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From 909e24465c59ba4df4124d7caa0730f609c33369 Mon Sep 17 00:00:00 2001
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From: Joe Lawrence <joe.lawrence@redhat.com>
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Date: Tue, 26 Oct 2021 18:00:19 -0400
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Subject: [KPATCH CVE-2020-36385] RDMA/ucma: kpatch fixes for CVE-2020-36385
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Changes since last build:
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arches: x86_64 ppc64le
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ucma.o: changed function: ucma_migrate_id
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---------------------------
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Kernels:
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4.18.0-305.el8
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4.18.0-305.3.1.el8_4
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4.18.0-305.7.1.el8_4
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4.18.0-305.10.2.el8_4
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4.18.0-305.12.1.el8_4
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4.18.0-305.17.1.el8_4
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4.18.0-305.19.1.el8_4
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Modifications:
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Kpatch-MR: https://gitlab.com/redhat/prdsc/rhel/src/kpatch/rhel-8/-/merge_requests/1
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Approved-by: Artem Savkov (@artem.savkov)
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- Avoid the complications of reworking all the locks (and preceding
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commits) and apply a minimal patch to avoid the CVE condition.
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- Always inline ucma_unlock_files() to avoid new function on x64_64
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Z-MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-8/-/merge_requests/961
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KT0 test PASS: https://beaker.engineering.redhat.com/jobs/5944203
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for kpatch-patch-4_18_0-305-1-6.el8 scratch build:
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https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=40633078
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commit 15152e7e191054883e2859892e77b442c531d1e1
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Author: Kamal Heib <kheib@redhat.com>
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Date: Sun Mar 7 11:30:04 2021 +0200
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RDMA/ucma: Rework ucma_migrate_id() to avoid races with destroy
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Bugzilla: https://bugzilla.redhat.com/1982040
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CVE: CVE-2020-36385
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Y-Commit: 20c1e291ce96ca474f5e94272d2e6511c6a38d58
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O-Bugzilla: http://bugzilla.redhat.com/1931846
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O-CVE: CVE-2020-36385
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commit f5449e74802c1112dea984aec8af7a33c4516af1
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Author: Jason Gunthorpe <jgg@nvidia.com>
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Date: Mon Sep 14 08:59:56 2020 -0300
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RDMA/ucma: Rework ucma_migrate_id() to avoid races with destroy
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ucma_destroy_id() assumes that all things accessing the ctx will do so via
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the xarray. This assumption violated only in the case the FD is being
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closed, then the ctx is reached via the ctx_list. Normally this is OK
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since ucma_destroy_id() cannot run concurrenty with release(), however
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with ucma_migrate_id() is involved this can violated as the close of the
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2nd FD can run concurrently with destroy on the first:
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CPU0 CPU1
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ucma_destroy_id(fda)
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ucma_migrate_id(fda -> fdb)
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ucma_get_ctx()
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xa_lock()
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_ucma_find_context()
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xa_erase()
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xa_unlock()
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xa_lock()
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ctx->file = new_file
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list_move()
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xa_unlock()
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ucma_put_ctx()
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ucma_close(fdb)
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_destroy_id()
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kfree(ctx)
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_destroy_id()
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wait_for_completion()
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// boom, ctx was freed
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The ctx->file must be modified under the handler and xa_lock, and prior to
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modification the ID must be rechecked that it is still reachable from
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cur_file, ie there is no parallel destroy or migrate.
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To make this work remove the double locking and streamline the control
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flow. The double locking was obsoleted by the handler lock now directly
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preventing new uevents from being created, and the ctx_list cannot be read
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while holding fgets on both files. Removing the double locking also
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removes the need to check for the same file.
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Fixes: 88314e4dda1e ("RDMA/cma: add support for rdma_migrate_id()")
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Link: https://lore.kernel.org/r/0-v1-05c5a4090305+3a872-ucma_syz_migrate_jgg@nvidia.com
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Reported-and-tested-by: syzbot+cc6fc752b3819e082d0c@syzkaller.appspotmail.com
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Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
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Signed-off-by: Kamal Heib <kheib@redhat.com>
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Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
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---
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drivers/infiniband/core/ucma.c | 11 ++++++++++-
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1 file changed, 10 insertions(+), 1 deletion(-)
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diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
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index 138e0096ca8e..2cd4277bf4a8 100644
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--- a/drivers/infiniband/core/ucma.c
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+++ b/drivers/infiniband/core/ucma.c
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@@ -1626,7 +1626,7 @@ static void ucma_lock_files(struct ucma_file *file1, struct ucma_file *file2)
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}
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}
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-static void ucma_unlock_files(struct ucma_file *file1, struct ucma_file *file2)
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+static __always_inline void ucma_unlock_files(struct ucma_file *file1, struct ucma_file *file2)
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{
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if (file1 < file2) {
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mutex_unlock(&file2->mut);
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@@ -1689,6 +1689,14 @@ static ssize_t ucma_migrate_id(struct ucma_file *new_file,
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ucma_lock_files(cur_file, new_file);
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xa_lock(&ctx_table);
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+ /* CVE-2020-36385 kpatch: double check the context one last time */
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+ if (_ucma_find_context(cmd.id, cur_file) != ctx) {
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+ xa_unlock(&ctx_table);
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+ ucma_unlock_files(cur_file, new_file);
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+ ret = -ENOENT;
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+ goto err_unlock;
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+ }
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+
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list_move_tail(&ctx->list, &new_file->ctx_list);
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ucma_move_events(ctx, new_file);
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ctx->file = new_file;
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@@ -1702,6 +1710,7 @@ static ssize_t ucma_migrate_id(struct ucma_file *new_file,
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&resp, sizeof(resp)))
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ret = -EFAULT;
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+err_unlock:
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ucma_put_ctx(ctx);
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file_put:
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fdput(f);
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--
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2.31.1
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