userns: relax the posix_acl_valid() checks

So far, POSIX ACLs are using a canonical representation that keeps all ACL
entries in a strict order; the ACL_USER and ACL_GROUP entries for specific
users and groups are ordered by user and group identifier, respectively.
The user-space code provides ACL entries in this order; the kernel
verifies that the ACL entry order is correct in posix_acl_valid().

User namespaces allow to arbitrary map user and group identifiers which
can cause the ACL_USER and ACL_GROUP entry order to differ between user
space and the kernel; posix_acl_valid() would then fail.

Work around this by allowing ACL_USER and ACL_GROUP entries to be in any
order in the kernel.  The effect is only minor: file permission checks
will pick the first matching ACL_USER entry, and check all matching
ACL_GROUP entries.

(The libacl user-space library and getfacl / setfacl tools will not create
ACLs with duplicate user or group idenfifiers; they will handle ACLs with
entries in an arbitrary order correctly.)

Signed-off-by: Andreas Gruenbacher <>
Cc: Eric W. Biederman <>
Cc: Theodore Tso <>
Cc: Christoph Hellwig <>
Cc: Andreas Dilger <>
Cc: Jan Kara <>
Cc: Al Viro <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
1 file changed