Public bug reported:
When enabling shiftfs for LXD we get incorrect paths in /proc/*/maps
within a container:
root@anbox0:~# cat /proc/self/maps
55930e600000-55930e608000 r-xp 00000000 00:51 14509
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/bin/cat
55930e807000-55930e808000 r--p 00007000 00:51 14509
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/bin/cat
55930e808000-55930e809000 rw-p 00008000 00:51 14509
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/bin/cat
55930fd3c000-55930fd5d000 rw-p 00000000 00:00 0 [heap]
7fe736be2000-7fe736dc9000 r-xp 00000000 00:51 14226
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/libc-2.27.so
7fe736dc9000-7fe736fc9000 ---p 001e7000 00:51 14226
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/libc-2.27.so
7fe736fc9000-7fe736fcd000 r--p 001e7000 00:51 14226
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/libc-2.27.so
7fe736fcd000-7fe736fcf000 rw-p 001eb000 00:51 14226
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/libc-2.27.so
7fe736fcf000-7fe736fd3000 rw-p 00000000 00:00 0
7fe736fd3000-7fe736ffc000 r-xp 00000000 00:51 14139
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/ld-2.27.so
7fe7371ba000-7fe7371de000 rw-p 00000000 00:00 0
7fe7371fc000-7fe7371fd000 r--p 00029000 00:51 14139
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/ld-2.27.so
7fe7371fd000-7fe7371fe000 rw-p 0002a000 00:51 14139
/var/snap/lxd/common/lxd/storage-pools/default/containers/anbox0/rootfs/lib/x86_64-linux-gnu/ld-2.27.so
7fe7371fe000-7fe7371ff000 rw-p 00000000 00:00 0
7ffcd50a0000-7ffcd50c1000 rw-p 00000000 00:00 0 [stack]
7ffcd51d2000-7ffcd51d6000 r--p 00000000 00:00 0 [vvar]
7ffcd51d6000-7ffcd51d8000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0
[vsyscall]
When shiftfs is disabled the paths look all correct and are relative to
the root of the container
root@anbox0:~# cat /proc/self/maps
557aaa200000-557aaa208000 r-xp 00000000 00:48 14509
/bin/cat
557aaa407000-557aaa408000 r--p 00007000 00:48 14509
/bin/cat
557aaa408000-557aaa409000 rw-p 00008000 00:48 14509
/bin/cat
557aabaa5000-557aabac6000 rw-p 00000000 00:00 0 [heap]
7f4820526000-7f482070d000 r-xp 00000000 00:48 14226
/lib/x86_64-linux-gnu/libc-2.27.so
7f482070d000-7f482090d000 ---p 001e7000 00:48 14226
/lib/x86_64-linux-gnu/libc-2.27.so
7f482090d000-7f4820911000 r--p 001e7000 00:48 14226
/lib/x86_64-linux-gnu/libc-2.27.so
7f4820911000-7f4820913000 rw-p 001eb000 00:48 14226
/lib/x86_64-linux-gnu/libc-2.27.so
7f4820913000-7f4820917000 rw-p 00000000 00:00 0
7f4820917000-7f4820940000 r-xp 00000000 00:48 14139
/lib/x86_64-linux-gnu/ld-2.27.so
7f4820afe000-7f4820b22000 rw-p 00000000 00:00 0
7f4820b40000-7f4820b41000 r--p 00029000 00:48 14139
/lib/x86_64-linux-gnu/ld-2.27.so
7f4820b41000-7f4820b42000 rw-p 0002a000 00:48 14139
/lib/x86_64-linux-gnu/ld-2.27.so
7f4820b42000-7f4820b43000 rw-p 00000000 00:00 0
7ffd12ead000-7ffd12ece000 rw-p 00000000 00:00 0 [stack]
7ffd12fd8000-7ffd12fdc000 r--p 00000000 00:00 0 [vvar]
7ffd12fdc000-7ffd12fde000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0
[vsyscall]
To reproduce:
1. Use Ubuntu 20.04 or newer inluding shiftfs
2. Install LXD (4.0.x is good enough) and enable shiftfs support
$ snap install lxd
$ snap set lxd shiftfs.enable=true
$ snap restart lxd
$ lxd init --auto
3. Start a container and check /proc/self/maps
$ lxc launch ubuntu:f test0
$ lxc exec test0 -- cat /proc/self/maps
4. Turn shiftfs back off
$ snap set lxd shiftfs.enable=false
$ snap restart lxd
5. Check /proc/self/maps again inside the container
$ lxc exec test0 -- cat /proc/self/maps
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1968027
Title:
shiftfs breaks paths in /proc/*/maps
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