vbatts/grub
1
0
Fork 0
Code Issues Pull requests Releases Wiki Activity

script: Avoid a use-after-free when redefining a function during execution

Browse source 
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>
This commit is contained in:
Chris Coulson 2020-07-10 14:41:45 +01:00 • committed by Daniel Kiper
parent 1a8d9c9b4a
commit 426f57383d
4 changed files with 19 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

16
grub-core/script/function.c
View file

@ -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
{