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boot: do not truncate random seed file

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There are concerns about the FAT file system driver exploding if we try
to do this, so just leave the bytes zeroed out instead.
This commit is contained in:
Jason A. Donenfeld
2022-11-17 12:22:32 +01:00
parent 3daeef0884
commit 5d29d07b34
1 changed files with 12 additions and 5 deletions
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src/boot/efi/random-seed.c
+12 -5
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@@ -263,7 +263,7 @@ EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
sha256_finish_ctx(&hash, random_bytes);
size = sizeof(random_bytes);
/* If the file size is too large, zero out the remaining bytes on disk, and then truncate. */
/* If the file size is too large, zero out the remaining bytes on disk. */
if (size < info->FileSize) {
err = handle->SetPosition(handle, size);
if (err != EFI_SUCCESS)
@@ -280,10 +280,17 @@ EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
err = handle->SetPosition(handle, 0);
if (err != EFI_SUCCESS)
return log_error_status_stall(err, L"Failed to seek to beginning of random seed file: %r", err);
info->FileSize = size;
err = handle->SetInfo(handle, &GenericFileInfo, info->Size, info);
if (err != EFI_SUCCESS)
return log_error_status_stall(err, L"Failed to truncate random seed file: %r", err);
/* We could truncate the file here with something like:
*
* info->FileSize = size;
* err = handle->SetInfo(handle, &GenericFileInfo, info->Size, info);
* if (err != EFI_SUCCESS)
* return log_error_status_stall(err, L"Failed to truncate random seed file: %r", err);
*
* But this is considered slightly risky, because EFI filesystem drivers are a little bit
* flimsy. So instead we rely on userspace eventually truncating this when it writes a new
* seed. For now the best we do is zero it. */
}
/* Update the random seed on disk before we use it */
wsize = size;