CVE-2024-26935

In the Linux kernel, the following vulnerability has been resolved:

scsi: core: Fix unremoved procfs host directory regression

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 its 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 it 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() didnt happen. And that pattern happens to exist in some error paths, for example.

Syzkaller causes that by using USB raw gadget device, erroring 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 theres 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.

Affected Software

References

• https://git.kernel.org/stable/c/0053f15d50d50c9312d8ab9c11e2e405812dfcac
• https://git.kernel.org/stable/c/3678cf67ff7136db1dd3bf63c361650db5d92889
• https://git.kernel.org/stable/c/5c2386ba80e779a92ec3bb64ccadbedd88f779b1
• https://git.kernel.org/stable/c/cea234bb214b17d004dfdccce4491e6ff57c96ee
• https://git.kernel.org/stable/c/d4c34782b6d7b1e68d18d9549451b19433bd4c6c
• https://git.kernel.org/stable/c/e293c773c13b830cdc251f155df2254981abc320
• https://git.kernel.org/stable/c/f23a4d6e07570826fe95023ca1aa96a011fa9f84
• https://git.kernel.org/stable/c/f4ff08fab66eb5c0b97e1a24edac052fb40bf5d7