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Message-Id: <20200125210111.22058-1-olteanv@gmail.com>
Date: Sat, 25 Jan 2020 23:01:11 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: f.fainelli@...il.com, vivien.didelot@...il.com, andrew@...n.ch,
davem@...emloft.net
Cc: netdev@...r.kernel.org, marek.behun@....cz,
Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net] net: dsa: Fix use-after-free in probing of DSA switch tree
From: Vladimir Oltean <vladimir.oltean@....com>
DSA sets up a switch tree little by little. Every switch of the N
members of the tree calls dsa_register_switch, and (N - 1) will just
touch the dst->ports list with their ports and quickly exit. Only the
last switch that calls dsa_register_switch will find all DSA links
complete in dsa_tree_setup_routing_table, and not return zero as a
result but instead go ahead and set up the entire DSA switch tree
(practically on behalf of the other switches too).
The trouble is that the (N - 1) switches don't clean up after themselves
after they get an error such as EPROBE_DEFER. Their footprint left in
dst->ports by dsa_switch_touch_ports is still there. And switch N, the
one responsible with actually setting up the tree, is going to work with
those stale dp, dp->ds and dp->ds->dev pointers. In particular ds and
ds->dev might get freed by the device driver.
Be there a 2-switch tree and the following calling order:
- Switch 1 calls dsa_register_switch
- Calls dsa_switch_touch_ports, populates dst->ports
- Calls dsa_port_parse_cpu, gets -EPROBE_DEFER, exits.
- Switch 2 calls dsa_register_switch
- Calls dsa_switch_touch_ports, populates dst->ports
- Probe doesn't get deferred, so it goes ahead.
- Calls dsa_tree_setup_routing_table, which returns "complete == true"
due to Switch 1 having called dsa_switch_touch_ports before.
- Because the DSA links are complete, it calls dsa_tree_setup_switches
now.
- dsa_tree_setup_switches iterates through dst->ports, initializing
the Switch 1 ds structure (invalid) and the Switch 2 ds structure
(valid).
- Undefined behavior (use after free, sometimes NULL pointers, etc).
Real example below (debugging prints added by me, as well as guards
against NULL pointers):
[ 5.477947] dsa_tree_setup_switches: Setting up port 0 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.313002] dsa_tree_setup_switches: Setting up port 1 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.319932] dsa_tree_setup_switches: Setting up port 2 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.329693] dsa_tree_setup_switches: Setting up port 3 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.339458] dsa_tree_setup_switches: Setting up port 4 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.349226] dsa_tree_setup_switches: Setting up port 5 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.358991] dsa_tree_setup_switches: Setting up port 6 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.368758] dsa_tree_setup_switches: Setting up port 7 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.378524] dsa_tree_setup_switches: Setting up port 8 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.388291] dsa_tree_setup_switches: Setting up port 9 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.398057] dsa_tree_setup_switches: Setting up port 10 of switch ffffff803df0b980 (dev ffffff803f775c00)
[ 6.407912] dsa_tree_setup_switches: Setting up port 0 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.417682] dsa_tree_setup_switches: Setting up port 1 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.427446] dsa_tree_setup_switches: Setting up port 2 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.437212] dsa_tree_setup_switches: Setting up port 3 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.446979] dsa_tree_setup_switches: Setting up port 4 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.456744] dsa_tree_setup_switches: Setting up port 5 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.466512] dsa_tree_setup_switches: Setting up port 6 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.476277] dsa_tree_setup_switches: Setting up port 7 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.486043] dsa_tree_setup_switches: Setting up port 8 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.495810] dsa_tree_setup_switches: Setting up port 9 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.505577] dsa_tree_setup_switches: Setting up port 10 of switch ffffff803da02f80 (dev 0000000000000000)
[ 6.515433] dsa_tree_setup_switches: Setting up port 0 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.354120] dsa_tree_setup_switches: Setting up port 1 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.361045] dsa_tree_setup_switches: Setting up port 2 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.370805] dsa_tree_setup_switches: Setting up port 3 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.380571] dsa_tree_setup_switches: Setting up port 4 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.390337] dsa_tree_setup_switches: Setting up port 5 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.400104] dsa_tree_setup_switches: Setting up port 6 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.409872] dsa_tree_setup_switches: Setting up port 7 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.419637] dsa_tree_setup_switches: Setting up port 8 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.429403] dsa_tree_setup_switches: Setting up port 9 of switch ffffff803db15b80 (dev ffffff803d8e4800)
[ 7.439169] dsa_tree_setup_switches: Setting up port 10 of switch ffffff803db15b80 (dev ffffff803d8e4800)
The solution is to recognize that the functions that call
dsa_switch_touch_ports (dsa_switch_parse_of, dsa_switch_parse) have side
effects, and therefore one should clean up their side effects on error
path. The cleanup of dst->ports was taken from dsa_switch_remove and
moved into a dedicated dsa_switch_release_ports function, which should
really be per-switch (free only the members of dst->ports that are also
members of ds, instead of all switch ports).
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
Sadly I really have no clue how/if this was supposed to work, and I
can't provide a meaningful Fixes: tag. The board I have doesn't appear
to boot on older versions of the kernel if I try to bisect this.
net/dsa/dsa2.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index c6d81f2baf4e..e7c30b472034 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -849,6 +849,19 @@ static int dsa_switch_parse(struct dsa_switch *ds, struct dsa_chip_data *cd)
return dsa_switch_parse_ports(ds, cd);
}
+static void dsa_switch_release_ports(struct dsa_switch *ds)
+{
+ struct dsa_switch_tree *dst = ds->dst;
+ struct dsa_port *dp, *next;
+
+ list_for_each_entry_safe(dp, next, &dst->ports, list) {
+ if (dp->ds != ds)
+ continue;
+ list_del(&dp->list);
+ kfree(dp);
+ }
+}
+
static int dsa_switch_probe(struct dsa_switch *ds)
{
struct dsa_switch_tree *dst;
@@ -865,12 +878,17 @@ static int dsa_switch_probe(struct dsa_switch *ds)
if (!ds->num_ports)
return -EINVAL;
- if (np)
+ if (np) {
err = dsa_switch_parse_of(ds, np);
- else if (pdata)
+ if (err)
+ dsa_switch_release_ports(ds);
+ } else if (pdata) {
err = dsa_switch_parse(ds, pdata);
- else
+ if (err)
+ dsa_switch_release_ports(ds);
+ } else {
err = -ENODEV;
+ }
if (err)
return err;
@@ -878,8 +896,10 @@ static int dsa_switch_probe(struct dsa_switch *ds)
dst = ds->dst;
dsa_tree_get(dst);
err = dsa_tree_setup(dst);
- if (err)
+ if (err) {
+ dsa_switch_release_ports(ds);
dsa_tree_put(dst);
+ }
return err;
}
@@ -900,15 +920,9 @@ EXPORT_SYMBOL_GPL(dsa_register_switch);
static void dsa_switch_remove(struct dsa_switch *ds)
{
struct dsa_switch_tree *dst = ds->dst;
- struct dsa_port *dp, *next;
dsa_tree_teardown(dst);
-
- list_for_each_entry_safe(dp, next, &dst->ports, list) {
- list_del(&dp->list);
- kfree(dp);
- }
-
+ dsa_switch_release_ports(ds);
dsa_tree_put(dst);
}
--
2.17.1
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