Re: [PATCH][next] net: dsa: sja1105: remove redundant re-assignment of pointer table
From: Vladimir Oltean <olteanv@gmail.com>
Date: 2021-07-22 20:05:56
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kernel-janitors, lkml
On Thu, Jul 22, 2021 at 08:15:29PM +0100, Colin King wrote:
quoted hunk ↗ jump to hunk
From: Colin Ian King <redacted> The pointer table is being re-assigned with a value that is never read. The assignment is redundant and can be removed. Addresses-Coverity: ("Unused value") Signed-off-by: Colin Ian King <redacted> --- drivers/net/dsa/sja1105/sja1105_main.c | 2 -- 1 file changed, 2 deletions(-)diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c index 6618abba23b3..c65dba3111d7 100644 --- a/drivers/net/dsa/sja1105/sja1105_main.c +++ b/drivers/net/dsa/sja1105/sja1105_main.c@@ -2157,8 +2157,6 @@ static int sja1105_build_vlan_table(struct sja1105_private *priv) if (!new_vlan) return -ENOMEM; - table = &priv->static_config.tables[BLK_IDX_VLAN_LOOKUP]; - for (i = 0; i < VLAN_N_VID; i++) new_vlan[i].vlanid = VLAN_N_VID;-- 2.31.1
Oh my, what an interesting bug you uncovered.
That duplicate assignment was introduced in commit 3f01c91aab92 ("net:
dsa: sja1105: implement VLAN retagging for dsa_8021q sub-VLANs") and
used to read:
table = &priv->static_config.tables[BLK_IDX_VLAN_LOOKUP];
new_retagging = kcalloc(SJA1105_MAX_RETAGGING_COUNT,
table->ops->unpacked_entry_size, GFP_KERNEL);
In retrospect, it should have been:
table = &priv->static_config.tables[BLK_IDX_RETAGGING];
because we must allocate SJA1105_MAX_RETAGGING_COUNT elements of the
size of one VLAN retagging entry, and not of one VLAN lookup entry.
In commit 0fac6aa098ed ("net: dsa: sja1105: delete the
best_effort_vlan_filtering mode") I deleted everything that had to do
with VLAN retagging but left this behind because it didn't say RETAGGING
on it.
[BLK_IDX_VLAN_LOOKUP] = {
.unpacked_entry_size = sizeof(struct sja1105_vlan_lookup_entry),
},
[BLK_IDX_RETAGGING] = {
.unpacked_entry_size = sizeof(struct sja1105_retagging_entry),
},
and if you look at them, struct sja1105_retagging_entry has 7 u64
fields, while struct sja1105_vlan_lookup_entry has 6 elements (actually
since commit 3e77e59bf8cf ("net: dsa: sja1105: add support for the
SJA1110 switch family") it also has 7.
The point is, between commit 3f01c91aab92 and commit 3e77e59bf8cf, the
driver allocated 8 bytes too few per VLAN retagging entry, or multiplied
by 32 (the value of SJA1105_MAX_RETAGGING_COUNT), it only allocates
enough memory for 27.4 VLAN retagging entries. So any attempt to access
VLAN retagging entries 27-31 in this function would trigger an out of
bounds memory access.
Could you please also send a patch for the "net" tree with this, and the
explanation above?
- table = &priv->static_config.tables[BLK_IDX_VLAN_LOOKUP];
+ table = &priv->static_config.tables[BLK_IDX_RETAGGING];
Thanks.