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authorRoger Pau Monné <roger.pau@citrix.com>2015-11-03 16:40:43 +0000
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2015-12-18 10:00:37 -0500
commit18779149101c0dd43ded43669ae2a92d21b6f9cb (patch)
treea247aa02c54e789146dc05dc4e1a794ad2b7c111
parent1f13d75ccb806260079e0679d55d9253e370ec8a (diff)
xen-blkback: read from indirect descriptors only once
Since indirect descriptors are in memory shared with the frontend, the frontend could alter the first_sect and last_sect values after they have been validated but before they are recorded in the request. This may result in I/O requests that overflow the foreign page, possibly overwriting local pages when the I/O request is executed. When parsing indirect descriptors, only read first_sect and last_sect once. This is part of XSA155. CC: stable@vger.kernel.org Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-rw-r--r--drivers/block/xen-blkback/blkback.c15
1 files changed, 10 insertions, 5 deletions
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index f9099940c272..41fb1a917b17 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -950,6 +950,8 @@ static int xen_blkbk_parse_indirect(struct blkif_request *req,
goto unmap;
for (n = 0, i = 0; n < nseg; n++) {
+ uint8_t first_sect, last_sect;
+
if ((n % SEGS_PER_INDIRECT_FRAME) == 0) {
/* Map indirect segments */
if (segments)
@@ -957,15 +959,18 @@ static int xen_blkbk_parse_indirect(struct blkif_request *req,
segments = kmap_atomic(pages[n/SEGS_PER_INDIRECT_FRAME]->page);
}
i = n % SEGS_PER_INDIRECT_FRAME;
+
pending_req->segments[n]->gref = segments[i].gref;
- seg[n].nsec = segments[i].last_sect -
- segments[i].first_sect + 1;
- seg[n].offset = (segments[i].first_sect << 9);
- if ((segments[i].last_sect >= (XEN_PAGE_SIZE >> 9)) ||
- (segments[i].last_sect < segments[i].first_sect)) {
+
+ first_sect = READ_ONCE(segments[i].first_sect);
+ last_sect = READ_ONCE(segments[i].last_sect);
+ if (last_sect >= (XEN_PAGE_SIZE >> 9) || last_sect < first_sect) {
rc = -EINVAL;
goto unmap;
}
+
+ seg[n].nsec = last_sect - first_sect + 1;
+ seg[n].offset = first_sect << 9;
preq->nr_sects += seg[n].nsec;
}