This bug was fixed in the package fuse-umfuse-ext2 -
0.4-1.1ubuntu0.17.04.1
---------------
fuse-umfuse-ext2 (0.4-1.1ubuntu0.17.04.1) zesty; urgency=high
* Correctly release locks in op_link (LP: #1674868).
-- Andrew Caldwell <andy.m.caldw...@googlemail.com> Wed, 22 Mar 2017
19:42:35 +0000
** Changed in: fuse-umfuse-ext2 (Ubuntu Zesty)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1674868
Title:
Fuse-ext2 deadlocks on creating symlinks
Status in fuse-umfuse-ext2 package in Ubuntu:
Fix Released
Status in fuse-umfuse-ext2 source package in Trusty:
Fix Released
Status in fuse-umfuse-ext2 source package in Xenial:
Fix Released
Status in fuse-umfuse-ext2 source package in Zesty:
Fix Released
Status in fuse-umfuse-ext2 source package in Artful:
Fix Released
Bug description:
[Impact]
* Any attempt to create/overwrite symlinks in a partition mounted by
fuseext2 causes the fuseext2 process to deadlock, preventing the
mounted filesystem from being used at all until the userspace process
is killed and the filesystem is remounted.
[Test Case]
* dd if=/dev/zero of=partition bs=1M count=200
* mkfs.ext2 partition
* mkdir mount
* fuseext2 partition mount -o rw+
* cd mount
* touch test
* ln -s test link - Doesn't complete
* In another shell try to do anything else in the mount directory (ls,
touch, rm) - Don't complete
[Regression Potential]
* Since this changes the locking strategy of the code to hold locks less,
the main risk is exposing a case where data can be accessed in a non-threadsafe
manner, leading to unexpected behaviour.
* The places where the change has been made are at the exit points of the
function, and match where similar unlocks are made in other places in the code.
* Since the program at risk is (by design) a userspace program, the risk of
kernel data leakage is minimal.
[Other Info]
* I can't actually work out where the upstream code for this project lives,
the only upstream I could find is https://github.com/alperakcan/fuse-ext2 but
that doesn't have any locking code at all (even in the reentrant branch) so I
can't see where this issue came from.
* This issue seems to apply to all versions of fuseext2 in the ubuntu repos
(well, at least it's there in trusty, xenial and zesty)
[Original Description]
Trying to create a symlink in a filesystem mounted by fuseext2 causes
the fuseext2 userspace process to deadlock before responding to the
fuse request. This is simply due to a code bug in fuse-ext2/op_link.c
(lines 104 and 109) where the code calls FUSE_EXT2_LOCK rather than
FUSE_EXT2_UNLOCK on exiting the function.
I've confirmed that making that changes allows me to create symlinks
happily on the mounted filesystem. The bug appears to exist upstream
too.
System info:
$ lsb_release -rd
Description: Linux Mint 18.1 Serena
Release: 18.1
Software version:
$ apt show fuseext2
Package: fuseext2
Version: 0.4-1.1
Priority: optional
Section: universe/misc
Source: fuse-umfuse-ext2
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-disc...@lists.ubuntu.com>
Original-Maintainer: Debian VSquare Team
<pkg-vsquare-de...@lists.alioth.debian.org>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 103 kB
Depends: e2fslibs (>= 1.42), libc6 (>= 2.4), libfuse2 (>= 2.8.1), fuse
Homepage: http://view-os.sourceforge.net
Download-Size: 24.7 kB
APT-Manual-Installed: yes
APT-Sources: http://archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
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