[PATCH 3/3] usercopy: Add find_vmap_area_try() to avoid deadlocks

Kees Cook
2022-09-16T14:02:06Z

The check_object_size() checks under CONFIG_HARDENED_USERCOPY need to be
more defensive against running from interrupt context. Use a best-effort
check for VMAP areas when running in interrupt context

Suggested-by: Matthew Wilcox <willy@infradead.org>
Link: https://lore.kernel.org/linux-mm/YyQ2CSdIJdvQPSPO@casper.infradead.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: dev@der-flo.net
Cc: linux-mm@kvack.org
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/vmalloc.h | 1 +
mm/usercopy.c | 11 ++++++++++-
mm/vmalloc.c | 11 +++++++++++
3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 096d48aa3437..c8a00f181a11 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -216,6 +216,7 @@ void free_vm_area(struct vm_struct *area);
extern struct vm_struct *remove_vm_area(const void *addr);
extern struct vm_struct *find_vm_area(const void *addr);
struct vmap_area *find_vmap_area(unsigned long addr);
+struct vmap_area *find_vmap_area_try(unsigned long addr);

static inline bool is_vm_area_hugepages(const void *addr)
{
diff --git a/mm/usercopy.c b/mm/usercopy.c
index c1ee15a98633..4a371099ac64 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -173,7 +173,16 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
}

if (is_vmalloc_addr(ptr)) {
- struct vmap_area *area = find_vmap_area(addr);
+ struct vmap_area *area;
+
+ if (unlikely(in_interrupt())) {
+ area = find_vmap_area_try(addr);
+ /* Give up under interrupt to avoid deadlocks. */
+ if (!area)
+ return;
+ } else {
+ area = find_vmap_area(addr);
+ }

if (!area)
usercopy_abort("vmalloc", "no area", to_user, 0, n);
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index dd6cdb201195..f14f1902c2f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1840,6 +1840,17 @@ struct vmap_area *find_vmap_area(unsigned long addr)
return va;
}

+struct vmap_area *find_vmap_area_try(unsigned long addr)
+{
+ struct vmap_area *va = NULL;
+
+ if (spin_trylock(&vmap_area_lock)) {
+ va = __find_vmap_area(addr, &vmap_area_root);
+ spin_unlock(&vmap_area_lock);
+ }
+ return va;
+}
+
/*** Per cpu kva allocator ***/

/*
--
2.34.1