3.13.11-ckt33 -stable review patch. If anyone has any objections, please let me know.
---8<------------------------------------------------------------ From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <[email protected]> commit 18779149101c0dd43ded43669ae2a92d21b6f9cb upstream. 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. Signed-off-by: Roger Pau Monné <[email protected]> Signed-off-by: David Vrabel <[email protected]> Signed-off-by: Konrad Rzeszutek Wilk <[email protected]> [ luis: backported to 3.16: - Use ACCESS_ONCE instead of READ_ONCE - Use PAGE_SIZE instead of XEN_PAGE_SIZE ] Signed-off-by: Luis Henriques <[email protected]> Signed-off-by: Kamal Mostafa <[email protected]> --- drivers/block/xen-blkback/blkback.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index 08c8185..0219bf2 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -853,6 +853,8 @@ 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) @@ -860,15 +862,18 @@ 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 >= (PAGE_SIZE >> 9)) || - (segments[i].last_sect < segments[i].first_sect)) { + + first_sect = ACCESS_ONCE(segments[i].first_sect); + last_sect = ACCESS_ONCE(segments[i].last_sect); + if (last_sect >= (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; } -- 1.9.1
