Commit fc663711b944 ("scsi: core: Remove the /proc/scsi/${proc_name} directory earlier") fixed a bug related to modules loading/unloading, by adding a call to scsi_proc_hostdir_rm() on scsi_remove_host(). But that led to a potential duplicate call to the hostdir_rm() routine, since it's also called from scsi_host_dev_release(). That triggered a regression report, which was then fixed by commit be03df3d4bfe ("scsi: core: Fix a procfs host directory removal regression"). The fix just dropped the hostdir_rm() call from dev_release().

But happens that this proc directory is created on scsi_host_alloc(), and that function "pairs" with scsi_host_dev_release(), while scsi_remove_host() pairs with scsi_add_host(). In other words, it seems the reason for removing the proc directory on dev_release() was meant to cover cases in which a SCSI host structure was allocated, but the call to scsi_add_host() didn't happen. And that pattern happens to exist in some error paths, for example.

Syzkaller causes that by using USB raw gadget device, error'ing on usb-storage driver, at usb_stor_probe2(). By checking that path, we can see that the BadDevice label leads to a scsi_host_put() after a SCSI host allocation, but there's no call to scsi_add_host() in such path. That leads to messages like this in dmesg (and a leak of the SCSI host proc structure):

usb-storage 4-1:87.51: USB Mass Storage device detected proc_dir_entry 'scsi/usb-storage' already registered WARNING: CPU: 1 PID: 3519 at fs/proc/generic.c:377 proc_register+0x347/0x4e0 fs/proc/generic.c:376

The proper fix seems to still call scsi_proc_hostdir_rm() on dev_release(), but guard that with the state check for SHOST_CREATED; there is even a comment in scsi_host_dev_release() detailing that: such conditional is meant for cases where the SCSI host was allocated but there was no calls to {add,remove}_host(), like the usb-storage case.

This is what we propose here and with that, the error path of usb-storage does not trigger the warning anymore.

Reported-by: syzbot+c645abf505ed21f931b5@syzkaller.appspotmail.com Fixes: be03df3d4bfe ("scsi: core: Fix a procfs host directory removal regression") Cc: stable@vger.kernel.org Cc: Bart Van Assche bvanassche@acm.org Cc: John Garry john.g.garry@oracle.com Cc: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com Signed-off-by: Guilherme G. Piccoli gpiccoli@igalia.com ---

Hi folks, thanks in advance for reviews.

The issue with usb-storage happens upstream but despite we have a repro in the aforementioned Syzkaller report, it's only easy to reproduce the proc_dir_entry warning in a timely manner on stable right now.

The reason for that is commit 036abd614007 ("scsi: core: Introduce a new list for SCSI proc directory entries") not being present on stable. This commit (indirectly) bumps the ->present field from unsigned char to uint, and the bug reproducer shows the warning whenever such field overflows, hence it's way easier/faster to see this problem in stable, though it's present in latest v6.8.0 too.

Cheers,

Guilherme

drivers/scsi/hosts.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index d7f51b84f3c7..445f4a220df3 100644 --- a/drivers/scsi/hosts.c +++ b/drivers/scsi/hosts.c @@ -353,12 +353,13 @@ static void scsi_host_dev_release(struct device *dev)

if (shost->shost_state == SHOST_CREATED) { /* - * Free the shost_dev device name here if scsi_host_alloc() - * and scsi_host_put() have been called but neither + * Free the shost_dev device name and remove the proc host dir + * here if scsi_host_{alloc,put}() have been called but neither * scsi_host_add() nor scsi_remove_host() has been called. * This avoids that the memory allocated for the shost_dev - * name is leaked. + * name as well as the proc dir structure are leaked. */ + scsi_proc_hostdir_rm(shost->hostt); kfree(dev_name(&shost->shost_dev)); }