crypto: scomp - Fix off-by-one bug when calculating last page

Fix off-by-one bug in the last page calculation for src and dst.

Reported-by: Nhat Pham <[email protected]>
Fixes: 2d3553e ("crypto: scomp - Remove support for some non-trivial SG lists")
Signed-off-by: Herbert Xu <[email protected]>

Author: herbertx

crypto/scompress.c

@@ -215,8 +215,8 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
 			spage = nth_page(spage, soff / PAGE_SIZE);
 			soff = offset_in_page(soff);
 
-			n = slen / PAGE_SIZE;
-			n += (offset_in_page(slen) + soff - 1) / PAGE_SIZE;
+			n = (slen - 1) / PAGE_SIZE;
+			n += (offset_in_page(slen - 1) + soff) / PAGE_SIZE;
 			if (PageHighMem(nth_page(spage, n)) &&
 			    size_add(soff, slen) > PAGE_SIZE)
 				break;
@@ -243,9 +243,9 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
 			dpage = nth_page(dpage, doff / PAGE_SIZE);
 			doff = offset_in_page(doff);
 
-			n = dlen / PAGE_SIZE;
-			n += (offset_in_page(dlen) + doff - 1) / PAGE_SIZE;
-			if (PageHighMem(dpage + n) &&
+			n = (dlen - 1) / PAGE_SIZE;
+			n += (offset_in_page(dlen - 1) + doff) / PAGE_SIZE;
+			if (PageHighMem(nth_page(dpage, n)) &&
 			    size_add(doff, dlen) > PAGE_SIZE)
 				break;
 			dst = kmap_local_page(dpage) + doff;