From e2652ae6bd7492cdc0436817cbcd09282eb0bb03 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Tue, 21 Aug 2018 22:01:25 -0700 Subject: ipc: reorganize initialization of kern_ipc_perm.seq ipc_addid() initializes kern_ipc_perm.seq after having called idr_alloc() (within ipc_idr_alloc()). Thus a parallel semop() or msgrcv() that uses ipc_obtain_object_check() may see an uninitialized value. The patch moves the initialization of kern_ipc_perm.seq before the calls of idr_alloc(). Notes: 1) This patch has a user space visible side effect: If /proc/sys/kernel/*_next_id is used (i.e.: checkpoint/restore) and if semget()/msgget()/shmget() fails in the final step of adding the id to the rhash tree, then .._next_id is cleared. Before the patch, is remained unmodified. There is no change of the behavior after a successful ..get() call: It always clears .._next_id, there is no impact to non checkpoint/restore code as that code does not use .._next_id. 2) The patch correctly documents that after a call to ipc_idr_alloc(), the full tear-down sequence must be used. The callers of ipc_addid() do not fullfill that, i.e. more bugfixes are required. The patch is a squash of a patch from Dmitry and my own changes. Link: http://lkml.kernel.org/r/20180712185241.4017-3-manfred@colorfullife.com Reported-by: syzbot+2827ef6b3385deb07eaf@syzkaller.appspotmail.com Signed-off-by: Manfred Spraul Cc: Dmitry Vyukov Cc: Kees Cook Cc: Davidlohr Bueso Cc: Michael Kerrisk Cc: Davidlohr Bueso Cc: Herbert Xu Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/sysctl/kernel.txt | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'Documentation/sysctl/kernel.txt') diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index 9d38e75b19a0..37a679501ddc 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -464,7 +464,8 @@ Notes: 1) kernel doesn't guarantee, that new object will have desired id. So, it's up to userspace, how to handle an object with "wrong" id. 2) Toggle with non-default value will be set back to -1 by kernel after -successful IPC object allocation. +successful IPC object allocation. If an IPC object allocation syscall +fails, it is undefined if the value remains unmodified or is reset to -1. ============================================================== -- cgit v1.2.3