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mount-encrypted: fix some minor security TODOs

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Force mode of created key file to 0600, and make sure there is enough
room in the decryption buffer for any possible change to the decryption
algo.

BUG=None
TEST=alex build, manual testing

Change-Id: I89dceec22683ff66b5e1f61a63f14a1db1c4e2ee
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28892
Reviewed-by: Elly Jones <ellyjones@chromium.org>
This commit is contained in:
Kees Cook
2012-07-31 18:14:18 -07:00
committed by Gerrit
parent af44dce1e8
commit a8fae24b25
1 changed files with 6 additions and 3 deletions
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9
utility/mount-helpers.c
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@@ -553,7 +553,7 @@ char *keyfile_read(const char *keyfile, uint8_t *system_key)
g_error_free(error);
goto out;
}
plain = malloc(length);
plain = malloc(length + EVP_CIPHER_block_size(algo));
if (!plain) {
PERROR("malloc");
goto free_cipher;
@@ -565,7 +565,6 @@ char *keyfile_read(const char *keyfile, uint8_t *system_key)
SSL_ERROR("EVP_DecryptInit");
goto free_plain;
}
/* TODO(keescook): this is a heap overflow -- file size not checked. */
if (!EVP_DecryptUpdate(&ctx, plain, &plain_length, cipher, length)) {
SSL_ERROR("EVP_DecryptUpdate");
goto free_ctx;
@@ -607,8 +606,12 @@ int keyfile_write(const char *keyfile, uint8_t *system_key, char *string)
GError *error = NULL;
EVP_CIPHER_CTX ctx;
const EVP_CIPHER *algo = EVP_aes_256_cbc();
mode_t mask;
DEBUG("Staring to process keyfile %s", keyfile);
/* Have key file be read/write only by root user. */
mask = umask(0077);
if (EVP_CIPHER_key_length(algo) != DIGEST_LENGTH) {
ERROR("cipher key size mismatch (got %d, want %d)",
EVP_CIPHER_key_length(algo), DIGEST_LENGTH);
@@ -659,7 +662,6 @@ int keyfile_write(const char *keyfile, uint8_t *system_key, char *string)
length = cipher_length + final_len;
DEBUG("Writing %zu bytes to %s", length, keyfile);
/* TODO(keescook): replace this with a mode-400 writer. */
if (!g_file_set_contents(keyfile, (gchar *)cipher, length, &error)) {
ERROR("Unable to write %s: %s", keyfile, error->message);
g_error_free(error);
@@ -673,6 +675,7 @@ free_ctx:
free_cipher:
free(cipher);
out:
umask(mask);
DEBUG("keyfile write rc:%d", rc);
return rc;
}