[PATCH v3 1/7] ima-evm-utils: Fix hash buffer overflow in verify_evm and hmac_evm

[Vitaly Chikunov <vt@xxxxxxxxxxxx>]

Commit ae1319eeabd6 ("Remove hardcoding of SHA1 in EVM signatures")
introduces overflow of 20 byte buffer on the stack while calculating
hash. Also, invalid hash length is passed to the underlying verification
function in verify_evm. This prevents any non-SHA1 hashes from being
properly validated using evmctl.

Fixes: ae1319eeabd6 ("Remove hardcoding of SHA1 in EVM signatures")
Signed-off-by: Vitaly Chikunov <vt@xxxxxxxxxxxx>
---
Changes since v1:
- Fix similar issue in hmac_evm
Changes since v2:
- No changes.

 src/evmctl.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/evmctl.c b/src/evmctl.c
index 1b46d58..f8035da 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -55,6 +55,7 @@
 #include <keyutils.h>
 #include <ctype.h>
 #include <termios.h>
+#include <assert.h>
 
 #include <openssl/sha.h>
 #include <openssl/pem.h>
@@ -760,13 +761,15 @@ static int cmd_sign_evm(struct command *cmd)
 
 static int verify_evm(const char *file)
 {
-	unsigned char hash[20];
+	unsigned char hash[64];
 	unsigned char sig[1024];
+	int mdlen;
 	int len;
 
-	len = calc_evm_hash(file, hash);
-	if (len <= 1)
-		return len;
+	mdlen = calc_evm_hash(file, hash);
+	assert(mdlen <= sizeof(hash));
+	if (mdlen <= 1)
+		return mdlen;
 
 	len = lgetxattr(file, "security.evm", sig, sizeof(sig));
 	if (len < 0) {
@@ -779,7 +782,7 @@ static int verify_evm(const char *file)
 		return -1;
 	}
 
-	return verify_hash(file, hash, sizeof(hash), sig + 1, len - 1);
+	return verify_hash(file, hash, mdlen, sig + 1, len - 1);
 }
 
 static int cmd_verify_evm(struct command *cmd)
@@ -1135,11 +1138,12 @@ out:
 
 static int hmac_evm(const char *file, const char *key)
 {
-	unsigned char hash[20];
+	unsigned char hash[64];
 	unsigned char sig[1024];
 	int len, err;
 
 	len = calc_evm_hmac(file, key, hash);
+	assert(len <= sizeof(hash));
 	if (len <= 1)
 		return len;
 
-- 
2.11.0