Re: [PATCH 2/2] fs: remove the inode argument to ->d_real() method

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/2/24 11:16, Al Viro wrote:
> On Fri, Feb 02, 2024 at 04:05:09PM +0000, Al Viro wrote:
> 
>> Use After Free.  Really.  And "untrusted" in the function name does not
>> refer to "it might be pointing to unmapped page" - it's just "don't
>> expect anything from the characters you might find there, including
>> the presence of NUL".
> 
> Argh...  s/including/beyond the/ - sorry.  Messed up rewriting the
> sentence.
> 
> "Untrusted" refers to the lack of whitespaces, control characters, '"',
> etc.  What audit_log_untrustedstring(ab, string) expects is
> 	* string pointing to readable memory object
> 	* the object remaining unchanged through the call
> 	* NUL existing somewhere in that object.
> 
> All of those assertions can be violated once the object string
> used to point to has been passed to kmem_cache_free().  Which is what
> can very well happen to filename pointer in this case.

I suppose this would provide a stable name?

diff --git a/security/integrity/ima/ima_api.c 
b/security/integrity/ima/ima_api.c
index 597ea0c4d72f..48ae6911139b 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -244,7 +244,6 @@ int ima_collect_measurement(struct 
integrity_iint_cache *iint,
         const char *audit_cause = "failed";
         struct inode *inode = file_inode(file);
         struct inode *real_inode = d_real_inode(file_dentry(file));
-       const char *filename = file->f_path.dentry->d_name.name;
         struct ima_max_digest_data hash;
         struct kstat stat;
         int result = 0;
@@ -313,11 +312,17 @@ int ima_collect_measurement(struct 
integrity_iint_cache *iint,
                 iint->flags |= IMA_COLLECTED;
  out:
         if (result) {
+               struct qstr *qstr = &file->f_path.dentry->d_name;
+               char buf[NAME_MAX + 1];
+
                 if (file->f_flags & O_DIRECT)
                         audit_cause = "failed(directio)";

+               memcpy(buf, qstr->name, qstr->len);
+               buf[qstr->len] = 0;
+
                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
-                                   filename, "collect_data", audit_cause,
+                                   buf, "collect_data", audit_cause,
                                     result, 0);
         }
         return result;


Regards,
    Stefan