[PATCH] cxl/mem: Fixes to IOCTL interface

From: Ben Widawsky <ben.widawsky@intel.com>
To: Dan Williams <dan.j.williams@intel.com>,
	linux-cxl@vger.kernel.org, linux-nvdimm@lists.01.org
Cc: Alison Schofield <alison.schofield@intel.com>,
	Ben Widawsky <ben.widawsky@intel.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>
Subject: [PATCH] cxl/mem: Fixes to IOCTL interface
Date: Sat, 20 Feb 2021 13:56:41 -0800	[thread overview]
Message-ID: <20210220215641.604535-1-ben.widawsky@intel.com> (raw)

When submitting a command for userspace, input and output payload bounce
buffers are allocated. For a given command, both input and output
buffers may exist and so when allocation of the input buffer fails, the
output buffer must be freed. As far as I can tell, userspace can't
easily exploit the leak to OOM a machine unless the machine was already
near OOM state.

This bug was introduced in v5 of the patch and did not exist in prior
revisions.

While here, adjust the variable 'j' found in patch review by Konrad.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com> (v2)
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/cxl/mem.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index df895bcca63a..626fd7066f4f 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -514,8 +514,10 @@ static int handle_mailbox_cmd_from_user(struct cxl_mem *cxlm,
 	if (cmd->info.size_in) {
 		mbox_cmd.payload_in = vmemdup_user(u64_to_user_ptr(in_payload),
 						   cmd->info.size_in);
-		if (IS_ERR(mbox_cmd.payload_in))
+		if (IS_ERR(mbox_cmd.payload_in)) {
+			kvfree(mbox_cmd.payload_out);
 			return PTR_ERR(mbox_cmd.payload_in);
+		}
 	}
 
 	rc = cxl_mem_mbox_get(cxlm);
@@ -696,7 +698,7 @@ static int cxl_query_cmd(struct cxl_memdev *cxlmd,
 	struct device *dev = &cxlmd->dev;
 	struct cxl_mem_command *cmd;
 	u32 n_commands;
-	int j = 0;
+	int cmds = 0;
 
 	dev_dbg(dev, "Query IOCTL\n");
 
@@ -714,10 +716,10 @@ static int cxl_query_cmd(struct cxl_memdev *cxlmd,
 	cxl_for_each_cmd(cmd) {
 		const struct cxl_command_info *info = &cmd->info;
 
-		if (copy_to_user(&q->commands[j++], info, sizeof(*info)))
+		if (copy_to_user(&q->commands[cmds++], info, sizeof(*info)))
 			return -EFAULT;
 
-		if (j == n_commands)
+		if (cmds == n_commands)
 			break;
 	}
 
-- 
2.30.1
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