Re: [PATCH v4 3/3] audit: add OPENAT2 record to list how

From: Christian Brauner
Date: Thu May 20 2021 - 04:03:31 EST

On Wed, May 19, 2021 at 04:00:22PM -0400, Richard Guy Briggs wrote:
> Since the openat2(2) syscall uses a struct open_how pointer to communicate
> its parameters they are not usefully recorded by the audit SYSCALL record's
> four existing arguments.
>
> Add a new audit record type OPENAT2 that reports the parameters in its
> third argument, struct open_how with fields oflag, mode and resolve.
>
> The new record in the context of an event would look like:
> time->Wed Mar 17 16:28:53 2021
> type=PROCTITLE msg=audit(1616012933.531:184): proctitle=73797363616C6C735F66696C652F6F70656E617432002F746D702F61756469742D7465737473756974652D737641440066696C652D6F70656E617432
> type=PATH msg=audit(1616012933.531:184): item=1 name="file-openat2" inode=29 dev=00:1f mode=0100600 ouid=0 ogid=0 rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=CREATE cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
> type=PATH msg=audit(1616012933.531:184): item=0 name="/root/rgb/git/audit-testsuite/tests" inode=25 dev=00:1f mode=040700 ouid=0 ogid=0 rdev=00:00 obj=unconfined_u:object_r:user_tmp_t:s0 nametype=PARENT cap_fp=0 cap_fi=0 cap_fe=0 cap_fver=0 cap_frootid=0
> type=CWD msg=audit(1616012933.531:184): cwd="/root/rgb/git/audit-testsuite/tests"
> type=OPENAT2 msg=audit(1616012933.531:184): oflag=0100302 mode=0600 resolve=0xa
> type=SYSCALL msg=audit(1616012933.531:184): arch=c000003e syscall=437 success=yes exit=4 a0=3 a1=7ffe315f1c53 a2=7ffe315f1550 a3=18 items=2 ppid=528 pid=540 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=1 comm="openat2" exe="/root/rgb/git/audit-testsuite/tests/syscalls_file/openat2" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key="testsuite-1616012933-bjAUcEPO"
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/d23fbb89186754487850367224b060e26f9b7181.1621363275.git.rgb@xxxxxxxxxx
> ---
> fs/open.c | 2 ++
> include/linux/audit.h | 10 ++++++++++
> include/uapi/linux/audit.h | 1 +
> kernel/audit.h | 2 ++
> kernel/auditsc.c | 18 +++++++++++++++++-
> 5 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index e53af13b5835..2a15bec0cf6d 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1235,6 +1235,8 @@ SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename,
> if (err)
> return err;
>
> + audit_openat2_how(&tmp);
> +
> /* O_LARGEFILE is only allowed for non-O_PATH. */
> if (!(tmp.flags & O_PATH) && force_o_largefile())
> tmp.flags |= O_LARGEFILE;
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 283bc91a6932..580a52caf16f 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -399,6 +399,7 @@ extern int __audit_log_bprm_fcaps(struct linux_binprm *bprm,
> const struct cred *old);
> extern void __audit_log_capset(const struct cred *new, const struct cred *old);
> extern void __audit_mmap_fd(int fd, int flags);
> +extern void __audit_openat2_how(struct open_how *how);
> extern void __audit_log_kern_module(char *name);
> extern void __audit_fanotify(unsigned int response);
> extern void __audit_tk_injoffset(struct timespec64 offset);
> @@ -495,6 +496,12 @@ static inline void audit_mmap_fd(int fd, int flags)
> __audit_mmap_fd(fd, flags);
> }
>
> +static inline void audit_openat2_how(struct open_how *how)
> +{
> + if (unlikely(!audit_dummy_context()))
> + __audit_openat2_how(how);
> +}
> +
> static inline void audit_log_kern_module(char *name)
> {
> if (!audit_dummy_context())
> @@ -646,6 +653,9 @@ static inline void audit_log_capset(const struct cred *new,
> static inline void audit_mmap_fd(int fd, int flags)
> { }
>
> +static inline void audit_openat2_how(struct open_how *how)
> +{ }
> +
> static inline void audit_log_kern_module(char *name)
> {
> }
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index cd2d8279a5e4..67aea2370c6d 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -118,6 +118,7 @@
> #define AUDIT_TIME_ADJNTPVAL 1333 /* NTP value adjustment */
> #define AUDIT_BPF 1334 /* BPF subsystem */
> #define AUDIT_EVENT_LISTENER 1335 /* Task joined multicast read socket */
> +#define AUDIT_OPENAT2 1336 /* Record showing openat2 how args */
>
> #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> diff --git a/kernel/audit.h b/kernel/audit.h
> index 1522e100fd17..c5af17905976 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -11,6 +11,7 @@
> #include <linux/skbuff.h>
> #include <uapi/linux/mqueue.h>
> #include <linux/tty.h>
> +#include <uapi/linux/openat2.h> // struct open_how
>
> /* AUDIT_NAMES is the number of slots we reserve in the audit_context
> * for saving names from getname(). If we get more names we will allocate
> @@ -185,6 +186,7 @@ struct audit_context {
> int fd;
> int flags;
> } mmap;
> + struct open_how openat2;
> struct {
> int argc;
> } execve;
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 3f59ab209dfd..faf2485323a9 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -76,7 +76,7 @@
> #include <linux/fsnotify_backend.h>
> #include <uapi/linux/limits.h>
> #include <uapi/linux/netfilter/nf_tables.h>
> -#include <uapi/linux/openat2.h>
> +#include <uapi/linux/openat2.h> // struct open_how
>
> #include "audit.h"
>
> @@ -1319,6 +1319,12 @@ static void show_special(struct audit_context *context, int *call_panic)
> audit_log_format(ab, "fd=%d flags=0x%x", context->mmap.fd,
> context->mmap.flags);
> break;
> + case AUDIT_OPENAT2:
> + audit_log_format(ab, "oflag=0%llo mode=0%llo resolve=0x%llx",

Hm, should we maybe follow the struct member names for all entries, i.e.
replace s/oflag/flags?

Otherwise
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

> + context->openat2.flags,
> + context->openat2.mode,
> + context->openat2.resolve);
> + break;
> case AUDIT_EXECVE:
> audit_log_execve_info(context, &ab);
> break;
> @@ -2549,6 +2555,16 @@ void __audit_mmap_fd(int fd, int flags)
> context->type = AUDIT_MMAP;
> }
>
> +void __audit_openat2_how(struct open_how *how)
> +{
> + struct audit_context *context = audit_context();
> +
> + context->openat2.flags = how->flags;
> + context->openat2.mode = how->mode;
> + context->openat2.resolve = how->resolve;
> + context->type = AUDIT_OPENAT2;
> +}
> +
> void __audit_log_kern_module(char *name)
> {
> struct audit_context *context = audit_context();
> --
> 2.27.0
>