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Subject[PATCH 4.15 18/23] net: sched: fix use-after-free in tcf_block_put_ext
Date
4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Pirko <jiri@mellanox.com>


[ Upstream commit df45bf84e4f5a48f23d4b1a07d21d566e8b587b2 ]

Since the block is freed with last chain being put, once we reach the
end of iteration of list_for_each_entry_safe, the block may be
already freed. I'm hitting this only by creating and deleting clsact:

[ 202.171952] ==================================================================
[ 202.180182] BUG: KASAN: use-after-free in tcf_block_put_ext+0x240/0x390
[ 202.187590] Read of size 8 at addr ffff880225539a80 by task tc/796
[ 202.194508]
[ 202.196185] CPU: 0 PID: 796 Comm: tc Not tainted 4.15.0-rc2jiri+ #5
[ 202.203200] Hardware name: Mellanox Technologies Ltd. "MSN2100-CB2F"/"SA001017", BIOS 5.6.5 06/07/2016
[ 202.213613] Call Trace:
[ 202.216369] dump_stack+0xda/0x169
[ 202.220192] ? dma_virt_map_sg+0x147/0x147
[ 202.224790] ? show_regs_print_info+0x54/0x54
[ 202.229691] ? tcf_chain_destroy+0x1dc/0x250
[ 202.234494] print_address_description+0x83/0x3d0
[ 202.239781] ? tcf_block_put_ext+0x240/0x390
[ 202.244575] kasan_report+0x1ba/0x460
[ 202.248707] ? tcf_block_put_ext+0x240/0x390
[ 202.253518] tcf_block_put_ext+0x240/0x390
[ 202.258117] ? tcf_chain_flush+0x290/0x290
[ 202.262708] ? qdisc_hash_del+0x82/0x1a0
[ 202.267111] ? qdisc_hash_add+0x50/0x50
[ 202.271411] ? __lock_is_held+0x5f/0x1a0
[ 202.275843] clsact_destroy+0x3d/0x80 [sch_ingress]
[ 202.281323] qdisc_destroy+0xcb/0x240
[ 202.285445] qdisc_graft+0x216/0x7b0
[ 202.289497] tc_get_qdisc+0x260/0x560

Fix this by holding the block also by chain 0 and put chain 0
explicitly, out of the list_for_each_entry_safe loop at the very
end of tcf_block_put_ext.

Fixes: efbf78973978 ("net_sched: get rid of rcu_barrier() in tcf_block_put_ext()")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_api.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -343,23 +343,24 @@ void tcf_block_put_ext(struct tcf_block

if (!block)
return;
- /* Hold a refcnt for all chains, except 0, so that they don't disappear
+ /* Hold a refcnt for all chains, so that they don't disappear
* while we are iterating.
*/
list_for_each_entry(chain, &block->chain_list, list)
- if (chain->index)
- tcf_chain_hold(chain);
+ tcf_chain_hold(chain);

list_for_each_entry(chain, &block->chain_list, list)
tcf_chain_flush(chain);

tcf_block_offload_unbind(block, q, ei);

- /* At this point, all the chains should have refcnt >= 1. Block will be
- * freed after all chains are gone.
- */
+ /* At this point, all the chains should have refcnt >= 1. */
list_for_each_entry_safe(chain, tmp, &block->chain_list, list)
tcf_chain_put(chain);
+
+ /* Finally, put chain 0 and allow block to be freed. */
+ chain = list_first_entry(&block->chain_list, struct tcf_chain, list);
+ tcf_chain_put(chain);
}
EXPORT_SYMBOL(tcf_block_put_ext);


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