Merge: list: fix a data-race around ep->rdllist

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6522

JIRA: https://issues.redhat.com/browse/RHEL-80985
CVE: CVE-2022-49443
Upstream Status: linux.git

commit d679ae9
Author: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Date:   Fri Apr 29 14:38:01 2022 -0700

    ep_poll() first calls ep_events_available() with no lock held and checks
    if ep->rdllist is empty by list_empty_careful(), which reads
    rdllist->prev.  Thus all accesses to it need some protection to avoid
    store/load-tearing.

    Note INIT_LIST_HEAD_RCU() already has the annotation for both prev
    and next.

    Commit bf3b9f6 ("epoll: Add busy poll support to epoll with socket
    fds.") added the first lockless ep_events_available(), and commit
    c5a282e ("fs/epoll: reduce the scope of wq lock in epoll_wait()")
    made some ep_events_available() calls lockless and added single call under
    a lock, finally commit e59d3c6 ("epoll: eliminate unnecessary lock
    for zero timeout") made the last ep_events_available() lockless.

    BUG: KCSAN: data-race in do_epoll_wait / do_epoll_wait

    write to 0xffff88810480c7d8 of 8 bytes by task 1802 on cpu 0:
     INIT_LIST_HEAD include/linux/list.h:38 [inline]
     list_splice_init include/linux/list.h:492 [inline]
     ep_start_scan fs/eventpoll.c:622 [inline]
     ep_send_events fs/eventpoll.c:1656 [inline]
     ep_poll fs/eventpoll.c:1806 [inline]
     do_epoll_wait+0x4eb/0xf40 fs/eventpoll.c:2234
     do_epoll_pwait fs/eventpoll.c:2268 [inline]
     __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline]
     __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275
     __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275
     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
     do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
     entry_SYSCALL_64_after_hwframe+0x44/0xae

    read to 0xffff88810480c7d8 of 8 bytes by task 1799 on cpu 1:
     list_empty_careful include/linux/list.h:329 [inline]
     ep_events_available fs/eventpoll.c:381 [inline]
     ep_poll fs/eventpoll.c:1797 [inline]
     do_epoll_wait+0x279/0xf40 fs/eventpoll.c:2234
     do_epoll_pwait fs/eventpoll.c:2268 [inline]
     __do_sys_epoll_pwait fs/eventpoll.c:2281 [inline]
     __se_sys_epoll_pwait+0x12b/0x240 fs/eventpoll.c:2275
     __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2275
     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
     do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
     entry_SYSCALL_64_after_hwframe+0x44/0xae

    value changed: 0xffff88810480c7d0 -> 0xffff888103c15098

    Reported by Kernel Concurrency Sanitizer on:
    CPU: 1 PID: 1799 Comm: syz-fuzzer Tainted: G        W         5.17.0-rc7-syzkaller-dirty #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

    Link: https://lkml.kernel.org/r/20220322002653.33865-3-kuniyu@amazon.co.jp
    Fixes: e59d3c6 ("epoll: eliminate unnecessary lock for zero timeout")
    Fixes: c5a282e ("fs/epoll: reduce the scope of wq lock in epoll_wait()")
    Fixes: bf3b9f6 ("epoll: Add busy poll support to epoll with socket fds.")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
    Reported-by: syzbot+bdd6e38a1ed5ee58d8bd@syzkaller.appspotmail.com
    Cc: Al Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>
    Cc: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
    Cc: Kuniyuki Iwashima <kuni1840@gmail.com>
    Cc: "Soheil Hassas Yeganeh" <soheil@google.com>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: "Sridhar Samudrala" <sridhar.samudrala@intel.com>
    Cc: Alexander Duyck <alexander.h.duyck@intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Jan Stancek <jstancek@redhat.com>

Approved-by: Waiman Long <longman@redhat.com>
Approved-by: Herton R. Krzesinski <herton@redhat.com>
Approved-by: Rafael Aquini <raquini@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Augusto Caringi <acaringi@redhat.com>

Author: caringi

include/linux/list.h

@@ -33,7 +33,7 @@
 static inline void INIT_LIST_HEAD(struct list_head *list)
 {
 	WRITE_ONCE(list->next, list);
-	list->prev = list;
+	WRITE_ONCE(list->prev, list);
 }
 
 #ifdef CONFIG_DEBUG_LIST
@@ -304,7 +304,7 @@ static inline int list_empty(const struct list_head *head)
 static inline void list_del_init_careful(struct list_head *entry)
 {
 	__list_del_entry(entry);
-	entry->prev = entry;
+	WRITE_ONCE(entry->prev, entry);
 	smp_store_release(&entry->next, entry);
 }
 
@@ -324,7 +324,7 @@ static inline void list_del_init_careful(struct list_head *entry)
 static inline int list_empty_careful(const struct list_head *head)
 {
 	struct list_head *next = smp_load_acquire(&head->next);
-	return list_is_head(next, head) && (next == head->prev);
+	return list_is_head(next, head) && (next == READ_ONCE(head->prev));
 }
 
 /**