From 0b345d722e07d77866edffcf350449a4607026b6 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 3 Jan 2018 08:01:15 +1100 Subject: [PATCH] Documentation: security/credentials.rst: explain need to sort group_list This patch updates the documentation with the observations that led to commit bdcf0a423ea1 ("kernel: make groups_sort calling a responsibility group_info allocators") and the new behaviour required. Specifically that groups_sort() should be called on a new group_list before set_groups() or set_current_groups() is called. Signed-off-by: NeilBrown [jc: use proper :c:func: references] Signed-off-by: Jonathan Corbet --- Documentation/security/credentials.rst | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Documentation/security/credentials.rst b/Documentation/security/credentials.rst index 66a2e24939d8..5bb7125faeee 100644 --- a/Documentation/security/credentials.rst +++ b/Documentation/security/credentials.rst @@ -451,6 +451,13 @@ checks and hooks done. Both the current and the proposed sets of credentials are available for this purpose as current_cred() will return the current set still at this point. +When replacing the group list, the new list must be sorted before it +is added to the credential, as a binary search is used to test for +membership. In practice, this means :c:func:`groups_sort` should be +called before :c:func:`set_groups` or :c:func:`set_current_groups`. +:c:func:`groups_sort)` must not be called on a ``struct group_list`` which +is shared as it may permute elements as part of the sorting process +even if the array is already sorted. When the credential set is ready, it should be committed to the current process by calling::