[exim-cvs] SECURITY: Avoid memory corruption in dkim handlin…

Gitweb: https://git.exim.org/exim.git/commitdiff/20586bdc24045da63928cbdaace2f036e3c80bd5

Commit:     20586bdc24045da63928cbdaace2f036e3c80bd5
Parent:     d97d073f5dc62d2a7352c5cf6506a771876d7f11
Author:     Heiko Schlittermann (HS12-RIPE) <hs@???>
AuthorDate: Wed Nov 25 23:19:57 2020 +0100
Committer:  Heiko Schlittermann (HS12-RIPE) <hs@???>
CommitDate: Thu May 27 21:30:38 2021 +0200

    SECURITY: Avoid memory corruption in dkim handling

    Credits: Qualys

        6/ In src/pdkim/pdkim.c, pdkim_update_ctx_bodyhash() is sometimes called
        with a global orig_data and hence canon_data, and the following line can
        therefore modify data that should be constant:

         773   canon_data->len = b->bodylength - b->signed_body_bytes;

        For example, the following proof of concept sets lineending.len to 0
        (this should not be possible):

        (sleep 10; echo 'EHLO test'; sleep 3; echo 'MAIL FROM:<>'; sleep 3; echo 'RCPT TO:postmaster'; sleep 3; echo 'DATA'; date >&2; sleep 30; printf 'DKIM-Signature:a=rsa-sha1;c=simple/simple;l=0\r\n\r\n\r\nXXX\r\n.\r\n'; sleep 30) | nc -n -v 192.168.56.102 25

        (gdb) print lineending
        $1 = {data = 0x55e18035b2ad "\r\n", len = 2}
        (gdb) print &lineending.len
        $3 = (size_t *) 0x55e180385948 <lineending+8>
        (gdb) watch *(size_t *) 0x55e180385948

        Hardware watchpoint 1: *(size_t *) 0x55e180385948
        Old value = 2
        New value = 0
        (gdb) print lineending
        $5 = {data = 0x55e18035b2ad "\r\n", len = 0}

    (cherry picked from commit ea850e27714ccda2090d781ebe89b410bc38c2c6)
    (cherry picked from commit 4e784efa28b25683c81a857b464777df593cabee)
---
 src/src/pdkim/pdkim.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/src/pdkim/pdkim.c b/src/src/pdkim/pdkim.c
index b4301b5..82dab3d 100644
--- a/src/src/pdkim/pdkim.c
+++ b/src/src/pdkim/pdkim.c
@@ -722,7 +722,9 @@ If we have to relax the data for this sig, return our copy of it. */
static blob *
pdkim_update_ctx_bodyhash(pdkim_bodyhash * b, blob * orig_data, blob * relaxed_data)
{
-blob * canon_data = orig_data;
+const blob const * canon_data = orig_data;
+size_t len;
+
/* Defaults to simple canon (no further treatment necessary) */

 if (b->canon_method == PDKIM_CANON_RELAXED)
@@ -770,13 +772,13 @@ if (b->canon_method == PDKIM_CANON_RELAXED)
 if (  b->bodylength >= 0
    && b->signed_body_bytes + (unsigned long)canon_data->len > b->bodylength
    )
-  canon_data->len = b->bodylength - b->signed_body_bytes;
+  len = b->bodylength - b->signed_body_bytes;

-if (canon_data->len > 0)
+if (len > 0)
{
- exim_sha_update(&b->body_hash_ctx, CUS canon_data->data, canon_data->len);
- b->signed_body_bytes += canon_data->len;
- DEBUG(D_acl) pdkim_quoteprint(canon_data->data, canon_data->len);
+ exim_sha_update(&b->body_hash_ctx, CUS canon_data->data, len);
+ b->signed_body_bytes += len;
+ DEBUG(D_acl) pdkim_quoteprint(canon_data->data, len);
}

return relaxed_data;