The patch titled
Subject: mm: vmalloc: prevent use after free in _vm_unmap_aliases
has been added to the -mm tree. Its filename is
mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases.patch
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------------------------------------------------------
From: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Subject: mm: vmalloc: prevent use after free in _vm_unmap_aliases
A potential use after free can occur in _vm_unmap_aliases where an already
freed vmap_area could be accessed, Consider the following scenario:
Process 1 Process 2
__vm_unmap_aliases __vm_unmap_aliases
purge_fragmented_blocks_allcpus rcu_read_lock()
rcu_read_lock()
list_del_rcu(&vb->free_list)
list_for_each_entry_rcu(vb .. )
__purge_vmap_area_lazy
kmem_cache_free(va)
va_start = vb->va->va_start
Here Process 1 is in purge path and it does list_del_rcu on vmap_block and
later frees the vmap_area, since Process 2 was holding the rcu lock at
this time vmap_block will still be present in and Process 2 accesse it and
thereby it tries to access vmap_area of that vmap_block which was already
freed by Process 1 and this results in use after free.
Fix this by adding a check for vb->dirty before accessing vmap_area
structure since vb->dirty will be set to VMAP_BBMAP_BITS in purge path
checking for this will prevent the use after free.
Link: https://lkml.kernel.org/r/1616062105-23263-1-git-send-email-vjitta@xxxxxxxxxxxxxx
Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/vmalloc.c~mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases
+++ a/mm/vmalloc.c
@@ -2039,7 +2039,7 @@ static void _vm_unmap_aliases(unsigned l
rcu_read_lock();
list_for_each_entry_rcu(vb, &vbq->free, free_list) {
spin_lock(&vb->lock);
- if (vb->dirty) {
+ if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
unsigned long va_start = vb->va->va_start;
unsigned long s, e;
_
Patches currently in -mm which might be from vjitta@xxxxxxxxxxxxxx are
mm-vmalloc-prevent-use-after-free-in-_vm_unmap_aliases.patch
