Re: [PATCH ghak96] audit: set cwd in audit context for file-related LSM audit records

[Casey Schaufler]

On 4/2/2020 7:13 AM, Vladis Dronov wrote:
> Set a current working directory in an audit context for the following record
> types in dump_common_audit_data(): LSM_AUDIT_DATA_PATH, LSM_AUDIT_DATA_FILE,
> LSM_AUDIT_DATA_IOCTL_OP, LSM_AUDIT_DATA_DENTRY, LSM_AUDIT_DATA_INODE so a
> separate CWD record is emitted later.
>
> Link: https://github.com/linux-audit/audit-kernel/issues/96

I don't have a problem with the patch, but it sure would be nice
if you explained why these events "could use a CWD record".

> Signed-off-by: Vladis Dronov <vdronov@xxxxxxxxxx>
> ---
> out-of-commit-message-note:
>
> Hello,
> Honestly, I'm not sure about "if (!context->in_syscall)" check in
> __audit_getcwd(). It was copied from __audit_getname() and I do
> not quite understand why it is there and if __audit_getcwd() needs
> it. If you have an idea on this, could you please, tell?
>
>  include/linux/audit.h |  9 ++++++++-
>  kernel/auditsc.c      | 17 +++++++++++++++++
>  security/lsm_audit.c  |  5 +++++
>  3 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index f9ceae57ca8d..b4306abc5891 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -268,7 +268,7 @@ extern void __audit_syscall_entry(int major, unsigned long a0, unsigned long a1,
>  extern void __audit_syscall_exit(int ret_success, long ret_value);
>  extern struct filename *__audit_reusename(const __user char *uptr);
>  extern void __audit_getname(struct filename *name);
> -
> +extern void __audit_getcwd(void);
>  extern void __audit_inode(struct filename *name, const struct dentry *dentry,
>  				unsigned int flags);
>  extern void __audit_file(const struct file *);
> @@ -327,6 +327,11 @@ static inline void audit_getname(struct filename *name)
>  	if (unlikely(!audit_dummy_context()))
>  		__audit_getname(name);
>  }
> +static inline void audit_getcwd(void)
> +{
> +	if (unlikely(!audit_dummy_context()))
> +		__audit_getcwd();
> +}
>  static inline void audit_inode(struct filename *name,
>  				const struct dentry *dentry,
>  				unsigned int aflags) {
> @@ -545,6 +550,8 @@ static inline struct filename *audit_reusename(const __user char *name)
>  }
>  static inline void audit_getname(struct filename *name)
>  { }
> +static inline void audit_getcwd(void)
> +{ }
>  static inline void __audit_inode(struct filename *name,
>  					const struct dentry *dentry,
>  					unsigned int flags)
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 814406a35db1..16316032ef9f 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1890,6 +1890,23 @@ void __audit_getname(struct filename *name)
>  		get_fs_pwd(current->fs, &context->pwd);
>  }
>  
> +/**
> + * __audit_getcwd - set a current working directory
> + *
> + * Set a current working directory of an audited process for this context.
> + * Called from security/lsm_audit.c:dump_common_audit_data().
> + */
> +void __audit_getcwd(void)
> +{
> +	struct audit_context *context = audit_context();
> +
> +	if (!context->in_syscall)
> +		return;
> +
> +	if (!context->pwd.dentry)
> +		get_fs_pwd(current->fs, &context->pwd);
> +}
> +
>  static inline int audit_copy_fcaps(struct audit_names *name,
>  				   const struct dentry *dentry)
>  {
> diff --git a/security/lsm_audit.c b/security/lsm_audit.c
> index 2d2bf49016f4..7c555621c2bd 100644
> --- a/security/lsm_audit.c
> +++ b/security/lsm_audit.c
> @@ -241,6 +241,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  			audit_log_untrustedstring(ab, inode->i_sb->s_id);
>  			audit_log_format(ab, " ino=%lu", inode->i_ino);
>  		}
> +		audit_getcwd();
>  		break;
>  	}
>  	case LSM_AUDIT_DATA_FILE: {
> @@ -254,6 +255,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  			audit_log_untrustedstring(ab, inode->i_sb->s_id);
>  			audit_log_format(ab, " ino=%lu", inode->i_ino);
>  		}
> +		audit_getcwd();
>  		break;
>  	}
>  	case LSM_AUDIT_DATA_IOCTL_OP: {
> @@ -269,6 +271,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  		}
>  
>  		audit_log_format(ab, " ioctlcmd=0x%hx", a->u.op->cmd);
> +		audit_getcwd();
>  		break;
>  	}
>  	case LSM_AUDIT_DATA_DENTRY: {
> @@ -283,6 +286,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  			audit_log_untrustedstring(ab, inode->i_sb->s_id);
>  			audit_log_format(ab, " ino=%lu", inode->i_ino);
>  		}
> +		audit_getcwd();
>  		break;
>  	}
>  	case LSM_AUDIT_DATA_INODE: {
> @@ -300,6 +304,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  		audit_log_format(ab, " dev=");
>  		audit_log_untrustedstring(ab, inode->i_sb->s_id);
>  		audit_log_format(ab, " ino=%lu", inode->i_ino);
> +		audit_getcwd();
>  		break;
>  	}
>  	case LSM_AUDIT_DATA_TASK: {