[PATCH 1/2] audit: fix NUL handling in untrusted strings
From: Miloslav Trmac <mitr(a)redhat.com>
audit_string_contains_control() stops checking at the first NUL byte.
If audit_string_contains_control() returns FALSE,
audit_log_n_untrustedstring() submits the complete string - including
the NUL byte and all following bytes, up to the specified maximum length
- to audit_log_n_string(), which copies the data unchanged into the
audit record.
The audit record can thus contain a NUL byte (and some unchecked data
after that). Because the user-space audit daemon treats audit records
as NUL-terminated strings, an untrusted string that is shorter than the
specified maximum length effectively terminates the audit record.
This patch modifies audit_log_n_untrustedstring() to only log the data
before the first NUL byte, if any.
Signed-off-by: Miloslav Trmac <mitr(a)redhat.com>
---
kernel/audit.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index 4414e93..03b6397 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1362,6 +1362,12 @@ void audit_log_n_string(struct audit_buffer *ab, const char
*string,
skb_put(skb, slen + 2); /* don't include null terminator */
}
+static inline int
+audit_is_control_character(unsigned char c)
+{
+ return c == '"' || c < 0x21 || c > 0x7E;
+}
+
/**
* audit_string_contains_control - does a string need to be logged in hex
* @string: string to be checked
@@ -1371,7 +1377,7 @@ int audit_string_contains_control(const char *string, size_t len)
{
const unsigned char *p;
for (p = string; p < (const unsigned char *)string + len && *p; p++) {
- if (*p == '"' || *p < 0x21 || *p > 0x7e)
+ if (audit_is_control_character(*p))
return 1;
}
return 0;
@@ -1394,10 +1400,15 @@ int audit_string_contains_control(const char *string, size_t len)
void audit_log_n_untrustedstring(struct audit_buffer *ab, const char *string,
size_t len)
{
- if (audit_string_contains_control(string, len))
- audit_log_n_hex(ab, string, len);
- else
- audit_log_n_string(ab, string, len);
+ const unsigned char *p;
+
+ for (p = string; p < (const unsigned char *)string + len && *p; p++) {
+ if (audit_is_control_character(*p)) {
+ audit_log_n_hex(ab, string, len);
+ return;
+ }
+ }
+ audit_log_n_string(ab, string, p - (const unsigned char *)string);
}
/**