Package: fakeroot
Version: 1.20.2-1
Severity: normal
Tags: upstream
Dear Maintainer,
fakeroot does not work as expected inside user namespaces:
$ touch test-file
$ ls -ln test-file
-rw-r--r-- 1 1000 100 0 okt. 21 10:12 test-file
$ fakeroot -- chown 0:0 test-file ### WORKS
$ unshare -U -m fakeroot -- chown 0:0 test-file ### FAILS
chown: changing ownership of ‘test-file’: Invalid argument
I would have expected the last command to succeeded, like the one above it.
strace snippet, normal run (works):
fchownat(AT_FDCWD, "test-file", 0, 0, 0) = -1 EPERM (Operation not permitted)
Inside user namespace (fails):
fchownat(AT_FDCWD, "test-file", 0, 0, 0) = -1 EINVAL (Invalid argument)
A theory is that the linux kernel returns EINVAL when it encounters UIDs that
don't exist in the user namespace. There is of course the question whether that
is the _expected_ kernel behaviour, but I assume so. Anyway, the below command
backs up the theory about the kernel behaviour; it works because UID 0 exists
in this namespace:
$ unshare -U -m --map-root-user fakeroot -- chown 0:0 test-file ### WORKS
I did a small test with this patch:
@@ -870,7 +870,7 @@ int fchownat(int dir_fd, const char *path, uid_t owner,
gid_t group, int flags)
else
r=0;
- if(r&&(errno==EPERM))
+ if(r&&(errno==EPERM||errno==EINVAL))
r=0;
It fixed the problem for my little test case.
The question is what side-effects this patch may have, and whether it is a
sufficient and / or acceptable fix. There are probably many more syscalls that
may return EINVAL instead of EPERM in user namespaces.
-- System Information:
Debian Release: 8.2
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 3.16.0-4-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages fakeroot depends on:
ii libc6 2.19-18+deb8u1
ii libfakeroot 1.20.2-1
fakeroot recommends no packages.
fakeroot suggests no packages.
-- no debconf information
