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scsi: sg: recheck MMAP_IO request length with lock held 

Commit 1bc0eb0446 ("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>
This commit is contained in:
Todd Poynor 2017-08-15 21:48:43 -07:00 committed by Martin K. Petersen
parent 55e1f9f088
commit 8d26f49111
1 changed files with 5 additions and 2 deletions
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7
drivers/scsi/sg.c
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@ -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) {