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mok: Avoid underflow in maximum variable size calculation #587

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Jul 19, 2023
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mok: Avoid underflow in maximum variable size calculation #587

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14 changes: 11 additions & 3 deletions mok.c
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Original file line number Diff line number Diff line change
Expand Up @@ -423,12 +423,20 @@ mirror_mok_db(CHAR16 *name, CHAR8 *name8, EFI_GUID *guid, UINT32 attrs,
}

/* The name counts towards the size of the variable */
max_var_sz -= (StrLen(namen) + 1) * 2;
SIZE_T namen_sz = (StrLen(namen) + 1) * 2;
if (max_var_sz > namen_sz)
max_var_sz -= namen_sz;
else
max_var_sz = 0;
dprint(L"max_var_sz - name: %lx\n", max_var_sz);

SIZE_T howmany;
howmany = MIN((max_var_sz - sizeof(*esl)) / esl->SignatureSize,
(esl_end_pos - pos) / esl->SignatureSize);
if (max_var_sz > sizeof(*esl))
howmany = MIN((max_var_sz - sizeof(*esl)) / esl->SignatureSize,
(esl_end_pos - pos) / esl->SignatureSize);
else
howmany = 0;

if (howmany == 0) {
/* No signatures from this ESL can be mirrored in to a
* single variable, so skip it.
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