Arch Linux

coolreader18

Member

Registered: 2021-04-12

Posts: 4

exfat write() fails with EFAULT when the write size is zero

I have a drive mounted in /media with the options `rw,sync,noatime,noauto,user,exec`. Writing to any file in that filesystem with an empty buffer fails with "bad address":

>>> open("foo", "wb", buffering=0).write(b"")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 14] Bad address

Is anyone else experiencing this? Or can reproduce? I figure this is probably a kernel bug but I don't know what would even be causing it, based on a very cursory glance at the fs-exfat source code.

O239

Member

Registered: 2024-03-01

Posts: 7

Re: exfat write() fails with EFAULT when the write size is zero

I can reproduce this on my exfat-formatted flash drive.

notpeter

Member

Registered: 2024-12-12

Posts: 2

Re: exfat write() fails with EFAULT when the write size is zero

I am also able to reproduce this on Ubuntu Linux with an exFAT volume mounted from a file (no usb stick required).

mkdir /tmp/exfat
cd $_
fallocate -l 512M exfat.img
mkfs.exfat exfat.img
sudo mkdir -p /fatimagedir/
sudo mount -o umask=0022,gid=$(id -g),uid=$(id -u) /tmp/exfat/exfat.img /fatimagedir/
cd /fatimagedir
python3 -c 'open("foo", "wb", buffering=0).write(b"")'

Thanks for the simple repro steps @coolreader18.

I very much appreciate it.
See also: https://github.com/zed-industries/zed/issues/21595

xerxes_

Member

Registered: 2018-04-29

Posts: 1,055

Re: exfat write() fails with EFAULT when the write size is zero

What kernel version do you use?

notpeter

Member

Registered: 2024-12-12

Posts: 2

Re: exfat write() fails with EFAULT when the write size is zero

Stock Ubuntu 24.04

6.8.0-48-generic on x86_64

Last edited by notpeter (2024-12-13 18:43:26)

xerxes_

Member

Registered: 2018-04-29

Posts: 1,055

Re: exfat write() fails with EFAULT when the write size is zero

That kernel is old, from Ubuntu and probably unsupported on Arch. Try current kernel on current Arch Linux!

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 75,144

Re: exfat write() fails with EFAULT when the write size is zero

Tbf, this is also an older thread

Has anyone filed a bug at https://github.com/relan/exfat/issues ?
Doesn't seem to affect ntfs-3g, so probably not a fusermount thing.

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