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From 7d389a33490309d15530e3372c3045110b3031ab Mon Sep 17 00:00:00 2001
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From: Artem Savkov <asavkov@redhat.com>
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Date: Tue, 4 Jan 2022 10:40:56 +0100
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Subject: [KPATCH CVE-2021-4154] cgroup: verify that source is a string
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Kernels:
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4.18.0-348.el8
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4.18.0-348.2.1.el8_5
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4.18.0-348.7.1.el8_5
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Changes since last build:
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arches: x86_64 ppc64le
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cgroup-v1.o: changed function: cgroup1_parse_param
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---------------------------
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Kpatch-MR: https://gitlab.com/redhat/prdsc/rhel/src/kpatch/rhel-8/-/merge_requests/9
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Approved-by: Yannick Cote (@ycote1)
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Approved-by: Joe Lawrence (@joe.lawrence)
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Kernels:
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4.18.0-348.el8
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4.18.0-348.2.1.el8_5
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4.18.0-348.7.1.el8_5
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4.18.0-348.12.2.el8_5
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Modifications: none
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Z-MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-8/-/merge_requests/1865
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CVE: CVE-2021-4154
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commit e1ee4bc6e6d8fd36b493fca941b7d5b6e987ae3c
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Author: Waiman Long <longman@redhat.com>
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Date: Tue Dec 21 09:47:25 2021 -0500
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cgroup: verify that source is a string
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Bugzilla: https://bugzilla.redhat.com/2034608
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Y-Commit: b6d2fff23b0eee0e82d128f23c4ebd99a30299c3
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O-Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2034609
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commit 3b0462726e7ef281c35a7a4ae33e93ee2bc9975b
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Author: Christian Brauner <christian.brauner@ubuntu.com>
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Date: Wed, 14 Jul 2021 15:47:49 +0200
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cgroup: verify that source is a string
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The following sequence can be used to trigger a UAF:
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int fscontext_fd = fsopen("cgroup");
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int fd_null = open("/dev/null, O_RDONLY);
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int fsconfig(fscontext_fd, FSCONFIG_SET_FD, "source", fd_null);
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close_range(3, ~0U, 0);
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The cgroup v1 specific fs parser expects a string for the "source"
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parameter. However, it is perfectly legitimate to e.g. specify a file
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descriptor for the "source" parameter. The fs parser doesn't know what
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a filesystem allows there. So it's a bug to assume that "source" is
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always of type fs_value_is_string when it can reasonably also be
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fs_value_is_file.
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This assumption in the cgroup code causes a UAF because struct
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fs_parameter uses a union for the actual value. Access to that union is
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guarded by the param->type member. Since the cgroup paramter parser
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didn't check param->type but unconditionally moved param->string into
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fc->source a close on the fscontext_fd would trigger a UAF during
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put_fs_context() which frees fc->source thereby freeing the file stashed
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in param->file causing a UAF during a close of the fd_null.
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Fix this by verifying that param->type is actually a string and report
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an error if not.
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In follow up patches I'll add a new generic helper that can be used here
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and by other filesystems instead of this error-prone copy-pasta fix.
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But fixing it in here first makes backporting a it to stable a lot
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easier.
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Fixes: 8d2451f4994f ("cgroup1: switch to option-by-option parsing")
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Reported-by: syzbot+283ce5a46486d6acdbaf@syzkaller.appspotmail.com
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Cc: Christoph Hellwig <hch@lst.de>
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Cc: Alexander Viro <viro@zeniv.linux.org.uk>
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Cc: Dmitry Vyukov <dvyukov@google.com>
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Cc: <stable@kernel.org>
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Cc: syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Waiman Long <longman@redhat.com>
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Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>
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Signed-off-by: Artem Savkov <asavkov@redhat.com>
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---
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kernel/cgroup/cgroup-v1.c | 2 ++
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1 file changed, 2 insertions(+)
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diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
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index 852f1349f9d9..291754068ec6 100644
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--- a/kernel/cgroup/cgroup-v1.c
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+++ b/kernel/cgroup/cgroup-v1.c
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@@ -907,6 +907,8 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
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opt = fs_parse(fc, cgroup1_fs_parameters, param, &result);
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if (opt == -ENOPARAM) {
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if (strcmp(param->key, "source") == 0) {
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+ if (param->type != fs_value_is_string)
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+ return invalf(fc, "Non-string source");
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if (fc->source)
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return invalf(fc, "Multiple sources not supported");
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fc->source = param->string;
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--
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2.34.1
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