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mt76: mt7915: fix a couple information leaks

PATCH In review Dan Carpenter 3 participants 4 messages Jan 7, 2022

Subsystems (3)
Kernel janitors Arm MediaTek MediaTek MT76 wireless LAN driver
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Dan Carpenter

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#0 lore raw

PATCH 1/1 mt76: mt7915: fix a couple information leaks

Unfortunately this code has stumbled into some deep C standards nonsense. These two structs have a 3 byte struct hole at the end. If you partially initialize a struct then the C standard specifies that all the struct holes are zeroed out. But when you initialize all the members of the struct, as this code does, then struct holes may be left with uninitialized stack data. This is from C11 section 6.7.9 and how it is implemented in GCC.

Anyway, add some memsets to prevent exposing uninitialized stack data with the user. Debugfs is root only so the real life impact of these leaks is very small.

Fixes 1966a5078f2d ("mt76: mt7915: add mu-mimo and ofdma debugfs knobs")
Signed-off-by Dan Carpenter <[email protected]>
---
 .../net/wireless/mediatek/mt76/mt7915/mcu.c   | 21 ++++++++++---------
 1 file changed, 11 insertions(+), 10 deletions(-)
drivers/net/wireless/mediatek/mt76/mt7915/mcu.c +11 -10
index 0911b6f973b5..19c340c65465 100644
@@ -2999,10 +2999,11 @@ int mt7915_mcu_muru_debug_set(struct mt7915_dev *dev, bool enabled)
 	struct {
 		__le32 cmd;
 		u8 enable;
-	} data = {
-		.cmd = cpu_to_le32(MURU_SET_TXC_TX_STATS_EN),
-		.enable = enabled,
-	};
+	} data;
+
+	memset(&data, 0, sizeof(data));
+	data.cmd = cpu_to_le32(MURU_SET_TXC_TX_STATS_EN);
+	data.enable = enabled;
 
 	return mt76_mcu_send_msg(&dev->mt76, MCU_EXT_CMD(MURU_CTRL), &data,
 				sizeof(data), false);

@@ -3014,15 +3015,15 @@ int mt7915_mcu_muru_debug_get(struct mt7915_phy *phy, void *ms)
 	struct sk_buff *skb;
 	struct mt7915_mcu_muru_stats *mu_stats =
 				(struct mt7915_mcu_muru_stats *)ms;
-	int ret;
-
 	struct {
 		__le32 cmd;
 		u8 band_idx;
-	} req = {
-		.cmd = cpu_to_le32(MURU_GET_TXC_TX_STATS),
-		.band_idx = phy != &dev->phy,
-	};
+	} req;
+	int ret;
+
+	memset(&req, 0, sizeof(req));
+	req.cmd = cpu_to_le32(MURU_GET_TXC_TX_STATS);
+	req.band_idx = phy != &dev->phy;
 
 	ret = mt76_mcu_send_and_get_msg(&dev->mt76, MCU_EXT_CMD(MURU_CTRL),
 					&req, sizeof(req), true, &skb);
Signature · 1 line
2.20.1
#1 lore raw
Quoted 7 lines · Dan Carpenter

Unfortunately this code has stumbled into some deep C standards nonsense. These two structs have a 3 byte struct hole at the end. If you partially initialize a struct then the C standard specifies that all the struct holes are zeroed out. But when you initialize all the members of the struct, as this code does, then struct holes may be left with uninitialized stack data. This is from C11 section 6.7.9 and how it is implemented in GCC.

Wow, nice find ...

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c int mt7915_mcu_muru_debug_set(struct mt7915_dev *dev, bool enabled) · line 3006

Quoted 4 lines
drivers/net/wireless/mediatek/mt76/mt7915/mcu.c +3 -0
+	memset(&data, 0, sizeof(data));
+	data.cmd = cpu_to_le32(MURU_SET_TXC_TX_STATS_EN);
+	data.enable = enabled;

Maybe add a comment? This is not going to be obvious in the future.

Quoted 3 lines

return mt76_mcu_send_msg(&dev->mt76, MCU_EXT_CMD(MURU_CTRL),
&data,
sizeof(data), false);

Or maybe instead just mark the thing __packed (and/or explicitly add the padding if needed), it seems weird that we'd send something to the *firmware* that has a struct layout subject to compiler/arch padding rules.

johannes

maintainer
#2 lore raw
Quoted 18 lines · Johannes Berg
Quoted 7 lines · Dan Carpenter

Unfortunately this code has stumbled into some deep C standards nonsense. These two structs have a 3 byte struct hole at the end. If you partially initialize a struct then the C standard specifies that all the struct holes are zeroed out. But when you initialize all the members of the struct, as this code does, then struct holes may be left with uninitialized stack data. This is from C11 section 6.7.9 and how it is implemented in GCC.

Wow, nice find ...

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c int mt7915_mcu_muru_debug_set(struct mt7915_dev *dev, bool enabled) · line 3006

Quoted 4 lines
drivers/net/wireless/mediatek/mt76/mt7915/mcu.c +3 -0
+	memset(&data, 0, sizeof(data));
+	data.cmd = cpu_to_le32(MURU_SET_TXC_TX_STATS_EN);
+	data.enable = enabled;

Maybe add a comment? This is not going to be obvious in the future.

Quoted 8 lines
Quoted 3 lines

return mt76_mcu_send_msg(&dev->mt76, MCU_EXT_CMD(MURU_CTRL),
&data,
sizeof(data), false);

Or maybe instead just mark the thing __packed (and/or explicitly add the padding if needed), it seems weird that we'd send something to the *firmware* that has a struct layout subject to compiler/arch padding rules.

I would also prefer explicitly adding the padding and leaving the rest of the code as-is.

- Felix

#3 lore raw
Quoted 8 lines · Felix Fietkau
Quoted 5 lines

Or maybe instead just mark the thing __packed (and/or explicitly add the padding if needed), it seems weird that we'd send something to the *firmware* that has a struct layout subject to compiler/arch padding rules.

I would also prefer explicitly adding the padding and leaving the rest of the code as-is.

Arguably, if you add padding explicitly, you might want to also mark it __packed or add some BUILD_BUG_ON() ensuring there's no more padding added by the compiler because of weird architectures, or whatnot?

johannes