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

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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
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3
grub-core/script/parser.y
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@ -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;