Thread (6 messages) 6 messages, 2 authors, 2020-07-29

Re: [PATCH V3fix ghak120] audit: initialize context values in case of mandatory events

From: Paul Moore <paul@paul-moore.com>
Date: 2020-07-28 02:14:41
Also in: lkml

On Mon, Jul 27, 2020 at 5:30 PM Richard Guy Briggs [off-list ref] wrote:
Issue ghak120 enabled syscall records to accompany required records when
no rules are present to trigger the storage of syscall context.  A
reported issue showed that the cwd was not always initialized.  That
issue was already resolved ...
Yes and no.  Yes, it appears to be resolved in v5.8-rc1 and above, but
the problematic commit is in v5.7 and I'm not sure backporting the fix
in v5.8-rcX plus this patch is the right thing to do for a released
kernel.  The lowest risk fix for v5.7 at this point is to do a revert;
regardless of what happens with this patch and v5.8-rcX please post a
revert for the audit/stable-5.7 tree as soon as you can.
quoted hunk ↗ jump to hunk
... but a review of all other records that could
be triggered at the time of a syscall record revealed other potential
values that could be missing or misleading.  Initialize them.

The fds array is reset to -1 after the first syscall to indicate it
isn't valid any more, but was never set to -1 when the context was
allocated to indicate it wasn't yet valid.

The audit_inode* functions can be called without going through
getname_flags() or getname_kernel() that sets audit_names and cwd, so
set the cwd if it has not already been done so due to audit_names being
valid.

The LSM dump_common_audit_data() LSM_AUDIT_DATA_NET:AF_UNIX case was
missed with the ghak96 patch, so add that case here.

Please see issue https://github.com/linux-audit/audit-kernel/issues/120
Please see issue https://github.com/linux-audit/audit-kernel/issues/96
Passes audit-testsuite.

Signed-off-by: Richard Guy Briggs <redacted>
---
 kernel/auditsc.c     | 3 +++
 security/lsm_audit.c | 1 +
 2 files changed, 4 insertions(+)
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 6884b50069d1..2f97618e6a34 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -929,6 +929,7 @@ static inline struct audit_context *audit_alloc_context(enum audit_state state)
        context->prio = state == AUDIT_RECORD_CONTEXT ? ~0ULL : 0;
        INIT_LIST_HEAD(&context->killed_trees);
        INIT_LIST_HEAD(&context->names_list);
+       context->fds[0] = -1;
        return context;
 }
@@ -2076,6 +2077,7 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
        }
        handle_path(dentry);
        audit_copy_inode(n, dentry, inode, flags & AUDIT_INODE_NOEVAL);
+       _audit_getcwd(context);
 }

 void __audit_file(const struct file *file)
@@ -2194,6 +2196,7 @@ void __audit_inode_child(struct inode *parent,
                audit_copy_inode(found_child, dentry, inode, 0);
        else
                found_child->ino = AUDIT_INO_UNSET;
+       _audit_getcwd(context);
 }
 EXPORT_SYMBOL_GPL(__audit_inode_child);
diff --git a/security/lsm_audit.c b/security/lsm_audit.c
index 53d0d183db8f..e93077612246 100644
--- a/security/lsm_audit.c
+++ b/security/lsm_audit.c
@@ -369,6 +369,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
                                        audit_log_untrustedstring(ab, p);
                                else
                                        audit_log_n_hex(ab, p, len);
+                               audit_getcwd();
                                break;
                        }
                }
I understand the "fds[0] = -1" fix in audit_alloc_context()
(ironically, the kzalloc() which is supposed to help with cases like
this, hurts us with this particular field), but I'm still not quite
seeing why we need to sprinkle audit_getcwd() calls everywhere to fix
this bug (this seems more like a feature add than a bigfix).  Yes,
they may fix the problem but it seems like simply adding a
context->pwd test in audit_log_name() similar to what we do in
audit_log_exit() is the correct fix.

We are currently at -rc7 and this really needs to land before v5.8 is
released, presumably this weekend; this means a small and limited bug
fix patch is what is needed.

-- 
paul moore
www.paul-moore.com
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