From c17b58ebffbfa862b3f1815e208db340bd1664eb Mon Sep 17 00:00:00 2001
From: Yannick Cote <ycote@redhat.com>
Date: Tue, 1 Feb 2022 14:14:41 -0500
Subject: [KPATCH CVE-2020-0466] epoll: kpatch fixes for CVE-2020-0466

Kernels:
3.10.0-1160.15.2.el7
3.10.0-1160.21.1.el7
3.10.0-1160.24.1.el7
3.10.0-1160.25.1.el7
3.10.0-1160.31.1.el7
3.10.0-1160.36.2.el7
3.10.0-1160.41.1.el7
3.10.0-1160.42.2.el7
3.10.0-1160.45.1.el7
3.10.0-1160.49.1.el7
3.10.0-1160.53.1.el7

Changes since last build:
[x86_64]:
eventpoll.o: changed function: SyS_epoll_ctl
eventpoll.o: changed function: clear_tfile_check_list
eventpoll.o: changed function: ep_loop_check_proc

[ppc64le]:
eventpoll.o: changed function: SyS_epoll_ctl
eventpoll.o: changed function: ep_loop_check_proc

---------------------------

Kpatch-MR: https://gitlab.com/redhat/prdsc/rhel/src/kpatch/rhel-7/-/merge_requests/22
Approved-by: Artem Savkov (@artem.savkov)
Kernels:
3.10.0-1160.21.1.el7
3.10.0-1160.24.1.el7
3.10.0-1160.25.1.el7
3.10.0-1160.31.1.el7
3.10.0-1160.36.2.el7
3.10.0-1160.41.1.el7
3.10.0-1160.42.2.el7
3.10.0-1160.45.1.el7
3.10.0-1160.49.1.el7
3.10.0-1160.53.1.el7

Modifications: none

commit f771ed0537c55c506dc846cb8f3da60f6383a2b3
Author: Carlos Maiolino <cmaiolino@redhat.com>
Date:   Sat Dec 18 09:23:31 2021 +0100

    epoll: Keep a reference on files added to the check list

    Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2042760
    Tested: Sanity check only
    CVE: CVE-2020-0466

    Conflicts:
            - RHEL7 has no support for non-blocking do_epoll_ctl(), so the
              original patch got this part stripped.

    When adding a new fd to an epoll, and that this new fd is an
    epoll fd itself, we recursively scan the fds attached to it
    to detect cycles, and add non-epool files to a "check list"
    that gets subsequently parsed.

    However, this check list isn't completely safe when deletions
    can happen concurrently. To sidestep the issue, make sure that
    a struct file placed on the check list sees its f_count increased,
    ensuring that a concurrent deletion won't result in the file
    disapearing from under our feet.

    Cc: stable@vger.kernel.org
    Signed-off-by: Marc Zyngier <maz@kernel.org>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    (cherry picked from commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682)

    Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

commit 0875a380011a7ff7f4504b72890c29fec420d1cd
Author: Carlos Maiolino <cmaiolino@redhat.com>
Date:   Sat Dec 18 09:23:47 2021 +0100

    fix regression in "epoll: Keep a reference on files added to the check list"

    Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2042760
    Tested: Sanity check only
    CVE: CVE-2020-0466

    epoll_loop_check_proc() can run into a file already committed to destruction;
    we can't grab a reference on those and don't need to add them to the set for
    reverse path check anyway.

    Tested-by: Marc Zyngier <maz@kernel.org>
    Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    (cherry picked from commit 77f4689de17c0887775bb77896f4cc11a39bf848)

    Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

Signed-off-by: Yannick Cote <ycote@redhat.com>
---
 fs/eventpoll.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 6731b99a481f..ca0eb701eeb4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1750,9 +1750,11 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
 			 * not already there, and calling reverse_path_check()
 			 * during ep_insert().
 			 */
-			if (list_empty(&epi->ffd.file->f_tfile_llink))
-				list_add(&epi->ffd.file->f_tfile_llink,
-					 &tfile_check_list);
+			if (list_empty(&epi->ffd.file->f_tfile_llink)) {
+				if (get_file_rcu(epi->ffd.file))
+					list_add(&epi->ffd.file->f_tfile_llink,
+						 &tfile_check_list);
+			}
 		}
 	}
 	mutex_unlock(&ep->mtx);
@@ -1796,6 +1798,7 @@ static void clear_tfile_check_list(void)
 		file = list_first_entry(&tfile_check_list, struct file,
 					f_tfile_llink);
 		list_del_init(&file->f_tfile_llink);
+		fput(file);
 	}
 	INIT_LIST_HEAD(&tfile_check_list);
 }
@@ -1951,9 +1954,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 					clear_tfile_check_list();
 					goto error_tgt_fput;
 				}
-			} else
+			} else {
+				get_file(tf.file);
 				list_add(&tf.file->f_tfile_llink,
 							&tfile_check_list);
+			}
 			mutex_lock_nested(&ep->mtx, 0);
 			if (is_file_epoll(tf.file)) {
 				tep = tf.file->private_data;
-- 
2.26.3