[PATCH v5 6/6] module: Move duplicate mod_check_sig users code to mod_parse_sig
Michal Suchanek
msuchanek at suse.de
Tue Jan 11 11:37:48 UTC 2022
Multiple users of mod_check_sig check for the marker, then call
mod_check_sig, extract signature length, and remove the signature.
Put this code in one place together with mod_check_sig.
This changes the error from ENOENT to ENODATA for ima_read_modsig in the
case the signature marker is missing.
This also changes the buffer length in ima_read_modsig from size_t to
unsigned long. This reduces the possible value range on 32bit but the
length refers to kernel in-memory buffer which cannot be longer than
ULONG_MAX.
Also change mod_check_sig to unsigned long while at it.
Signed-off-by: Michal Suchanek <msuchanek at suse.de>
---
v3: - Philipp Rudo <prudo at redhat.com>: Update the commit with note about
change of raturn value
- Preserve the EBADMSG error code while moving code araound
v4: - remove unused variable ms in module_signing.c
- note about buffer length
v5: - also change the functions in module_signature.c to unsigned long
---
include/linux/module_signature.h | 4 +-
kernel/module_signature.c | 58 ++++++++++++++++++++++++++++-
kernel/module_signing.c | 27 ++------------
security/integrity/ima/ima_modsig.c | 22 ++---------
4 files changed, 66 insertions(+), 45 deletions(-)
diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h
index 7eb4b00381ac..e5fb157c085c 100644
--- a/include/linux/module_signature.h
+++ b/include/linux/module_signature.h
@@ -40,7 +40,9 @@ struct module_signature {
__be32 sig_len; /* Length of signature data */
};
-int mod_check_sig(const struct module_signature *ms, size_t file_len,
+int mod_check_sig(const struct module_signature *ms, unsigned long file_len,
+ const char *name);
+int mod_parse_sig(const void *data, unsigned long *len, unsigned long *sig_len,
const char *name);
#endif /* _LINUX_MODULE_SIGNATURE_H */
diff --git a/kernel/module_signature.c b/kernel/module_signature.c
index 00132d12487c..4a36405ecd08 100644
--- a/kernel/module_signature.c
+++ b/kernel/module_signature.c
@@ -8,17 +8,39 @@
#include <linux/errno.h>
#include <linux/printk.h>
+#include <linux/string.h>
#include <linux/module_signature.h>
#include <asm/byteorder.h>
+/**
+ * mod_check_sig_marker - check that the given data has signature marker at the end
+ *
+ * @data: Data with appended signature
+ * @len: Length of data. Signature marker length is subtracted on success.
+ */
+static inline int mod_check_sig_marker(const void *data, unsigned long *len)
+{
+ const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+
+ if (markerlen > *len)
+ return -ENODATA;
+
+ if (memcmp(data + *len - markerlen, MODULE_SIG_STRING,
+ markerlen))
+ return -ENODATA;
+
+ *len -= markerlen;
+ return 0;
+}
+
/**
* mod_check_sig - check that the given signature is sane
*
* @ms: Signature to check.
- * @file_len: Size of the file to which @ms is appended.
+ * @file_len: Size of the file to which @ms is appended (without the marker).
* @name: What is being checked. Used for error messages.
*/
-int mod_check_sig(const struct module_signature *ms, size_t file_len,
+int mod_check_sig(const struct module_signature *ms, unsigned long file_len,
const char *name)
{
if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
@@ -44,3 +66,35 @@ int mod_check_sig(const struct module_signature *ms, size_t file_len,
return 0;
}
+
+/**
+ * mod_parse_sig - check that the given signature is sane and determine signature length
+ *
+ * @data: Data with appended signature.
+ * @len: Length of data. Signature and marker length is subtracted on success.
+ * @sig_len: Length of signature. Filled on success.
+ * @name: What is being checked. Used for error messages.
+ */
+int mod_parse_sig(const void *data, unsigned long *len, unsigned long *sig_len, const char *name)
+{
+ const struct module_signature *sig;
+ int rc;
+
+ rc = mod_check_sig_marker(data, len);
+ if (rc)
+ return rc;
+
+ if (*len < sizeof(*sig))
+ return -EBADMSG;
+
+ sig = data + (*len - sizeof(*sig));
+
+ rc = mod_check_sig(sig, *len, name);
+ if (rc)
+ return rc;
+
+ *sig_len = be32_to_cpu(sig->sig_len);
+ *len -= *sig_len + sizeof(*sig);
+
+ return 0;
+}
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index 20857d2a15ca..1d4cb03cce21 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -25,35 +25,16 @@ int verify_appended_signature(const void *data, unsigned long *len,
struct key *trusted_keys,
enum key_being_used_for purpose)
{
- const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
- struct module_signature *ms;
- unsigned long sig_len, modlen = *len;
+ unsigned long sig_len;
int ret;
- pr_devel("==>%s %s(,%lu)\n", __func__, key_being_used_for[purpose], modlen);
+ pr_devel("==>%s %s(,%lu)\n", __func__, key_being_used_for[purpose], *len);
- if (markerlen > modlen)
- return -ENODATA;
-
- if (memcmp(data + modlen - markerlen, MODULE_SIG_STRING,
- markerlen))
- return -ENODATA;
- modlen -= markerlen;
-
- if (modlen <= sizeof(*ms))
- return -EBADMSG;
-
- ms = data + modlen - sizeof(*ms);
-
- ret = mod_check_sig(ms, modlen, key_being_used_for[purpose]);
+ ret = mod_parse_sig(data, len, &sig_len, key_being_used_for[purpose]);
if (ret)
return ret;
- sig_len = be32_to_cpu(ms->sig_len);
- modlen -= sig_len + sizeof(*ms);
- *len = modlen;
-
- return verify_pkcs7_signature(data, modlen, data + modlen, sig_len,
+ return verify_pkcs7_signature(data, *len, data + *len, sig_len,
trusted_keys,
purpose,
NULL, NULL);
diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index fb25723c65bc..b40c8fdf6139 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -37,33 +37,17 @@ struct modsig {
*
* Return: 0 on success, error code otherwise.
*/
-int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
+int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t len,
struct modsig **modsig)
{
- const size_t marker_len = strlen(MODULE_SIG_STRING);
- const struct module_signature *sig;
struct modsig *hdr;
- size_t sig_len;
- const void *p;
+ unsigned long sig_len, buf_len = len;
int rc;
- if (buf_len <= marker_len + sizeof(*sig))
- return -ENOENT;
-
- p = buf + buf_len - marker_len;
- if (memcmp(p, MODULE_SIG_STRING, marker_len))
- return -ENOENT;
-
- buf_len -= marker_len;
- sig = (const struct module_signature *)(p - sizeof(*sig));
-
- rc = mod_check_sig(sig, buf_len, func_tokens[func]);
+ rc = mod_parse_sig(buf, &buf_len, &sig_len, func_tokens[func]);
if (rc)
return rc;
- sig_len = be32_to_cpu(sig->sig_len);
- buf_len -= sig_len + sizeof(*sig);
-
/* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
if (!hdr)
--
2.31.1
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