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Subject[PATCH 2/2] fs: add link restriction audit reporting
Date
Adds audit messages for unexpected link restriction violations so that
system owners will have some sort of potentially actionable information
about misbehaving processes.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/namei.c | 2 ++
include/linux/audit.h | 4 ++++
kernel/audit.c | 21 +++++++++++++++++++++
3 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index e5ad2db..cb3856f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -691,6 +691,7 @@ static inline int may_follow_link(struct path *link, struct nameidata *nd)
return 0;

path_put(&nd->path);
+ audit_log_link_denied("follow_link", link);
return -EACCES;
}

@@ -759,6 +760,7 @@ static int may_linkat(struct path *link)
capable(CAP_FOWNER))
return 0;

+ audit_log_link_denied("linkat", link);
return -EPERM;
}

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 22f292a..36abf2a 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -130,6 +130,7 @@
#define AUDIT_LAST_KERN_ANOM_MSG 1799
#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_INTEGRITY_DATA 1800 /* Data integrity verification */
#define AUDIT_INTEGRITY_METADATA 1801 /* Metadata integrity verification */
#define AUDIT_INTEGRITY_STATUS 1802 /* Integrity enable status */
@@ -687,6 +688,8 @@ 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,
+ struct path *link);
extern void audit_log_lost(const char *message);
#ifdef CONFIG_SECURITY
extern void audit_log_secctx(struct audit_buffer *ab, u32 secid);
@@ -716,6 +719,7 @@ extern int audit_enabled;
#define audit_log_untrustedstring(a,s) do { ; } while (0)
#define audit_log_d_path(b, p, d) do { ; } while (0)
#define audit_log_key(b, k) do { ; } while (0)
+#define audit_log_link_denied(o, l) do { ; } while (0)
#define audit_log_secctx(b,s) do { ; } while (0)
#define audit_enabled 0
#endif
diff --git a/kernel/audit.c b/kernel/audit.c
index 4a3f28d..ea3b7b6 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1456,6 +1456,27 @@ void audit_log_key(struct audit_buffer *ab, char *key)
}

/**
+ * audit_log_link_denied - report a link restriction denial
+ * @operation: specific link opreation
+ * @link: the path that triggered the restriction
+ */
+void audit_log_link_denied(const char *operation, struct path *link)
+{
+ struct audit_buffer *ab;
+
+ ab = audit_log_start(current->audit_context, GFP_KERNEL,
+ AUDIT_ANOM_LINK);
+ audit_log_format(ab, "op=%s action=denied", operation);
+ audit_log_format(ab, " pid=%d comm=", current->pid);
+ audit_log_untrustedstring(ab, current->comm);
+ audit_log_d_path(ab, " path=", link);
+ audit_log_format(ab, " dev=");
+ audit_log_untrustedstring(ab, link->dentry->d_inode->i_sb->s_id);
+ audit_log_format(ab, " ino=%lu", link->dentry->d_inode->i_ino);
+ audit_log_end(ab);
+}
+
+/**
* audit_log_end - end one audit record
* @ab: the audit_buffer
*
--
1.7.0.4


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