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -31,7 +31,7 @@ extern void evm_inode_post_setxattr(struct dentry *dentry,
const char *xattr_name,
const void *xattr_value,
size_t xattr_value_len);
-extern int evm_inode_copy_up_xattr(const char *name);
+extern int evm_inode_copy_up_xattr(struct dentry *dentry, const char *name);
extern int evm_inode_removexattr(struct mnt_idmap *idmap,
struct dentry *dentry, const char *xattr_name);
extern void evm_inode_post_removexattr(struct dentry *dentry,
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 185924c56378..7dd61f51d84a 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -163,7 +163,8 @@ LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,
size_t buffer_size)
LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
-LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
+LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, struct dentry *src,
+ const char *name)
LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
struct kernfs_node *kn)
LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
diff --git a/include/linux/security.h b/include/linux/security.h
index d0eb20f90b26..9fc9ca6284d6 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -387,7 +387,7 @@ int security_inode_setsecurity(struct inode *inode, const char *name, const void
int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
void security_inode_getsecid(struct inode *inode, u32 *secid);
int security_inode_copy_up(struct dentry *src, struct cred **new);
-int security_inode_copy_up_xattr(const char *name);
+int security_inode_copy_up_xattr(struct dentry *src, const char *name);
int security_kernfs_init_security(struct kernfs_node *kn_dir,
struct kernfs_node *kn);
int security_file_permission(struct file *file, int mask);
@@ -980,7 +980,7 @@ static inline int security_kernfs_init_security(struct kernfs_node *kn_dir,
return 0;
}

-static inline int security_inode_copy_up_xattr(const char *name)
+static inline int security_inode_copy_up_xattr(struct dentry *src, const char *name)
{
return -EOPNOTSUPP;
}
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index cc7956d7878b..2555aa4501ae 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -896,7 +896,7 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
evm_update_evmxattr(dentry, NULL, NULL, 0);
}

-int evm_inode_copy_up_xattr(const char *name)
+int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
{
if (strcmp(name, XATTR_NAME_EVM) == 0)
return 1; /* Discard */
diff --git a/security/security.c b/security/security.c
index 0144a98d3712..ee63863c1dc0 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2596,6 +2596,7 @@ EXPORT_SYMBOL(security_inode_copy_up);

/**
* security_inode_copy_up_xattr() - Filter xattrs in an overlayfs copy-up op
+ * @src: union dentry of copy-up file
* @name: xattr name
*
* Filter the xattrs being copied up when a unioned file is copied up from a
@@ -2606,7 +2607,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
* if the security module does not know about attribute, or a negative
* error code to abort the copy up.
*/
-int security_inode_copy_up_xattr(const char *name)
+int security_inode_copy_up_xattr(struct dentry *src, const char *name)
{
struct security_hook_list *hp;
int rc;
@@ -2618,12 +2619,12 @@ int security_inode_copy_up_xattr(const char *name)
*/
hlist_for_each_entry(hp,
&security_hook_heads.inode_copy_up_xattr, list) {
- rc = hp->hook.inode_copy_up_xattr(name);
+ rc = hp->hook.inode_copy_up_xattr(src, name);
if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
return rc;
}

- return evm_inode_copy_up_xattr(name);
+ return evm_inode_copy_up_xattr(src, name);
}
EXPORT_SYMBOL(security_inode_copy_up_xattr);

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a6bf90ace84c..ebb8876837c6 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3530,7 +3530,7 @@ static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
return 0;
}

-static int selinux_inode_copy_up_xattr(const char *name)
+static int selinux_inode_copy_up_xattr(struct dentry *dentry, const char *name)
{
/* The copy_up hook above sets the initial context on an inode, but we
* don't then want to overwrite it by blindly copying all the lower
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 0fdbf04cc258..bffca165f07f 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4873,7 +4873,7 @@ static int smack_inode_copy_up(struct dentry *dentry, struct cred **new)
return 0;
}

-static int smack_inode_copy_up_xattr(const char *name)
+static int smack_inode_copy_up_xattr(struct dentry *src, const char *name)
{
/*
* Return 1 if this is the smack access Smack attribute.
--
2.43.0