Re: [PATCH] audit: add FSCONFIG auxiliary record to log filesystem configuration

From: Richard Guy Briggs

Date: Tue Jul 21 2026 - 21:46:55 EST

On 2026-07-13 14:00, Ricardo Robaina wrote:
> Modern mount tools (util-linux >= 2.39.1) use the new mount API
> (fsopen, fsconfig, fsmount, move_mount) instead of the legacy mount(2)
> syscall. The generic SYSCALL audit record logs the fsconfig syscall but
> does not capture the configuration parameters, creating an audit gap for
> critical mount information such as the device being mounted.
>
> Add an FSCONFIG auxiliary record that logs the command type, parameter
> name (key), parameter value, and aux parameter passed to fsconfig(2).
>
> ----
> type=SYSCALL : syscall=fsconfig a1=FSCONFIG_SET_STRING ...

This looks like it is missing "a0=..."?

> type=FSCONFIG : fs_cmd=1 fs_key=source fs_val="tmpfs" fs_aux=0
> ----
> type=SYSCALL : syscall=fsconfig a1=FSCONFIG_CMD_CREATE ...

This looks like it is missing "a0=..."?
I'm guessing this isn't actually real test output?

> type=FSCONFIG : fs_cmd=6 fs_key=(null) fs_val=(null) fs_aux=0

Was there a fs_key output here that didn't make it due to the issue below?

> ----
> type=SYSCALL : syscall=fsconfig a0=0x4 a1=FSCONFIG_SET_BINARY ...
> type=FSCONFIG : fs_cmd=2 fs_key=hidepid fs_val="<binary>" fs_aux=4
>
> Link: https://github.com/linux-audit/audit-kernel/issues/153
> Signed-off-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>
> ---
> fs/fsopen.c | 7 +++++++
> include/linux/audit.h | 13 +++++++++++++
> include/uapi/linux/audit.h | 1 +
> kernel/auditsc.c | 27 +++++++++++++++++++++++++++
> 4 files changed, 48 insertions(+)
>
> diff --git a/fs/fsopen.c b/fs/fsopen.c
> index ae19e5136598..9b3c02f59df4 100644
> --- a/fs/fsopen.c
> +++ b/fs/fsopen.c
> @@ -15,6 +15,7 @@
> #include <linux/namei.h>
> #include <linux/file.h>
> #include <uapi/linux/mount.h>
> +#include <linux/audit.h>
> #include "internal.h"
> #include "mount.h"
>
> @@ -357,6 +358,7 @@ SYSCALL_DEFINE5(fsconfig,
> struct fs_context *fc;
> int ret;
> int lookup_flags = 0;
> + const char *value_str = NULL;
>
> struct fs_parameter param = {
> .type = fs_value_is_undefined,
> @@ -423,6 +425,7 @@ SYSCALL_DEFINE5(fsconfig,
> goto out_key;
> }
> param.size = strlen(param.string);
> + value_str = param.string;
> break;
> case FSCONFIG_SET_BINARY:
> param.type = fs_value_is_blob;
> @@ -432,6 +435,7 @@ SYSCALL_DEFINE5(fsconfig,
> ret = PTR_ERR(param.blob);
> goto out_key;
> }
> + value_str = "<binary>";
> break;
> case FSCONFIG_SET_PATH_EMPTY:
> lookup_flags = LOOKUP_EMPTY;
> @@ -445,6 +449,7 @@ SYSCALL_DEFINE5(fsconfig,
> }
> param.dirfd = aux;
> param.size = strlen(param.name->name);
> + value_str = param.name->name;
> break;
> case FSCONFIG_SET_FD:
> param.type = fs_value_is_file;
> @@ -458,6 +463,8 @@ SYSCALL_DEFINE5(fsconfig,
> break;
> }
>
> + audit_log_fsconfig(cmd, param.key, value_str, aux);
> +
> ret = mutex_lock_interruptible(&fc->uapi_mutex);
> if (ret == 0) {
> ret = vfs_fsconfig_locked(fc, cmd, &param);
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 45abb3722d30..978eb881974c 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -449,6 +449,8 @@ extern void __audit_tk_injoffset(struct timespec64 offset);
> extern void __audit_ntp_log(const struct audit_ntp_data *ad);
> extern void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
> enum audit_nfcfgop op, gfp_t gfp);
> +extern void __audit_log_fsconfig(unsigned int cmd, const char *key,
> + const char *value, int aux);
>
> static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
> {
> @@ -598,6 +600,13 @@ static inline void audit_log_nfcfg(const char *name, u8 af,
> __audit_log_nfcfg(name, af, nentries, op, gfp);
> }
>
> +static inline void audit_log_fsconfig(unsigned int cmd, const char *key,
> + const char *value, int aux)
> +{
> + if (!audit_dummy_context())
> + __audit_log_fsconfig(cmd, key, value, aux);
> +}
> +
> extern int audit_n_rules;
> extern int audit_signals;
> #else /* CONFIG_AUDITSYSCALL */
> @@ -730,6 +739,10 @@ static inline void audit_log_nfcfg(const char *name, u8 af,
> enum audit_nfcfgop op, gfp_t gfp)
> { }
>
> +static inline void audit_log_fsconfig(unsigned int cmd, const char *key,
> + const char *value, int aux)
> +{ }
> +
> #define audit_n_rules 0
> #define audit_signals 0
> #endif /* CONFIG_AUDITSYSCALL */
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index e8f5ce677df7..5cd0eb602528 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -122,6 +122,7 @@
> #define AUDIT_OPENAT2 1337 /* Record showing openat2 how args */
> #define AUDIT_DM_CTRL 1338 /* Device Mapper target control */
> #define AUDIT_DM_EVENT 1339 /* Device Mapper events */
> +#define AUDIT_FSCONFIG 1341 /* Record showing fsconfig args */
>
> #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 6610e667c728..222bf79ee9bd 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2882,6 +2882,33 @@ void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
> }
> EXPORT_SYMBOL_GPL(__audit_log_nfcfg);
>
> +void __audit_log_fsconfig(unsigned int cmd, const char *key,
> + const char *value, int aux)
> +{
> + struct audit_buffer *ab;
> +
> + ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_FSCONFIG);
> + if (!ab)
> + return;
> +
> + audit_log_format(ab, "fs_cmd=%u", cmd);
> + audit_log_format(ab, " fs_key=");
> + if (value)

This looks like it should be "if (key)".

> + audit_log_untrustedstring(ab, key);
> + else
> + audit_log_format(ab, "(null)");
> +
> + audit_log_format(ab, " fs_val=");
> + if (value)
> + audit_log_untrustedstring(ab, value);
> + else
> + audit_log_format(ab, "(null)");
> +
> + audit_log_format(ab, " fs_aux=%d", aux);
> +
> + audit_log_end(ab);
> +}
> +
> static void audit_log_task(struct audit_buffer *ab)
> {
> kuid_t auid, uid;
> --
> 2.53.0

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
Upstream IRC: SunRaycer
Voice: +1.613.860 2354 SMS: +1.613.518.6570