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