Fix double free and leak in the loader protocol #769
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If the EFI application exits, Shim will uninstall the protocols and then free the image. If something (e.g. GRUB) calls UnloadImage at this point, there is a double free because HandleProtocol() returns EFI_INVALID_PARAMETER and then Shim frees the image again. HandleProtocol() returns EFI_INVALID_PARAMETER because the handle is automatically freed when all protocols are uninstalled. Be robust against this and other errors by only freeing the image if HandleProtocol() returns EFI_SUCCESS. Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
This may happen if the image is loaded and then unloaded without calling StartImage(). Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
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Sorry about the noise with the checks; @bluca and I were working on it when your PR landed. |
bluca
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Aug 5, 2025
| else if (efi_status != EFI_SUCCESS) | ||
| return efi_status; | ||
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| flush_cached_sections(ImageHandle); |
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don't we need to flush the cached sections in either case here?
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I don't think so. If we hit the else if (efi_status != EFI_SUCCESS) case, either:
- We were passed a previously valid handle that was freed by the
UninstallMultipleProtocolInterfaces()call on line 389. In that case we have already called flush_cached_sections() on the handle (line 383) so nothing to do here. - We were passed NULL, garbage or an unknown handle, in which case we shouldn't call flush_cached_sections() on the handle.
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