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From c17b58ebffbfa862b3f1815e208db340bd1664eb Mon Sep 17 00:00:00 2001
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From: Yannick Cote <ycote@redhat.com>
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Date: Tue, 1 Feb 2022 14:14:41 -0500
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Subject: [KPATCH CVE-2020-0466] epoll: kpatch fixes for CVE-2020-0466
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Kernels:
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3.10.0-1160.15.2.el7
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3.10.0-1160.21.1.el7
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3.10.0-1160.24.1.el7
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3.10.0-1160.25.1.el7
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3.10.0-1160.31.1.el7
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3.10.0-1160.36.2.el7
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3.10.0-1160.41.1.el7
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3.10.0-1160.42.2.el7
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3.10.0-1160.45.1.el7
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3.10.0-1160.49.1.el7
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3.10.0-1160.53.1.el7
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Changes since last build:
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[x86_64]:
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eventpoll.o: changed function: SyS_epoll_ctl
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eventpoll.o: changed function: clear_tfile_check_list
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eventpoll.o: changed function: ep_loop_check_proc
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[ppc64le]:
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eventpoll.o: changed function: SyS_epoll_ctl
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eventpoll.o: changed function: ep_loop_check_proc
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---------------------------
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Kpatch-MR: https://gitlab.com/redhat/prdsc/rhel/src/kpatch/rhel-7/-/merge_requests/22
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Approved-by: Artem Savkov (@artem.savkov)
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Kernels:
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3.10.0-1160.21.1.el7
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3.10.0-1160.24.1.el7
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3.10.0-1160.25.1.el7
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3.10.0-1160.31.1.el7
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3.10.0-1160.36.2.el7
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3.10.0-1160.41.1.el7
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3.10.0-1160.42.2.el7
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3.10.0-1160.45.1.el7
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3.10.0-1160.49.1.el7
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3.10.0-1160.53.1.el7
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Modifications: none
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commit f771ed0537c55c506dc846cb8f3da60f6383a2b3
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Author: Carlos Maiolino <cmaiolino@redhat.com>
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Date: Sat Dec 18 09:23:31 2021 +0100
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epoll: Keep a reference on files added to the check list
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2042760
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Tested: Sanity check only
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CVE: CVE-2020-0466
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Conflicts:
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- RHEL7 has no support for non-blocking do_epoll_ctl(), so the
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original patch got this part stripped.
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When adding a new fd to an epoll, and that this new fd is an
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epoll fd itself, we recursively scan the fds attached to it
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to detect cycles, and add non-epool files to a "check list"
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that gets subsequently parsed.
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However, this check list isn't completely safe when deletions
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can happen concurrently. To sidestep the issue, make sure that
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a struct file placed on the check list sees its f_count increased,
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ensuring that a concurrent deletion won't result in the file
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disapearing from under our feet.
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Cc: stable@vger.kernel.org
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Signed-off-by: Marc Zyngier <maz@kernel.org>
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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(cherry picked from commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682)
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Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
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commit 0875a380011a7ff7f4504b72890c29fec420d1cd
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Author: Carlos Maiolino <cmaiolino@redhat.com>
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Date: Sat Dec 18 09:23:47 2021 +0100
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fix regression in "epoll: Keep a reference on files added to the check list"
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2042760
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Tested: Sanity check only
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CVE: CVE-2020-0466
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epoll_loop_check_proc() can run into a file already committed to destruction;
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we can't grab a reference on those and don't need to add them to the set for
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reverse path check anyway.
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Tested-by: Marc Zyngier <maz@kernel.org>
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Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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(cherry picked from commit 77f4689de17c0887775bb77896f4cc11a39bf848)
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Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
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Signed-off-by: Yannick Cote <ycote@redhat.com>
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---
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fs/eventpoll.c | 13 +++++++++----
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1 file changed, 9 insertions(+), 4 deletions(-)
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diff --git a/fs/eventpoll.c b/fs/eventpoll.c
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index 6731b99a481f..ca0eb701eeb4 100644
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--- a/fs/eventpoll.c
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+++ b/fs/eventpoll.c
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@@ -1750,9 +1750,11 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
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* not already there, and calling reverse_path_check()
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* during ep_insert().
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*/
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- if (list_empty(&epi->ffd.file->f_tfile_llink))
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- list_add(&epi->ffd.file->f_tfile_llink,
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- &tfile_check_list);
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+ if (list_empty(&epi->ffd.file->f_tfile_llink)) {
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+ if (get_file_rcu(epi->ffd.file))
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+ list_add(&epi->ffd.file->f_tfile_llink,
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+ &tfile_check_list);
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+ }
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}
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}
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mutex_unlock(&ep->mtx);
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@@ -1796,6 +1798,7 @@ static void clear_tfile_check_list(void)
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file = list_first_entry(&tfile_check_list, struct file,
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f_tfile_llink);
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list_del_init(&file->f_tfile_llink);
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+ fput(file);
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}
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INIT_LIST_HEAD(&tfile_check_list);
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}
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@@ -1951,9 +1954,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
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clear_tfile_check_list();
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goto error_tgt_fput;
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}
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- } else
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+ } else {
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+ get_file(tf.file);
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list_add(&tf.file->f_tfile_llink,
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&tfile_check_list);
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+ }
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mutex_lock_nested(&ep->mtx, 0);
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if (is_file_epoll(tf.file)) {
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tep = tf.file->private_data;
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--
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2.26.3
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