From 00596c167335912314757fd6efc4b46c9c3c029a Mon Sep 17 00:00:00 2001
From: Iaroslav Gridin <iaroslav.gridin@tuni.fi>
Date: Thu, 20 Apr 2023 13:13:37 +0000
Subject: Bug 1784163 - Fix reading raw negative numbers
 r=nss-reviewers,nkulatova,mt

set sign after adding digits

Differential Revision: https://phabricator.services.mozilla.com/D154315
---
 cmd/mpitests/mpi-test.c | 16 ++++++++++++++++
 lib/freebl/mpi/mpi.c    | 12 ++++++------
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/cmd/mpitests/mpi-test.c b/cmd/mpitests/mpi-test.c
index cc045a17c..af4633aa9 100644
--- a/cmd/mpitests/mpi-test.c
+++ b/cmd/mpitests/mpi-test.c
@@ -2011,9 +2011,11 @@ test_raw(void)
 {
     int len, out = 0;
     mp_int a;
+    mp_int b;
     char *buf;
 
     mp_init(&a);
+    mp_init(&b);
     mp_read_radix(&a, mp4, 16);
 
     len = mp_raw_size(&a);
@@ -2032,8 +2034,22 @@ test_raw(void)
         out = 1;
     }
 
+    // read the binary output back and compare with the original number
+    memcpy(buf, b_mp4, sizeof(b_mp4));
+    mp_err read_err = mp_read_raw(&b, buf, sizeof(b_mp4));
+    if (read_err != MP_OKAY) {
+        reason("error: reading raw mp_int failed: %d\n", read_err);
+        out = 1;
+    }
+
+    if (mp_cmp(&a, &b) != 0) {
+        reason("error: test_raw: mp_int from read_raw does not match the original number\n");
+        out = 1;
+    }
+
     free(buf);
     mp_clear(&a);
+    mp_clear(&b);
 
     return out;
 }
diff --git a/lib/freebl/mpi/mpi.c b/lib/freebl/mpi/mpi.c
index bc4c148d6..2e6cd8466 100644
--- a/lib/freebl/mpi/mpi.c
+++ b/lib/freebl/mpi/mpi.c
@@ -2520,12 +2520,6 @@ mp_read_raw(mp_int *mp, char *str, int len)
 
     mp_zero(mp);
 
-    /* Get sign from first byte */
-    if (ustr[0])
-        SIGN(mp) = NEG;
-    else
-        SIGN(mp) = ZPOS;
-
     /* Read the rest of the digits */
     for (ix = 1; ix < len; ix++) {
         if ((res = mp_mul_d(mp, 256, mp)) != MP_OKAY)
@@ -2534,6 +2528,12 @@ mp_read_raw(mp_int *mp, char *str, int len)
             return res;
     }
 
+    /* Get sign from first byte */
+    if (ustr[0])
+        SIGN(mp) = NEG;
+    else
+        SIGN(mp) = ZPOS;
+
     return MP_OKAY;
 
 } /* end mp_read_raw() */
-- 
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