From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm: fix use-after-free when anon vma name is used after vma is freed
When adjacent vmas are being merged it can result in the vma that was
originally passed to madvise_update_vma being destroyed. In the current
implementation, the name parameter passed to madvise_update_vma points
directly to vma->anon_name and it is used after the call to vma_merge. In
the cases when vma_merge merges the original vma and destroys it, this
might result in UAF. For that the original vma would have to hold the
anon_vma_name with the last reference. The following vma would need to
contain a different anon_vma_name object with the same string. Such
scenario is shown below:
madvise_vma_behavior(vma)
madvise_update_vma(vma, ..., anon_name == vma->anon_name)
vma_merge(vma)
__vma_adjust(vma) <-- merges vma with adjacent one
vm_area_free(vma) <-- frees the original vma
replace_vma_anon_name(anon_name) <-- UAF of vma->anon_name
Fix this by raising the name refcount and stabilizing it.
Link: https://lkml.kernel.org/r/20220224231834.1481408-3-surenb@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220223153613.835563-3-surenb@xxxxxxxxxx
Fixes: 9a10064f5625 ("mm: add a field to store names for private anonymous memory")
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reported-by: syzbot+aa7b3d4b35f9dc46a366@xxxxxxxxxxxxxxxxxxxxxxxxx
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Alexey Gladkov <legion@xxxxxxxxxx>
Cc: Chris Hyser <chris.hyser@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Xiaofeng Cao <caoxiaofeng@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/madvise.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/mm/madvise.c~mm-fix-use-after-free-when-anon-vma-name-is-used-after-vma-is-freed
+++ a/mm/madvise.c
@@ -131,6 +131,8 @@ static int replace_anon_vma_name(struct
/*
* Update the vm_flags on region of a vma, splitting it or merging it as
* necessary. Must be called with mmap_sem held for writing;
+ * Caller should ensure anon_name stability by raising its refcount even when
+ * anon_name belongs to a valid vma because this function might free that vma.
*/
static int madvise_update_vma(struct vm_area_struct *vma,
struct vm_area_struct **prev, unsigned long start,
@@ -945,6 +947,7 @@ static int madvise_vma_behavior(struct v
unsigned long behavior)
{
int error;
+ struct anon_vma_name *anon_name;
unsigned long new_flags = vma->vm_flags;
switch (behavior) {
@@ -1010,8 +1013,11 @@ static int madvise_vma_behavior(struct v
break;
}
+ anon_name = anon_vma_name(vma);
+ anon_vma_name_get(anon_name);
error = madvise_update_vma(vma, prev, start, end, new_flags,
- anon_vma_name(vma));
+ anon_name);
+ anon_vma_name_put(anon_name);
out:
/*
_
