tree b721c9f59b665421dc5ef8ebcee9d38edf8cf12b
parent dfeb4f0d79351dc0256b45c7a9f26c752c4e0e09
author Sam Edwards <cfsworks@gmail.com> 1699715944 -0700
committer Tom Rini <trini@konsulko.com> 1700179198 -0500

fs: btrfs: fix reading when length specified

The btrfs read function limits the read length to ensure that it
and the read offset do not together exceed the size of the file.
However, this size was only being queried if the read length was
passed a value of zero (meaning "whole file"), and the size is
defaulted to 0 otherwise. This means the clamp will just zero out
the length if one is specified, preventing reading of the file.

Fix this by checking the file size unconditionally, and unifying
the default length and clamping logic as a single range check instead.

This bug was discovered when trying to boot Linux with initrd= via
'bootefi' from a btrfs partition. The EFI stub entered an infinite
loop of zero-length reads while trying to read the initrd, and the
boot process stalled indefinitely.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>