Bug 215849

Summary:	Cannot set POSIX ACL on tmpfs while in user namespace
Product:	File System	Reporter:	Peter Jin (peter)
Component:	Other	Assignee:	fs_other
Status:	NEW ---
Severity:	normal	CC:	brauner
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	5.17.3	Subsystem:
Regression:	No	Bisected commit-id:

Description Peter Jin 2022-04-17 20:07:39 UTC

Attempting to set a POSIX ACL on a tmpfs mount, where such tmpfs mount is made in a mount namespace owned by a non-initial user namespace, results in an "Invalid argument" error.


Steps to reproduce:

# unshare -U -m
(In another shell, write as root "0 1000 1\n100 10000 100\n" to both uid_map and gid_map of the resulting shell, where the 1000 in 0 1000 1 is the effective user/group ID of the original shell)
# mount -t tmpfs -o mode=0755 none /run
# mkdir -p -m 700 /run/test
# setfacl -m u:100:rx /run/test

Expected result: POSIX ACL set correctly on /run/test (mapped to UID 10000 in the init_user_ns)

Actual result: "setfacl: /run/test: Invalid argument"

Worked in Linux 5.16, broken in 5.17.

Comment 1 Christian Brauner 2022-04-19 07:50:31 UTC

Hey Peter,

Thanks for the report. I'll take a look now.

Comment 2 Christian Brauner 2022-04-19 11:51:07 UTC

Reproduced the issue and I have a fix for it.

Comment 3 Christian Brauner 2022-04-19 13:18:12 UTC

Cced you on the regression fix, Peter.