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From c65fc7e75b7b7e880d90766057040011701e97f4 Mon Sep 17 00:00:00 2001
From: Chris Coulson <chris.coulson@canonical.com>
Date: Fri, 10 Jul 2020 14:41:45 +0100
Subject: [PATCH 8/9] 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>
Upstream-Status: Backport
CVE: CVE-2020-15706
Reference to upstream patch:
https://git.savannah.gnu.org/cgit/grub.git/commit/?id=426f57383d647406ae9c628c472059c27cd6e040
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>
---
grub-core/script/execute.c | 2 ++
grub-core/script/function.c | 16 +++++++++++++---
grub-core/script/parser.y | 3 ++-
include/grub/script_sh.h | 2 ++
4 files changed, 19 insertions(+), 4 deletions(-)
diff --git a/grub-core/script/execute.c b/grub-core/script/execute.c
index c8d6806..7e028e1 100644
--- a/grub-core/script/execute.c
+++ b/grub-core/script/execute.c
@@ -838,7 +838,9 @@ grub_script_function_call (grub_script_function_t func, int argc, char **args)
old_scope = scope;
scope = &new_scope;
+ func->executing++;
ret = grub_script_execute (func->func);
+ func->executing--;
function_return = 0;
active_loops = loops;
diff --git a/grub-core/script/function.c b/grub-core/script/function.c
index d36655e..3aad04b 100644
--- a/grub-core/script/function.c
+++ b/grub-core/script/function.c
@@ -34,6 +34,7 @@ grub_script_function_create (struct grub_script_arg *functionname_arg,
func = (grub_script_function_t) grub_malloc (sizeof (*func));
if (! func)
return 0;
+ func->executing = 0;
func->name = grub_strdup (functionname_arg->str);
if (! func->name)
@@ -60,10 +61,19 @@ grub_script_function_create (struct grub_script_arg *functionname_arg,
grub_script_function_t q;
q = *p;
- grub_script_free (q->func);
- q->func = cmd;
grub_free (func);
- func = q;
+ if (q->executing > 0)
+ {
+ grub_error (GRUB_ERR_BAD_ARGUMENT,
+ N_("attempt to redefine a function being executed"));
+ func = NULL;
+ }
+ else
+ {
+ grub_script_free (q->func);
+ q->func = cmd;
+ func = q;
+ }
}
else
{
diff --git a/grub-core/script/parser.y b/grub-core/script/parser.y
index 4f0ab83..f80b86b 100644
--- a/grub-core/script/parser.y
+++ b/grub-core/script/parser.y
@@ -289,7 +289,8 @@ function: "function" "name"
grub_script_mem_free (state->func_mem);
else {
script->children = state->scripts;
- grub_script_function_create ($2, script);
+ if (!grub_script_function_create ($2, script))
+ grub_script_free (script);
}
state->scripts = $<scripts>3;
diff --git a/include/grub/script_sh.h b/include/grub/script_sh.h
index b382bcf..6c48e07 100644
--- a/include/grub/script_sh.h
+++ b/include/grub/script_sh.h
@@ -361,6 +361,8 @@ struct grub_script_function
/* The next element. */
struct grub_script_function *next;
+
+ unsigned executing;
};
typedef struct grub_script_function *grub_script_function_t;
--
2.14.4
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