Fix the fallback mechanism when menu entries fail to boot #195
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grub_script_execute_sourcecode() parses and executes code one line at a time, updating the return code each time because only the last line determines the final status. However, trailing new lines were also executed, masking any failure on the previous line. Fix this by only trying to execute the command when there is actually one present. This has presumably never been noticed because this code is not used by regular functions, only in special cases like eval and menu entries. The latter generally don't return at all, having booted an OS. When failing to boot, upstream GRUB triggers the fallback mechanism regardless of the return code. We noticed the problem while using Red Hat's patches, which change this behaviour to take account of the return code. In that case, a failure takes you back to the menu rather than triggering a fallback. Signed-off-by: James Le Cuirot <[email protected]>
Don't rely on grub_errno here because grub_script_execute_new_scope() calls grub_print_error(), which always resets grub_errno back to GRUB_ERR_NONE. It may also get reset by grub_wait_after_message(). This problem was observed when a "bad signature" error resulted in the menu being redisplayed rather than the fallback mechanism being triggered, although another change was also needed to fix it. This only happens with Red Hat's patches because upstream GRUB triggers the fallback mechanism regardless of the return code. Signed-off-by: James Le Cuirot <[email protected]>
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@martinezjavier's c3fcfe5 commit accidentally broke the fallback mechanism, although it also exposed another bug in upstream GRUB.
We cannot rely on
grub_errnoingrub_menu_execute_entry()becausegrub_script_execute_new_scope()callsgrub_print_error(), which always resetsgrub_errnoback toGRUB_ERR_NONE. It may also get reset bygrub_wait_after_message().grub_script_execute_sourcecode()parses and executes code one line at a time, updating the return code each time because only the last line determines the final status. However, trailing new lines were also executed, masking any failure on the previous line. Fix this by only trying to execute the command when there is actually one present. A new test case is included.See the commit messages for further details.
I can send the first change upstream, although it's unlikely to cause issues without your change, hence why it went unnoticed for so long. I gather you are starting to upstream some of your changes, so perhaps I can leave it with you?