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From 31106a073882656a2a5ab56c4ce2847e9a334c3c Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Wed, 28 Sep 2016 10:15:34 +0200
Subject: [PATCH] aprintf: detect wrap-around when growing allocation

On 32bit systems we could otherwise wrap around after 2GB and allocate 0
bytes and crash.

CVE-2016-8618

Bug: https://curl.haxx.se/docs/adv_20161102D.html
Reported-by: Cure53
---
 lib/mprintf.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/mprintf.c b/lib/mprintf.c
index dbedeaa..2c88aa8 100644
--- a/lib/mprintf.c
+++ b/lib/mprintf.c
@@ -1034,20 +1034,23 @@ static int alloc_addbyter(int output, FILE *data)
     }
     infop->alloc = 32;
     infop->len =0;
   }
   else if(infop->len+1 >= infop->alloc) {
-    char *newptr;
+    char *newptr = NULL;
+    size_t newsize = infop->alloc*2;
 
-    newptr = realloc(infop->buffer, infop->alloc*2);
+    /* detect wrap-around or other overflow problems */
+    if(newsize > infop->alloc)
+      newptr = realloc(infop->buffer, newsize);
 
     if(!newptr) {
       infop->fail = 1;
       return -1; /* fail */
     }
     infop->buffer = newptr;
-    infop->alloc *= 2;
+    infop->alloc = newsize;
   }
 
   infop->buffer[ infop->len ] = outc;
 
   infop->len++;
-- 
2.9.3