Commit 8d26f491 authored Aug 15, 2017 by Todd Poynor Committed by Martin K. Petersen Aug 24, 2017

scsi: sg: recheck MMAP_IO request length with lock held



Commit 1bc0eb04 ("scsi: sg: protect accesses to 'reserved' page
array") adds needed concurrency protection for the "reserve" buffer.
Some checks that are initially made outside the lock are replicated once
the lock is taken to ensure the checks and resulting decisions are made
using consistent state.

The check that a request with flag SG_FLAG_MMAP_IO set fits in the
reserve buffer also needs to be performed again under the lock to ensure
the reserve buffer length compared against matches the value in effect
when the request is linked to the reserve buffer.  An -ENOMEM should be
returned in this case, instead of switching over to an indirect buffer
as for non-MMAP_IO requests.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

parent 55e1f9f0

drivers/scsi/sg.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -1764,9 +1764,12 @@ sg_start_req(Sg_request srp, unsigned char cmd)
		!sfp->res_in_use) {
		sfp->res_in_use = 1;
		sg_link_reserve(sfp, srp, dxfer_len);
		} else if ((hp->flags & SG_FLAG_MMAP_IO) && sfp->res_in_use) {
		} else if (hp->flags & SG_FLAG_MMAP_IO) {
		res = -EBUSY; /* sfp->res_in_use == 1 */
		if (dxfer_len > rsv_schp->bufflen)
		res = -ENOMEM;
		mutex_unlock(&sfp->f_mutex);
		return -EBUSY;
		return res;
		} else {
		res = sg_build_indirect(req_schp, sfp, dxfer_len);
		if (res) {

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