fix OOB reads in Xbyte_memmem

Reported by Leah Neukirchen.

diff --git a/src/string/memmem.c b/src/string/memmem.c
index 4be6a310a7618e791615fcb8543eb2f23d47370b..54a66e466aac1dce4e7312cb30206d4f52d6ab4c 100644 (file)
--- a/src/string/memmem.c
+++ b/src/string/memmem.c
@@ -5,27 +5,27 @@
 static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
        uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
-       for (h++, k--; k; k--, hw = hw<<8 | *++h)
-               if (hw == nw) return (char *)h-1;
-       return 0;
+       for (h+=2, k-=2; k; k--, hw = hw<<8 | *h++)
+               if (hw == nw) return (char *)h-2;
+       return hw == nw ? (char *)h-2 : 0;
 }
 
 static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
        uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
        uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
-       for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
-               if (hw == nw) return (char *)h-2;
-       return 0;
+       for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
+               if (hw == nw) return (char *)h-3;
+       return hw == nw ? (char *)h-3 : 0;
 }
 
 static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
        uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
        uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
-       for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
-               if (hw == nw) return (char *)h-3;
-       return 0;
+       for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
+               if (hw == nw) return (char *)h-4;
+       return hw == nw ? (char *)h-4 : 0;
 }
 
 #define MAX(a,b) ((a)>(b)?(a):(b))