Re: [PATCH v4 2/20] lsm: Refactor return value of LSM hook inode_need_killpriv

On Jul 11, 2024 Xu Kuohai xukuohai@huaweicloud.com wrote:

To be consistent with most LSM hooks, convert the return value of hook inode_need_killpriv to 0 or a negative error code.

Before:

• Both hook inode_need_killpriv and func security_inode_need_killpriv return > 0 if security_inode_killpriv is required, 0 if not, and < 0 to abort the operation.

After:

• Both hook inode_need_killpriv and func security_inode_need_killpriv return 0 on success and a negative error code on failure. On success, hook inode_need_killpriv sets output param @need to true if security_inode_killpriv is required, and false if not. When @need is true, func security_inode_need_killpriv sets ATTR_KILL_PRIV flag in @attr; when false, it clears the flag. On failure, @need and @attr remains unchanged.

Signed-off-by: Xu Kuohai xukuohai@huawei.com

fs/attr.c | 5 ++--- fs/inode.c | 4 +--- include/linux/lsm_hook_defs.h | 2 +- include/linux/security.h | 20 ++++++++++++++++---- security/commoncap.c | 12 ++++++++---- security/security.c | 29 ++++++++++++++++++++++++----- 6 files changed, 52 insertions(+), 20 deletions(-)

In general I think a lot of these changes are a good improvement, thank you very much for the time and effort you've spent on this. However, I'm not in favor of passing the new hook parameter as a way of reducing the number of states represented by the security_inode_killpriv() return value. This particular hook may need to remain as one of the odd special cases.

diff --git a/fs/attr.c b/fs/attr.c index 960a310581eb..aaadc721c982 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -427,11 +427,10 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry, attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode); if (ia_valid & ATTR_KILL_PRIV) {

• error = security_inode_need_killpriv(dentry);
  

• error = security_inode_need_killpriv(dentry, &ia_valid);
  

  if (error < 0) return error;

• if (error == 0)
  

• 	ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
  

• attr->ia_valid = ia_valid;
  

  }

/* diff --git a/fs/inode.c b/fs/inode.c index 3a41f83a4ba5..cd335dc3a3bc 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2012,11 +2012,9 @@ int dentry_needs_remove_privs(struct mnt_idmap *idmap, return 0; mask = setattr_should_drop_suidgid(idmap, inode);

• ret = security_inode_need_killpriv(dentry);

• ret = security_inode_need_killpriv(dentry, &mask); if (ret < 0) return ret;

• if (ret)

• mask |= ATTR_KILL_PRIV;
  

  return mask;

} diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index e6e6f8473955..964849de424b 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -165,7 +165,7 @@ LSM_HOOK(int, 0, inode_remove_acl, struct mnt_idmap *idmap, struct dentry *dentry, const char *acl_name) LSM_HOOK(void, LSM_RET_VOID, inode_post_remove_acl, struct mnt_idmap *idmap, struct dentry *dentry, const char *acl_name) -LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry) +LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry, bool *need) LSM_HOOK(int, 0, inode_killpriv, struct mnt_idmap *idmap, struct dentry *dentry) LSM_HOOK(int, -EOPNOTSUPP, inode_getsecurity, struct mnt_idmap *idmap, diff --git a/include/linux/security.h b/include/linux/security.h index 454f96307cb9..1614ef5b2dd2 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -161,7 +161,7 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags); int cap_inode_removexattr(struct mnt_idmap *idmap, struct dentry *dentry, const char *name); -int cap_inode_need_killpriv(struct dentry *dentry); +int cap_inode_need_killpriv(struct dentry *dentry, bool *need); int cap_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry); int cap_inode_getsecurity(struct mnt_idmap *idmap, struct inode *inode, const char *name, void **buffer, @@ -389,7 +389,7 @@ int security_inode_listxattr(struct dentry *dentry); int security_inode_removexattr(struct mnt_idmap *idmap, struct dentry *dentry, const char *name); void security_inode_post_removexattr(struct dentry *dentry, const char *name); -int security_inode_need_killpriv(struct dentry *dentry); +int security_inode_need_killpriv(struct dentry *dentry, int *attr); int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry); int security_inode_getsecurity(struct mnt_idmap *idmap, struct inode *inode, const char *name, @@ -971,9 +971,21 @@ static inline void security_inode_post_removexattr(struct dentry *dentry, const char *name) { } -static inline int security_inode_need_killpriv(struct dentry *dentry) +static inline int security_inode_need_killpriv(struct dentry *dentry, int *attr) {

• return cap_inode_need_killpriv(dentry);

• int rc;
• bool need = false;
• rc = cap_inode_need_killpriv(dentry, &need);
• if (rc < 0)

• return rc;
  

• if (need)

• *attr |= ATTR_KILL_PRIV;
  

• else

• *attr &= ~ATTR_KILL_PRIV;
  

• return 0;

} static inline int security_inode_killpriv(struct mnt_idmap *idmap, diff --git a/security/commoncap.c b/security/commoncap.c index cefad323a0b1..17d6188d22cf 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -286,21 +286,25 @@ int cap_capset(struct cred *new, /**

• cap_inode_need_killpriv - Determine if inode change affects privileges
• @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV

• • @need: If inode_killpriv() is needed
  • Determine if an inode having a change applied that's marked ATTR_KILL_PRIV
  • affects the security markings on that inode, and if it is, should
  • inode_killpriv() be invoked or the change rejected.

• • Return: 1 if security.capability has a value, meaning inode_killpriv()
• • is required, 0 otherwise, meaning inode_killpriv() is not required.

• • Return: Always returns 0. If security.capability has a value, meaning
• • inode_killpriv() is required, @need is set to true.
  */

-int cap_inode_need_killpriv(struct dentry *dentry) +int cap_inode_need_killpriv(struct dentry *dentry, bool *need) { struct inode *inode = d_backing_inode(dentry); int error; error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);

• return error > 0;

• if (error > 0)

• *need = true;
  

• return 0;

} /** diff --git a/security/security.c b/security/security.c index 3475f0cab3da..a4abcd86eb36 100644 --- a/security/security.c +++ b/security/security.c @@ -2490,17 +2490,36 @@ void security_inode_post_removexattr(struct dentry *dentry, const char *name) /**

• security_inode_need_killpriv() - Check if security_inode_killpriv() required
• @dentry: associated dentry

• • @attr: attribute flags
  • Called when an inode has been changed to determine if
  • security_inode_killpriv() should be called.

• • Return: Return <0 on error to abort the inode change operation, return 0 if

• •     security_inode_killpriv() does not need to be called, return >0 if
    

• •     security_inode_killpriv() does need to be called.
    

• • Return: Return 0 on success, negative error code on failure.

• •     On success, set ATTR_KILL_PRIV flag in @attr when @need is true,
    

• •     clears it when false.
    

  */

-int security_inode_need_killpriv(struct dentry *dentry) +int security_inode_need_killpriv(struct dentry *dentry, int *attr) {

• return call_int_hook(inode_need_killpriv, dentry);

• int rc;
• bool need = false;
• struct security_hook_list *hp;
• hlist_for_each_entry(hp, &security_hook_heads.inode_need_killpriv,

• 	     list) {
  

• rc = hp->hook.inode_need_killpriv(dentry, &need);
  

• if (rc < 0)
  

• 	return rc;
  

• if (need)
  

• 	break;
  

• }
• if (need)

• *attr |= ATTR_KILL_PRIV;
  

• else

• *attr &= ~ATTR_KILL_PRIV;
  

• return 0;

} /** -- 2.30.2

-- paul-moore.com