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When a UAS device is unplugged during data transfer, there is
a probability of a system panic occurring. The root cause is
an access to an invalid memory address during URB callback handling.
Specifically, this happens when the dma_direct_unmap_sg() function
is called within the usb_hcd_unmap_urb_for_dma() interface, but the
sg->dma_address field is 0 and the sg data structure has already been
freed.
The SCSI driver sends transfer commands by invoking uas_queuecommand_lck()
in uas.c, using the uas_submit_urbs() function to submit requests to USB.
Within the uas_submit_urbs() implementation, three URBs (sense_urb,
data_urb, and cmd_urb) are sequentially submitted. Device removal may
occur at any point during uas_submit_urbs execution, which may result
in URB submission failure. However, some URBs might have been successfully
submitted before the failure, and uas_submit_urbs will return the -ENODEV
error code in this case. The current error handling directly calls
scsi_done(). In the SCSI driver, this eventually triggers scsi_complete()
to invoke scsi_end_request() for releasing the sgtable. The successfully
submitted URBs, when being unlinked to giveback, call
usb_hcd_unmap_urb_for_dma() in hcd.c, leading to exceptions during sg
unmapping operations since the sg data structure has already been freed.
This patch modifies the error condition check in the uas_submit_urbs()
function. When a UAS device is removed but one or more URBs have already
been successfully submitted to USB, it avoids immediately invoking
scsi_done() and save the cmnd to devinfo->cmnd array. If the successfully
submitted URBs is completed before devinfo->resetting being set, then
the scsi_done() function will be called within uas_try_complete() after
all pending URB operations are finalized. Otherwise, the scsi_done()
function will be called within uas_zap_pending(), which is executed after
usb_kill_anchored_urbs().
The error handling only takes effect when uas_queuecommand_lck() calls
uas_submit_urbs() and returns the error value -ENODEV . In this case,
the device is disconnected, and the flow proceeds to uas_disconnect(),
where uas_zap_pending() is invoked to call uas_try_complete().
Fixes:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.