mm, gup: add missing refcount overflow checks on x86 and s390
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from
overflowing page refcount") was backported to 4.9.y stable as commit
2ed768cfd895. The backport however missed that in 4.9, there are several
arch-specific gup.c versions with fast gup implementations, so these do not
prevent refcount overflow.
This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm,
gup: prevent get_page() race with munmap in paravirt guest"). This stable-only
commit adds missing parts to x86 version, as well as s390 version, both taken
from the SUSE SLES/openSUSE 4.12-based kernels.
The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely
the known overflow scenario based on FUSE, which needs 140GB of RAM, is a
problem for those architectures, and I don't feel confident enough to patch
them.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 97fc449..cf045f5 100644
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -38,7 +38,8 @@
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
head = compound_head(page);
- if (!page_cache_get_speculative(head))
+ if (WARN_ON_ONCE(page_ref_count(head) < 0)
+ || !page_cache_get_speculative(head))
return 0;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(head);
@@ -76,7 +77,8 @@
refs++;
} while (addr += PAGE_SIZE, addr != end);
- if (!page_cache_add_speculative(head, refs)) {
+ if (WARN_ON_ONCE(page_ref_count(head) < 0)
+ || !page_cache_add_speculative(head, refs)) {
*nr -= refs;
return 0;
}
@@ -150,7 +152,8 @@
refs++;
} while (addr += PAGE_SIZE, addr != end);
- if (!page_cache_add_speculative(head, refs)) {
+ if (WARN_ON_ONCE(page_ref_count(head) < 0)
+ || !page_cache_add_speculative(head, refs)) {
*nr -= refs;
return 0;
}