https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275099
Bug ID: 275099
Summary: cat(1) can't read directories
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: bin
Assignee: b...@freebsd.org
Reporter: msl0000023...@gmail.com
Attachment #246324 text/plain
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Created attachment 246324
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=246324&action=edit
helloworld-dir.c
While it is not common to read(2) a directory directly, this is still supported
in FreeBSD (with security.bsd.allow_read_dir=1); and it could be actually
useful in FUSE as an user space file system implementation may provide some
data in a directory itself.
The followings demonstrate the issue with a FUSE-based file system:
# sysctl security.bsd.allow_read_dir=1
security.bsd.allow_read_dir: 0 -> 1
# helloworld-dir /mnt/3/
# ls -al /mnt/3/
total 0
drwxr-xr-x 2 root wheel 27 Jan 1 1970 .
drwxr-xr-x 2 root wheel 13 Jan 1 1970 hello
# ls -al /mnt/3/hello/
total 0
drwxr-xr-x 2 root wheel 13 Jan 1 1970 .
drwxr-xr-x 2 root wheel 27 Jan 1 1970 ..
-rw-r--r-- 1 root wheel 12 Jan 1 1970 world
# cat /mnt/3/hello/world
Hello world
# cat /mnt/3/hello
cat: stdout: Is a directory
# dd status=none if=/mnt/3/hello
Hello world!
# cat /mnt/3/
cat: stdout: Is a directory
# dd status=none if=/mnt/3/
This is the root directory
# umount /mnt/3/
It shows that cat(1) failed to read the directories but dd(1) works without
problem.
The cause is that cat(1) tries to use copy_file_range(2) to copy input file to
stdout but this system call dosen't work on directories as documented, and
cat(1) didn't fallback to read(2) and write(2) on copy_file_range(2) fail with
EISDIR.
The FUSE program for demonstration is attached.
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