Fix debuggerd (native crash dump).

Change 44659e90f (6cc4923087 in AOSP) introduced walking
both the symbol table and dynamic symbol table. The problem
is that it was dereferencing values whether or not the two tables
were both present, which could wind up reading from invalid memory.
The read from a bad address would cause debuggerd itself to crash,
which isn't handled.

Change-Id: Ie936f660018b1980dee5b6ed669588db861f1a79

1 files changed, 19 insertions, 10 deletions

diff --git a/debuggerd/symbol_table.c b/debuggerd/symbol_table.c
index e76df33..fd008fe 100644
--- a/debuggerd/symbol_table.c
+++ b/debuggerd/symbol_table.c
@@ -94,17 +94,26 @@ struct symbol_table *symbol_table_create(const char *filename)
     table->name = strdup(filename);
     table->num_symbols = 0;
 
-    Elf32_Sym *dynsyms = (Elf32_Sym*)(base + shdr[dynsym_idx].sh_offset);
-    Elf32_Sym *syms = (Elf32_Sym*)(base + shdr[sym_idx].sh_offset);
+    Elf32_Sym *dynsyms = NULL;
+    Elf32_Sym *syms = NULL;
+    int dynnumsyms = 0;
+    int numsyms = 0;
+    char *dynstr = NULL;
+    char *str = NULL;
 
-    int dynnumsyms = shdr[dynsym_idx].sh_size / shdr[dynsym_idx].sh_entsize;
-    int numsyms = shdr[sym_idx].sh_size / shdr[sym_idx].sh_entsize;
-
-    int dynstr_idx = shdr[dynsym_idx].sh_link;
-    int str_idx = shdr[sym_idx].sh_link;
+    if (dynsym_idx != -1) {
+        dynsyms = (Elf32_Sym*)(base + shdr[dynsym_idx].sh_offset);
+        dynnumsyms = shdr[dynsym_idx].sh_size / shdr[dynsym_idx].sh_entsize;
+        int dynstr_idx = shdr[dynsym_idx].sh_link;
+        dynstr = base + shdr[dynstr_idx].sh_offset;
+    }
 
-    char *dynstr = base + shdr[dynstr_idx].sh_offset;
-    char *str = base + shdr[str_idx].sh_offset;
+    if (sym_idx != -1) {
+        syms = (Elf32_Sym*)(base + shdr[sym_idx].sh_offset);
+        numsyms = shdr[sym_idx].sh_size / shdr[sym_idx].sh_entsize;
+        int str_idx = shdr[sym_idx].sh_link;
+        str = base + shdr[str_idx].sh_offset;
+    }
 
     int symbol_count = 0;
     int dynsymbol_count = 0;
@@ -134,7 +143,7 @@ struct symbol_table *symbol_table_create(const char *filename)
     }
 
     // Now, create an entry in our symbol table structure for each symbol...
-    table->num_symbols += symbol_count + dynsymbol_count;;
+    table->num_symbols += symbol_count + dynsymbol_count;
     table->symbols = malloc(table->num_symbols * sizeof(struct symbol));
     if(!table->symbols) {
         free(table);