script: Avoid a use-after-free when redefining a function during execution
Defining a new function with the same name as a previously defined function causes the grub_script and associated resources for the previous function to be freed. If the previous function is currently executing when a function with the same name is defined, this results in use-after-frees when processing subsequent commands in the original function. Instead, reject a new function definition if it has the same name as a previously defined function, and that function is currently being executed. Although a behavioural change, this should be backwards compatible with existing configurations because they can't be dependent on the current behaviour without being broken. Fixes: CVE-2020-15706 Signed-off-by: Chris Coulson <chris.coulson@canonical.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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4 changed files with 19 additions and 4 deletions
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@ -838,7 +838,9 @@ grub_script_function_call (grub_script_function_t func, int argc, char **args)
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old_scope = scope;
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scope = &new_scope;
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func->executing++;
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ret = grub_script_execute (func->func);
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func->executing--;
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function_return = 0;
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active_loops = loops;
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@ -34,6 +34,7 @@ grub_script_function_create (struct grub_script_arg *functionname_arg,
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func = (grub_script_function_t) grub_malloc (sizeof (*func));
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if (! func)
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return 0;
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func->executing = 0;
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func->name = grub_strdup (functionname_arg->str);
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if (! func->name)
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@ -60,10 +61,19 @@ grub_script_function_create (struct grub_script_arg *functionname_arg,
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grub_script_function_t q;
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q = *p;
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grub_script_free (q->func);
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q->func = cmd;
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grub_free (func);
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func = q;
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if (q->executing > 0)
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{
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grub_error (GRUB_ERR_BAD_ARGUMENT,
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N_("attempt to redefine a function being executed"));
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func = NULL;
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}
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else
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{
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grub_script_free (q->func);
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q->func = cmd;
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func = q;
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}
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}
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else
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{
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@ -289,7 +289,8 @@ function: "function" "name"
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grub_script_mem_free (state->func_mem);
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else {
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script->children = state->scripts;
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grub_script_function_create ($2, script);
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if (!grub_script_function_create ($2, script))
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grub_script_free (script);
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}
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state->scripts = $<scripts>3;
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@ -361,6 +361,8 @@ struct grub_script_function
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/* The next element. */
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struct grub_script_function *next;
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unsigned executing;
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};
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typedef struct grub_script_function *grub_script_function_t;
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