commit 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race") introduced an incorrect WARN_ON_ONCE() and missed a sequence where sg_device_destroy() was used after scsi_device_put().

sg_device_destroy() is accessing the parent scsi_device request_queue which will already be set to NULL when the preceding call to scsi_device_put() removed the last reference to the parent scsi_device.

Drop the incorrect WARN_ON_ONCE() - allowing more than one concurrent access to the sg device - and make sure sg_device_destroy() is not used after scsi_device_put() in the error handling.

Link: https://lore.kernel.org/all/5375B275-D137-4D5F-BE25-6AF8ACAE41EF@linux.ibm.c... Fixes: 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race") Cc: stable@vger.kernel.org Signed-off-by: Alexander Wetzel Alexander@wetzel-home.de ---

Changes compared to V1: fixed commit message Changes compared to V2: Fix use-after free --- drivers/scsi/sg.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 386981c6976a..baf870a03ecf 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -285,6 +285,7 @@ sg_open(struct inode *inode, struct file *filp) int dev = iminor(inode); int flags = filp->f_flags; struct request_queue *q; + struct scsi_device *device; Sg_device *sdp; Sg_fd *sfp; int retval; @@ -301,11 +302,12 @@ sg_open(struct inode *inode, struct file *filp)

/* This driver's module count bumped by fops_get in <linux/fs.h> */ /* Prevent the device driver from vanishing while we sleep */ - retval = scsi_device_get(sdp->device); + device = sdp->device; + retval = scsi_device_get(device); if (retval) goto sg_put;

- retval = scsi_autopm_get_device(sdp->device); + retval = scsi_autopm_get_device(device); if (retval) goto sdp_put;

@@ -313,7 +315,7 @@ sg_open(struct inode *inode, struct file *filp) * check if O_NONBLOCK. Permits SCSI commands to be issued * during error recovery. Tread carefully. */ if (!((flags & O_NONBLOCK) || - scsi_block_when_processing_errors(sdp->device))) { + scsi_block_when_processing_errors(device))) { retval = -ENXIO; /* we are in error recovery for this device */ goto error_out; @@ -344,7 +346,7 @@ sg_open(struct inode *inode, struct file *filp)

if (sdp->open_cnt < 1) { /* no existing opens */ sdp->sgdebug = 0; - q = sdp->device->request_queue; + q = device->request_queue; sdp->sg_tablesize = queue_max_segments(q); } sfp = sg_add_sfp(sdp); @@ -370,10 +372,11 @@ sg_open(struct inode *inode, struct file *filp) error_mutex_locked: mutex_unlock(&sdp->open_rel_lock); error_out: - scsi_autopm_put_device(sdp->device); + scsi_autopm_put_device(device); sdp_put: - scsi_device_put(sdp->device); - goto sg_put; + kref_put(&sdp->d_ref, sg_device_destroy); + scsi_device_put(device); + return retval; }

/* Release resources associated with a successful sg_open() @@ -2233,7 +2236,6 @@ sg_remove_sfp_usercontext(struct work_struct *work) "sg_remove_sfp: sfp=0x%p\n", sfp)); kfree(sfp);

- WARN_ON_ONCE(kref_read(&sdp->d_ref) != 1); kref_put(&sdp->d_ref, sg_device_destroy); scsi_device_put(device); module_put(THIS_MODULE);