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author | Daniel Borkmann <daniel@iogearbox.net> | 2024-07-08 16:31:29 +0300 |
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committer | Martin KaFai Lau <martin.lau@kernel.org> | 2024-07-09 00:07:31 +0300 |
commit | 1cb6f0bae50441f4b4b32a28315853b279c7404e (patch) | |
tree | 2a77853cb7254aed5df87823ba5a216b23c17158 /include/net | |
parent | 83c36e7cfd74e41a5c145640dba581b38f12aa15 (diff) | |
download | linux-1cb6f0bae50441f4b4b32a28315853b279c7404e.tar.xz |
bpf: Fix too early release of tcx_entry
Pedro Pinto and later independently also Hyunwoo Kim and Wongi Lee reported
an issue that the tcx_entry can be released too early leading to a use
after free (UAF) when an active old-style ingress or clsact qdisc with a
shared tc block is later replaced by another ingress or clsact instance.
Essentially, the sequence to trigger the UAF (one example) can be as follows:
1. A network namespace is created
2. An ingress qdisc is created. This allocates a tcx_entry, and
&tcx_entry->miniq is stored in the qdisc's miniqp->p_miniq. At the
same time, a tcf block with index 1 is created.
3. chain0 is attached to the tcf block. chain0 must be connected to
the block linked to the ingress qdisc to later reach the function
tcf_chain0_head_change_cb_del() which triggers the UAF.
4. Create and graft a clsact qdisc. This causes the ingress qdisc
created in step 1 to be removed, thus freeing the previously linked
tcx_entry:
rtnetlink_rcv_msg()
=> tc_modify_qdisc()
=> qdisc_create()
=> clsact_init() [a]
=> qdisc_graft()
=> qdisc_destroy()
=> __qdisc_destroy()
=> ingress_destroy() [b]
=> tcx_entry_free()
=> kfree_rcu() // tcx_entry freed
5. Finally, the network namespace is closed. This registers the
cleanup_net worker, and during the process of releasing the
remaining clsact qdisc, it accesses the tcx_entry that was
already freed in step 4, causing the UAF to occur:
cleanup_net()
=> ops_exit_list()
=> default_device_exit_batch()
=> unregister_netdevice_many()
=> unregister_netdevice_many_notify()
=> dev_shutdown()
=> qdisc_put()
=> clsact_destroy() [c]
=> tcf_block_put_ext()
=> tcf_chain0_head_change_cb_del()
=> tcf_chain_head_change_item()
=> clsact_chain_head_change()
=> mini_qdisc_pair_swap() // UAF
There are also other variants, the gist is to add an ingress (or clsact)
qdisc with a specific shared block, then to replace that qdisc, waiting
for the tcx_entry kfree_rcu() to be executed and subsequently accessing
the current active qdisc's miniq one way or another.
The correct fix is to turn the miniq_active boolean into a counter. What
can be observed, at step 2 above, the counter transitions from 0->1, at
step [a] from 1->2 (in order for the miniq object to remain active during
the replacement), then in [b] from 2->1 and finally [c] 1->0 with the
eventual release. The reference counter in general ranges from [0,2] and
it does not need to be atomic since all access to the counter is protected
by the rtnl mutex. With this in place, there is no longer a UAF happening
and the tcx_entry is freed at the correct time.
Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support")
Reported-by: Pedro Pinto <xten@osec.io>
Co-developed-by: Pedro Pinto <xten@osec.io>
Signed-off-by: Pedro Pinto <xten@osec.io>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Hyunwoo Kim <v4bel@theori.io>
Cc: Wongi Lee <qwerty@theori.io>
Cc: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240708133130.11609-1-daniel@iogearbox.net
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Diffstat (limited to 'include/net')
-rw-r--r-- | include/net/tcx.h | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/include/net/tcx.h b/include/net/tcx.h index 72a3e75e539f..5ce0ce9e0c02 100644 --- a/include/net/tcx.h +++ b/include/net/tcx.h @@ -13,7 +13,7 @@ struct mini_Qdisc; struct tcx_entry { struct mini_Qdisc __rcu *miniq; struct bpf_mprog_bundle bundle; - bool miniq_active; + u32 miniq_active; struct rcu_head rcu; }; @@ -125,11 +125,16 @@ static inline void tcx_skeys_dec(bool ingress) tcx_dec(); } -static inline void tcx_miniq_set_active(struct bpf_mprog_entry *entry, - const bool active) +static inline void tcx_miniq_inc(struct bpf_mprog_entry *entry) { ASSERT_RTNL(); - tcx_entry(entry)->miniq_active = active; + tcx_entry(entry)->miniq_active++; +} + +static inline void tcx_miniq_dec(struct bpf_mprog_entry *entry) +{ + ASSERT_RTNL(); + tcx_entry(entry)->miniq_active--; } static inline bool tcx_entry_is_active(struct bpf_mprog_entry *entry) |