libmach: respect symbol table boundaries

Since fp->symsz includes the size of the header
in the new symbol table format, we were reading
past the end and decoding a few garbage symbols
from data in the pc/line table.

R=rsc, r
CC=golang-dev
https://golang.org/cl/7993043

diff --git a/src/libmach/sym.c b/src/libmach/sym.c
index 120328d09a8d055457ed5dbdbeebf7b566174b77..28c80d64131890b2fd00527de8654050795a309f 100644 (file)
--- a/src/libmach/sym.c
+++ b/src/libmach/sym.c
@@ -109,7 +109,7 @@ int
 syminit(int fd, Fhdr *fp)
 {
        Sym *p;
-       int32 i, l, size;
+       int32 i, l, size, symsz;
        vlong vl;
        Biobuf b;
        int svalsz, newformat, shift;
@@ -138,6 +138,7 @@ syminit(int fd, Fhdr *fp)
        memset(buf, 0, sizeof buf);
        Bread(&b, buf, sizeof buf);
        newformat = 0;
+       symsz = fp->symsz;
        if(memcmp(buf, "\xfd\xff\xff\xff\x00\x00\x00", 7) == 0) {
                swav = leswav;
                swal = leswal;
@@ -151,6 +152,7 @@ syminit(int fd, Fhdr *fp)
                swav = leswav;
                swal = leswal;
                Bseek(&b, fp->symoff+6, 0);
+               symsz -= 6;
        } else {
                Bseek(&b, fp->symoff, 0);
        }
@@ -161,11 +163,12 @@ syminit(int fd, Fhdr *fp)
                        werrstr("invalid word size %d bytes", svalsz);
                        return -1;
                }
+               symsz -= 8;
        }
 
        nsym = 0;
        size = 0;
-       for(p = symbols; size < fp->symsz; p++, nsym++) {
+       for(p = symbols; size < symsz; p++, nsym++) {
                if(newformat) {
                        // Go 1.1 format. See comment at top of ../pkg/runtime/symtab.c.
                        if(Bread(&b, &c, 1) != 1)