The patch below does not apply to the 5.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f5449e74802c1112dea984aec8af7a33c4516af1 Mon Sep 17 00:00:00 2001
From: Jason Gunthorpe jgg@ziepe.ca Date: Mon, 14 Sep 2020 08:59:56 -0300 Subject: [PATCH] RDMA/ucma: Rework ucma_migrate_id() to avoid races with destroy
ucma_destroy_id() assumes that all things accessing the ctx will do so via the xarray. This assumption violated only in the case the FD is being closed, then the ctx is reached via the ctx_list. Normally this is OK since ucma_destroy_id() cannot run concurrenty with release(), however with ucma_migrate_id() is involved this can violated as the close of the 2nd FD can run concurrently with destroy on the first:
CPU0 CPU1 ucma_destroy_id(fda) ucma_migrate_id(fda -> fdb) ucma_get_ctx() xa_lock() _ucma_find_context() xa_erase() xa_unlock() xa_lock() ctx->file = new_file list_move() xa_unlock() ucma_put_ctx()
ucma_close(fdb) _destroy_id() kfree(ctx)
_destroy_id() wait_for_completion() // boom, ctx was freed
The ctx->file must be modified under the handler and xa_lock, and prior to modification the ID must be rechecked that it is still reachable from cur_file, ie there is no parallel destroy or migrate.
To make this work remove the double locking and streamline the control flow. The double locking was obsoleted by the handler lock now directly preventing new uevents from being created, and the ctx_list cannot be read while holding fgets on both files. Removing the double locking also removes the need to check for the same file.
Fixes: 88314e4dda1e ("RDMA/cma: add support for rdma_migrate_id()") Link: https://lore.kernel.org/r/0-v1-05c5a4090305+3a872-ucma_syz_migrate_jgg@nvidi... Reported-and-tested-by: syzbot+cc6fc752b3819e082d0c@syzkaller.appspotmail.com Signed-off-by: Jason Gunthorpe jgg@nvidia.com
diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c index a5595bd489b0..b3a7dbb12f25 100644 --- a/drivers/infiniband/core/ucma.c +++ b/drivers/infiniband/core/ucma.c @@ -1587,45 +1587,15 @@ static ssize_t ucma_leave_multicast(struct ucma_file *file, return ret; }
-static void ucma_lock_files(struct ucma_file *file1, struct ucma_file *file2) -{ - /* Acquire mutex's based on pointer comparison to prevent deadlock. */ - if (file1 < file2) { - mutex_lock(&file1->mut); - mutex_lock_nested(&file2->mut, SINGLE_DEPTH_NESTING); - } else { - mutex_lock(&file2->mut); - mutex_lock_nested(&file1->mut, SINGLE_DEPTH_NESTING); - } -} - -static void ucma_unlock_files(struct ucma_file *file1, struct ucma_file *file2) -{ - if (file1 < file2) { - mutex_unlock(&file2->mut); - mutex_unlock(&file1->mut); - } else { - mutex_unlock(&file1->mut); - mutex_unlock(&file2->mut); - } -} - -static void ucma_move_events(struct ucma_context *ctx, struct ucma_file *file) -{ - struct ucma_event *uevent, *tmp; - - list_for_each_entry_safe(uevent, tmp, &ctx->file->event_list, list) - if (uevent->ctx == ctx) - list_move_tail(&uevent->list, &file->event_list); -} - static ssize_t ucma_migrate_id(struct ucma_file *new_file, const char __user *inbuf, int in_len, int out_len) { struct rdma_ucm_migrate_id cmd; struct rdma_ucm_migrate_resp resp; + struct ucma_event *uevent, *tmp; struct ucma_context *ctx; + LIST_HEAD(event_list); struct fd f; struct ucma_file *cur_file; int ret = 0; @@ -1641,43 +1611,52 @@ static ssize_t ucma_migrate_id(struct ucma_file *new_file, ret = -EINVAL; goto file_put; } + cur_file = f.file->private_data;
/* Validate current fd and prevent destruction of id. */ - ctx = ucma_get_ctx(f.file->private_data, cmd.id); + ctx = ucma_get_ctx(cur_file, cmd.id); if (IS_ERR(ctx)) { ret = PTR_ERR(ctx); goto file_put; }
rdma_lock_handler(ctx->cm_id); - cur_file = ctx->file; - if (cur_file == new_file) { - mutex_lock(&cur_file->mut); - resp.events_reported = ctx->events_reported; - mutex_unlock(&cur_file->mut); - goto response; - } - /* - * Migrate events between fd's, maintaining order, and avoiding new - * events being added before existing events. + * ctx->file can only be changed under the handler & xa_lock. xa_load() + * must be checked again to ensure the ctx hasn't begun destruction + * since the ucma_get_ctx(). */ - ucma_lock_files(cur_file, new_file); xa_lock(&ctx_table); - - list_move_tail(&ctx->list, &new_file->ctx_list); - ucma_move_events(ctx, new_file); + if (_ucma_find_context(cmd.id, cur_file) != ctx) { + xa_unlock(&ctx_table); + ret = -ENOENT; + goto err_unlock; + } ctx->file = new_file; + xa_unlock(&ctx_table); + + mutex_lock(&cur_file->mut); + list_del(&ctx->list); + /* + * At this point lock_handler() prevents addition of new uevents for + * this ctx. + */ + list_for_each_entry_safe(uevent, tmp, &cur_file->event_list, list) + if (uevent->ctx == ctx) + list_move_tail(&uevent->list, &event_list); resp.events_reported = ctx->events_reported; + mutex_unlock(&cur_file->mut);
- xa_unlock(&ctx_table); - ucma_unlock_files(cur_file, new_file); + mutex_lock(&new_file->mut); + list_add_tail(&ctx->list, &new_file->ctx_list); + list_splice_tail(&event_list, &new_file->event_list); + mutex_unlock(&new_file->mut);
-response: if (copy_to_user(u64_to_user_ptr(cmd.response), &resp, sizeof(resp))) ret = -EFAULT;
+err_unlock: rdma_unlock_handler(ctx->cm_id); ucma_put_ctx(ctx); file_put: