AUDIT: Avoid log pollution by untrusted strings.

We log strings from userspace, such as arguments to open(). These could
be formatted to contain \n followed by fake audit log entries. Provide
a function for logging such strings, which gives a hex dump when the
string contains anything but basic printable ASCII characters. Use it
for logging filenames.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

3 files changed, 34 insertions, 4 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index 3628f7cfb178..9b77992c4888 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -174,11 +174,15 @@ extern void		    audit_log_format(struct audit_buffer *ab,
                                              const char *fmt, ...)
                             __attribute__((format(printf,2,3)));
 extern void                 audit_log_end(struct audit_buffer *ab);
+extern void                 audit_log_hex(struct audit_buffer *ab,
+                                          const unsigned char *buf,
+                                          size_t len);
+extern void                 audit_log_untrustedstring(struct audit_buffer *ab,
+                                                      const char *string);
 extern void                 audit_log_d_path(struct audit_buffer *ab,
                                              const char *prefix,
                                              struct dentry *dentry,
                                              struct vfsmount *vfsmnt);
-
                                 /* Private API (for auditsc.c only) */
 extern void                 audit_send_reply(int pid, int seq, int type,
                                              int done, int multi,
@@ -190,6 +194,8 @@ extern void		    audit_log_lost(const char *message);
 #define audit_log_vformat(b,f,a) do { ; } while (0)
 #define audit_log_format(b,f,...) do { ; } while (0)
 #define audit_log_end(b) do { ; } while (0)
+#define audit_log_hex(a,b,l) do { ; } while (0)
+#define audit_log_untrustedstring(a,s) do { ; } while (0)
 #define audit_log_d_path(b,p,d,v) do { ; } while (0)
 #endif
 #endif
diff --git a/kernel/audit.c b/kernel/audit.c
index 0f84dd7af2c8..dca7b99615d2 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -720,6 +720,29 @@ void audit_log_format(struct audit_buffer *ab, const char *fmt, ...)
         va_end(args);
 }
 
+void audit_log_hex(struct audit_buffer *ab, const unsigned char *buf, size_t len)
+{
+        int i;
+
+        for (i=0; i<len; i++)
+                audit_log_format(ab, "%02x", buf[i]);
+}
+
+void audit_log_untrustedstring(struct audit_buffer *ab, const char *string)
+{
+        const char *p = string;
+
+        while (*p) {
+                if (*p == '"' || *p == ' ' || *p < 0x20 || *p > 0x7f) {
+                        audit_log_hex(ab, string, strlen(string));
+                        return;
+                }
+                p++;
+        }
+        audit_log_format(ab, "\"%s\"", string);
+}
+
+
 /* This is a helper-function to print the d_path without using a static
  * buffer or allocating another buffer in addition to the one in
  * audit_buffer. */
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 6f1931381bc9..00e87ffff13b 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -696,9 +696,10 @@ static void audit_log_exit(struct audit_context *context)
                 if (!ab)
                         continue; /* audit_panic has been called */
                 audit_log_format(ab, "item=%d", i);
-                if (context->names[i].name)
-                        audit_log_format(ab, " name=%s",
-                                         context->names[i].name);
+                if (context->names[i].name) {
+                        audit_log_format(ab, " name=");
+                        audit_log_untrustedstring(ab, context->names[i].name);
+                }
                 if (context->names[i].ino != (unsigned long)-1)
                         audit_log_format(ab, " inode=%lu dev=%02x:%02x mode=%#o"
                                              " uid=%d gid=%d rdev=%02x:%02x",