[PATCH v2] audit: Report suspicious O_CREAT usage

Kees Cook
2019-10-01T16:48:52Z

This renames the very specific audit_log_link_denied() to
audit_log_path_denied() and adds the AUDIT_* type as an argument. This
allows for the creation of the new AUDIT_ANOM_CREAT that can be used to
report the fifo/regular file creation restrictions that were introduced
in commit 30aba6656f61 ("namei: allow restricted O_CREAT of FIFOs and
regular files"). Additionally further clarifies the existing
"operations" strings.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v2:
- fix build failure typo in CONFIG_AUDIT=n case
- improve operations naming (paul)
---
fs/namei.c | 8 ++++++--
include/linux/audit.h | 5 +++--
include/uapi/linux/audit.h | 1 +
kernel/audit.c | 11 ++++++-----
4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 671c3c1a3425..2d5d245ae723 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -925,7 +925,7 @@ static inline int may_follow_link(struct nameidata *nd)
return -ECHILD;

audit_inode(nd->name, nd->stack[0].link.dentry, 0);
- audit_log_link_denied("follow_link");
+ audit_log_path_denied(AUDIT_ANOM_LINK, "sticky_follow_link");
return -EACCES;
}

@@ -993,7 +993,7 @@ static int may_linkat(struct path *link)
if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
return 0;

- audit_log_link_denied("linkat");
+ audit_log_path_denied(AUDIT_ANOM_LINK, "unowned_linkat");
return -EPERM;
}

@@ -1031,6 +1031,10 @@ static int may_create_in_sticky(struct dentry * const dir,
(dir->d_inode->i_mode & 0020 &&
((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
(sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
+ const char *operation = S_ISFIFO(inode->i_mode) ?
+ "sticky_create_fifo" :
+ "sticky_create_regular";
+ audit_log_path_denied(AUDIT_ANOM_CREAT, operation);
return -EACCES;
}
return 0;
diff --git a/include/linux/audit.h b/include/linux/audit.h
index aee3dc9eb378..f9ceae57ca8d 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -156,7 +156,8 @@ extern void audit_log_d_path(struct audit_buffer *ab,
const struct path *path);
extern void audit_log_key(struct audit_buffer *ab,
char *key);
-extern void audit_log_link_denied(const char *operation);
+extern void audit_log_path_denied(int type,
+ const char *operation);
extern void audit_log_lost(const char *message);

extern int audit_log_task_context(struct audit_buffer *ab);
@@ -217,7 +218,7 @@ static inline void audit_log_d_path(struct audit_buffer *ab,
{ }
static inline void audit_log_key(struct audit_buffer *ab, char *key)
{ }
-static inline void audit_log_link_denied(const char *string)
+static inline void audit_log_path_denied(int type, const char *operation)
{ }
static inline int audit_log_task_context(struct audit_buffer *ab)
{
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index c89c6495983d..3ad935527177 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -143,6 +143,7 @@
#define AUDIT_ANOM_PROMISCUOUS 1700 /* Device changed promiscuous mode */
#define AUDIT_ANOM_ABEND 1701 /* Process ended abnormally */
#define AUDIT_ANOM_LINK 1702 /* Suspicious use of file links */
+#define AUDIT_ANOM_CREAT 1703 /* Suspicious file creation */
#define AUDIT_INTEGRITY_DATA 1800 /* Data integrity verification */
#define AUDIT_INTEGRITY_METADATA 1801 /* Metadata integrity verification */
#define AUDIT_INTEGRITY_STATUS 1802 /* Integrity enable status */
diff --git a/kernel/audit.c b/kernel/audit.c
index da8dc0db5bd3..d75485aa25ff 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -2155,18 +2155,19 @@ void audit_log_task_info(struct audit_buffer *ab)
EXPORT_SYMBOL(audit_log_task_info);

/**
- * audit_log_link_denied - report a link restriction denial
- * @operation: specific link operation
+ * audit_log_path_denied - report a path restriction denial
+ * @type: audit message type (AUDIT_ANOM_LINK, AUDIT_ANOM_CREAT, etc)
+ * @operation: specific operation name
*/
-void audit_log_link_denied(const char *operation)
+void audit_log_path_denied(int type, const char *operation)
{
struct audit_buffer *ab;

if (!audit_enabled || audit_dummy_context())
return;

- /* Generate AUDIT_ANOM_LINK with subject, operation, outcome. */
- ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_ANOM_LINK);
+ /* Generate log with subject, operation, outcome. */
+ ab = audit_log_start(audit_context(), GFP_KERNEL, type);
if (!ab)
return;
audit_log_format(ab, "op=%s", operation);
--
2.17.1

--
Kees Cook