net/http: Fix OOB write for split http headers

GRUB has special code for handling an http header that is split
across two packets.

The code tracks the end of line by looking for a "\n" byte. The
code for split headers has always advanced the pointer just past the
end of the line, whereas the code that handles unsplit headers does
not advance the pointer. This extra advance causes the length to be
one greater, which breaks an assumption in parse_line(), leading to
it writing a NUL byte one byte past the end of the buffer where we
reconstruct the line from the two packets.

It's conceivable that an attacker controlled set of packets could
cause this to zero out the first byte of the "next" pointer of the
grub_mm_region structure following the current_line buffer.

Do not advance the pointer in the split header case.

Fixes: CVE-2022-28734
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/net/http.c b/grub-core/net/http.c
index f8d7bf0cd466cab43e2dd079e28d0c6421a0cb10..33a0a28c48b0eb6163e5a25bb853f7124b766e11 100644 (file)
--- a/grub-core/net/http.c
+++ b/grub-core/net/http.c
@@ -190,9 +190,7 @@ http_receive (grub_net_tcp_socket_t sock __attribute__ ((unused)),
          int have_line = 1;
          char *t;
          ptr = grub_memchr (nb->data, '\n', nb->tail - nb->data);
-         if (ptr)
-           ptr++;
-         else
+         if (ptr == NULL)
            {
              have_line = 0;
              ptr = (char *) nb->tail;