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Subject[PATCH v2] fsi: occ: Prevent use after free
Date
Use get_device and put_device in the open and close functions to
make sure the device doesn't get freed while a file descriptor is
open.
Also, lock around the freeing of the device buffer and check the
buffer before using it in the submit function.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
---
Changes since v1:
- Add lock around freeing/nulling the buffer in occ_remove
- Don't bother checking the buffer in open or in write, only in submit

drivers/fsi/fsi-occ.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/fsi/fsi-occ.c b/drivers/fsi/fsi-occ.c
index c9cc75fbdfb9..28c176d038a2 100644
--- a/drivers/fsi/fsi-occ.c
+++ b/drivers/fsi/fsi-occ.c
@@ -94,6 +94,7 @@ static int occ_open(struct inode *inode, struct file *file)
client->occ = occ;
mutex_init(&client->lock);
file->private_data = client;
+ get_device(occ->dev);

/* We allocate a 1-page buffer, make sure it all fits */
BUILD_BUG_ON((OCC_CMD_DATA_BYTES + 3) > PAGE_SIZE);
@@ -197,6 +198,7 @@ static int occ_release(struct inode *inode, struct file *file)
{
struct occ_client *client = file->private_data;

+ put_device(client->occ->dev);
free_page((unsigned long)client->buffer);
kfree(client);

@@ -493,12 +495,19 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
for (i = 1; i < req_len - 2; ++i)
checksum += byte_request[i];

- mutex_lock(&occ->occ_lock);
+ rc = mutex_lock_interruptible(&occ->occ_lock);
+ if (rc)
+ return rc;

occ->client_buffer = response;
occ->client_buffer_size = user_resp_len;
occ->client_response_size = 0;

+ if (!occ->buffer) {
+ rc = -ENOENT;
+ goto done;
+ }
+
/*
* Get a sequence number and update the counter. Avoid a sequence
* number of 0 which would pass the response check below even if the
@@ -671,10 +680,13 @@ static int occ_remove(struct platform_device *pdev)
{
struct occ *occ = platform_get_drvdata(pdev);

- kvfree(occ->buffer);
-
misc_deregister(&occ->mdev);

+ mutex_lock(&occ->occ_lock);
+ kvfree(occ->buffer);
+ occ->buffer = NULL;
+ mutex_unlock(&occ->occ_lock);
+
device_for_each_child(&pdev->dev, NULL, occ_unregister_child);

ida_simple_remove(&occ_ida, occ->idx);
--
2.27.0
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