verify_pefile: relax wrapper length check

The PE Format Specification (section "The Attribute Certificate Table
(Image Only)") states that `dwLength` is to be rounded up to 8-byte
alignment when used for traversal.  Therefore, the field is not required
to be an 8-byte multiple in the first place.

Accordingly, pesign has not performed this alignment since version
0.110.  This causes kexec failure on pesign'd binaries with "PEFILE:
Signature wrapper len wrong".  Update the comment and relax the check.

Signed-off-by: Robbie Harwood <rharwood@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko@kernel.org>
cc: Eric Biederman <ebiederm@xmission.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: keyrings@vger.kernel.org
cc: linux-crypto@vger.kernel.org
cc: kexec@lists.infradead.org
Link: https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#the-attribute-certificate-table-image-only
Link: https://github.com/rhboot/pesign
Link: https://lore.kernel.org/r/20230220171254.592347-2-rharwood@redhat.com/

diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
index 7553ab18db898ffd887b7a7c487506780eb409e6..fe1bb374239d770ed4cdf6f4783af098fc8e1f7c 100644 (file)
--- a/crypto/asymmetric_keys/verify_pefile.c
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -135,11 +135,15 @@ static int pefile_strip_sig_wrapper(const void *pebuf,
        pr_debug("sig wrapper = { %x, %x, %x }\n",
                 wrapper.length, wrapper.revision, wrapper.cert_type);
 
-       /* Both pesign and sbsign round up the length of certificate table
-        * (in optional header data directories) to 8 byte alignment.
+       /* sbsign rounds up the length of certificate table (in optional
+        * header data directories) to 8 byte alignment.  However, the PE
+        * specification states that while entries are 8-byte aligned, this is
+        * not included in their length, and as a result, pesign has not
+        * rounded up since 0.110.
         */
-       if (round_up(wrapper.length, 8) != ctx->sig_len) {
-               pr_debug("Signature wrapper len wrong\n");
+       if (wrapper.length > ctx->sig_len) {
+               pr_debug("Signature wrapper bigger than sig len (%x > %x)\n",
+                        ctx->sig_len, wrapper.length);
                return -ELIBBAD;
        }
        if (wrapper.revision != WIN_CERT_REVISION_2_0) {