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commit 03333cabcf9a39624f7fe4e6ffe9b854e95008a7
Author: Milos Nikic <[email protected]>
Date: Mon Oct 5 15:34:26 2026 -0700
ext2fs: Do not crash when poking a page that cannot be written
Before a truncate, force_delayed_copies maps the file and writes every
page past the new size, so that delayed copies of the data are made
before it is discarded. When the write fault on such a page fails, for
instance because an earlier pager_unlock_page for it found no free
block, libpager answers the fault with memory_object_data_error and the
kernel raises a memory exception in ext2fs itself. diskfs_catch_exception
only covers faults on the disk image, so the exception kills the
translator. Filling the filesystem and truncating a file whose writes
failed is enough to crash it, with or without a journal.
Poke each page with hurd_safe_copyin and hurd_safe_copyout, which catch
the fault, and skip a page that faults. The page lies past the new size
and is discarded anyway. A delayed copy of such a page is then not
forced, so a holder of that copy can see it as zeros; the page could not
be written in the first place.
To reproduce:
- fill an ext2 filesystem until writes fail with ENOSPC,
then truncate one of the files whose writes failed;
the ext2fs translator dies with SIGBUS in poke_pages,
with or without a journal.
With this fix fsck remains clean in such a case with or
without a journal.
Message-ID: <[email protected]>
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Summary of changes:
ext2fs/truncate.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
hooks/post-receive
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