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@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: be03df3d4bfe ("scsi: core: Fix a procfs host directory removal regression")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: John Garry <john.g.garry@xxxxxxxxxx>
Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
---
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));
}
--
2.43.0
