lib/scatterlist: Fix mapping iterator when sg->offset is greater than PAGE_SIZE

BugLink: https://bugs.launchpad.net/bugs/1839036
commit aeb87246537a83c2aff482f3f34a2e0991e02cbc upstream.

All mapping iterator logic is based on the assumption that sg->offset
is always lower than PAGE_SIZE.

But there are situations where sg->offset is such that the SG item
is on the second page. In that case sg_copy_to_buffer() fails
properly copying the data into the buffer. One of the reason is
that the data will be outside the kmapped area used to access that
data.

This patch fixes the issue by adjusting the mapping iterator
offset and pgoffset fields such that offset is always lower than
PAGE_SIZE.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Fixes: 4225fc8555a9 ("lib/scatterlist: use page iterator in the mapping iterator")
Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 7c1c55f7daaa832df2aef731cd218d4ed80f44dc..4c87fb589667eda3554e468d8e174eed7958902e 100644 (file)
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -537,17 +537,18 @@ static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
 {
        if (!miter->__remaining) {
                struct scatterlist *sg;
-               unsigned long pgoffset;
 
                if (!__sg_page_iter_next(&miter->piter))
                        return false;
 
                sg = miter->piter.sg;
-               pgoffset = miter->piter.sg_pgoffset;
 
-               miter->__offset = pgoffset ? 0 : sg->offset;
+               miter->__offset = miter->piter.sg_pgoffset ? 0 : sg->offset;
+               miter->piter.sg_pgoffset += miter->__offset >> PAGE_SHIFT;
+               miter->__offset &= PAGE_SIZE - 1;
                miter->__remaining = sg->offset + sg->length -
-                               (pgoffset << PAGE_SHIFT) - miter->__offset;
+                                    (miter->piter.sg_pgoffset << PAGE_SHIFT) -
+                                    miter->__offset;
                miter->__remaining = min_t(unsigned long, miter->__remaining,
                                           PAGE_SIZE - miter->__offset);
        }