Re: [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
> > On 3/18/2021 10:29 PM, Uladzislau Rezki wrote: > > On Thu, Mar 18, 2021 at 03:38:25PM +0530, vji...@codeaurora.org wrote: > >> From: Vijayanand Jitta > >> > >> 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(>free_list) > >> > >> list_for_each_entry_rcu(vb .. ) > >>__purge_vmap_area_lazy > >>kmem_cache_free(va) > >> > >> va_start = vb->va->va_start > > Or maybe we should switch to kfree_rcu() instead of kmem_cache_free()? > > > > -- > > Vlad Rezki > > > > Thanks for suggestion. > > I see free_vmap_area_lock (spinlock) is taken in __purge_vmap_area_lazy > while it loops through list and calls kmem_cache_free on va's. So, looks > like we can't replace it with kfree_rcu as it might cause scheduling > within atomic context. > A double argument of the kfree_rcu() is a safe way to be used from atomic contexts, it does not use any sleeping primitives, so it can be replaced. >From the other hand i see that per-cpu KVA allocator is only one user of the RCU and your change fixes it. Feel free to use: Reviewed-by: Uladzislau Rezki (Sony) Thanks. -- Vlad Rezki
Re: [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
On 3/18/2021 10:29 PM, Uladzislau Rezki wrote: > On Thu, Mar 18, 2021 at 03:38:25PM +0530, vji...@codeaurora.org wrote: >> From: Vijayanand Jitta >> >> 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 1Process 2 >> >> __vm_unmap_aliases __vm_unmap_aliases >> purge_fragmented_blocks_allcpus rcu_read_lock() >> rcu_read_lock() >> list_del_rcu(>free_list) >> >> list_for_each_entry_rcu(vb .. ) >> __purge_vmap_area_lazy >> kmem_cache_free(va) >> >> va_start = vb->va->va_start > Or maybe we should switch to kfree_rcu() instead of kmem_cache_free()? > > -- > Vlad Rezki > Thanks for suggestion. I see free_vmap_area_lock (spinlock) is taken in __purge_vmap_area_lazy while it loops through list and calls kmem_cache_free on va's. So, looks like we can't replace it with kfree_rcu as it might cause scheduling within atomic context. Thanks, Vijay -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
Re: [PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
On Thu, Mar 18, 2021 at 03:38:25PM +0530, vji...@codeaurora.org wrote: > From: Vijayanand Jitta > > 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(>free_list) > > list_for_each_entry_rcu(vb .. ) > __purge_vmap_area_lazy > kmem_cache_free(va) > > va_start = vb->va->va_start Or maybe we should switch to kfree_rcu() instead of kmem_cache_free()? -- Vlad Rezki
[PATCH] mm: vmalloc: Prevent use after free in _vm_unmap_aliases
From: Vijayanand Jitta
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(>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.
Signed-off-by: Vijayanand Jitta
---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d5f2a84..ebb6f57 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1762,7 +1762,7 @@ static void _vm_unmap_aliases(unsigned long start,
unsigned long end, int flush)
rcu_read_lock();
list_for_each_entry_rcu(vb, >free, free_list) {
spin_lock(>lock);
- if (vb->dirty) {
+ if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
unsigned long va_start = vb->va->va_start;
unsigned long s, e;
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
Code Aurora Forum, hosted by The Linux Foundation
2.7.4
