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

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Message-ID: <CAHC9VhSx23JiN6GprskxdEcs9uftJOp03Svh7YJbQLOV91AMiQ@mail.gmail.com>
Date:   Mon, 27 Jul 2020 22:14:26 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        Eric Paris <eparis@...isplace.org>
Subject: Re: [PATCH V3fix ghak120] audit: initialize context values in case of
 mandatory events

On Mon, Jul 27, 2020 at 5:30 PM Richard Guy Briggs <rgb@...hat.com> 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.

> ... 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 <rgb@...hat.com>
> ---
>  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