Bug 14226

Summary:	Busybox md5sum fails to support backslashes in filenames
Product:	Busybox	Reporter:	Nils Rennebarth <nils.rennebarth>
Component:	Other	Assignee:	unassigned
Status:	NEW ---
Severity:	normal	CC:	busybox-cvs
Priority:	P5
Version:	1.33.x
Target Milestone:	---
Hardware:	All
OS:	Linux
Host:		Target:
Build:

Description Nils Rennebarth 2021-09-23 12:54:20 UTC

GNU coreutils md5sum since 2016 has a feature to make its output unambiguous even in the presence of linefeeds in filenames: It prints the filename with linefeeds escaped as \n. Of course that means is has to escape backslashes in filenames as
well. To mark a line as containing an escaped filename, it then adds a '\' at the start.

The busybox md5sum does not support this feature, and when run in check mode on a file generated by GNU coreutils md5sum, it will mark the corresponding file as 'FAILED'.

I checked the current sources and indeed, a line with an initial backslash is not handled differently. I only reviewed the code that implements -c, for full compatibility with GNU coreutils, generating md5sums will have to be adapted as well.

I might provide a patch if requested, currently I am working around this limitiation. Unfortunately, systemd decided to introduce filenames containing backslashes (sigh).

Comment 1 tlaurion 2023-01-11 17:02:45 UTC

The same behavior applies to sha256sum -c

For example (taken out of https://github.com/osresearch/heads/pull/1262#issuecomment-1377744973)

cd /boot
mkdir "$(echo -e 'hidden dir\b\b\b\b\b\b\b\b\b\bshowed dir')"
cd *hidden*
touch "$(echo -e 'file with newline\ncharacter')"
touch "file with textual new\nline"
find ./ -type f ! -path './kexec*' -print0 | xargs -0 sha256sum > /tmp/test
sha256sum -c /tmp/test | grep -v 'OK' 
sha256sum: can't open './showed dir/file with newline': No such file or directory
./showed dir/file with newline: FAILED
sha256sum: WARNING: 2 of 340 computed checksums did NOT match

cat /tmp/test
(exerpt)
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  ./showed dir/file with textual new\nline
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  ./showed dir/file with newline
character

cat /tmp/test | grep show
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  ./showed dir/file with textual new\nline
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  ./showed dir/file with newline

ls 
(exerpt)
hidden dir??????????showed dir

/boot # cd *hidden*
/boot/showed dir # ls
file with newline?character   file with textual new\nline

----
This impacts more than mda5/sha256: this extends to ls and other busybox applets