@@ -131,6 +131,8 @@ static int replace_anon_vma_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,
@@ -945,6 +947,7 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
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 vm_area_struct *vma,
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:
/*
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/20220223153613.835563-3-surenb@google.com Fixes: 9a10064f5625 ("mm: add a field to store names for private anonymous memory") Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reported-by: syzbot+aa7b3d4b35f9dc46a366@syzkaller.appspotmail.com Acked-by: Michal Hocko <mhocko@suse.com> --- changes in v6: - Updated description clarifying the last reference requirement, per Michal Hocko - Added Ack, per Michal Hocko mm/madvise.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)