[PATCH] crypto: ccp - fix SFS ioctl race against device teardown

[Muhammad Bilal]

sfs_ioctl() reads psp_master->sfs_data and caches it in sfs_dev before
taking sfs_ioctl_mutex, while sfs_dev_destroy() frees sfs_dev->page
and sfs_dev->command_buf with no locking at all and only clears
psp->sfs_data afterwards. A call to sfs_ioctl() that reads sfs_data
just before sfs_dev_destroy() runs will still acquire the mutex and
go on to use the now-freed command buffer in send_sfs_cmd().

Have both functions take sfs_ioctl_mutex before touching
psp->sfs_data, so a call that is already using sfs_dev completes
before teardown can free it, and a call arriving after teardown sees
sfs_data cleared and returns -ENODEV instead of racing it.

Fixes: 648dbccc03a0 ("crypto: ccp - Add AMD Seamless Firmware Servicing (SFS) driver")
Signed-off-by: Muhammad Bilal <meatuni001@xxxxxxxxx>
---
 drivers/crypto/ccp/sfs.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/crypto/ccp/sfs.c b/drivers/crypto/ccp/sfs.c
index a4777839790b..530141f8bc74 100644
--- a/drivers/crypto/ccp/sfs.c
+++ b/drivers/crypto/ccp/sfs.c
@@ -111,13 +111,13 @@ static long sfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	struct sfs_device *sfs_dev;
 	int ret = 0;
 
+	guard(mutex)(&sfs_ioctl_mutex);
+
 	if (!psp_master || !psp_master->sfs_data)
 		return -ENODEV;
 
 	sfs_dev = psp_master->sfs_data;
 
-	guard(mutex)(&sfs_ioctl_mutex);
-
 	switch (cmd) {
 	case SFSIOCFWVERS:
 		dev_dbg(sfs_dev->dev, "in SFSIOCFWVERS\n");
@@ -191,8 +191,11 @@ static void sfs_exit(struct kref *ref)
 
 void sfs_dev_destroy(struct psp_device *psp)
 {
-	struct sfs_device *sfs_dev = psp->sfs_data;
+	struct sfs_device *sfs_dev;
+
+	guard(mutex)(&sfs_ioctl_mutex);
 
+	sfs_dev = psp->sfs_data;
 	if (!sfs_dev)
 		return;
 
-- 
2.55.0