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->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 will result in use-after-free bug as shown below:
madvise_vma_behavior << passes vma->anon_name->name as name param
madvise_update_vma(name)
vma_merge
__vma_adjust
vm_area_free <-- frees the vma
replace_vma_anon_name(name) <-- UAF
Fix this by raising the name refcount and stabilizing it.
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
---
changes in v3:
- Reapplied the fix after code refactoring, per Michal Hocko
mm/madvise.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/madvise.c b/mm/madvise.c
index a395884aeecb..00e8105430e9 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -140,6 +140,8 @@ static int replace_vma_anon_name(struct vm_area_struct *vma,
/*
* 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,
@@ -1021,8 +1023,10 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
}
anon_name = vma_anon_name(vma);
+ anon_vma_name_get(anon_name);
error = madvise_update_vma(vma, prev, start, end, new_flags,
anon_name);
+ anon_vma_name_put(anon_name);
out:
/*
--
2.35.1.473.g83b2b277ed-goog
