[PATCH 5.5 362/399] char: hpet: Fix out-of-bounds read bug

[Greg Kroah-Hartman]

From: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

[ Upstream commit 98c49f1746ac44ccc164e914b9a44183fad09f51 ]

Currently, there is an out-of-bounds read on array hpetp->hp_dev
in the following for loop:

870         for (i = 0; i < hdp->hd_nirqs; i++)
871                 hpetp->hp_dev[i].hd_hdwirq = hdp->hd_irq[i];

This is due to the recent change from one-element array to
flexible-array member in struct hpets:

104 struct hpets {
	...
113         struct hpet_dev hp_dev[];
114 };

This change affected the total size of the dynamic memory
allocation, decreasing it by one time the size of struct hpet_dev.

Fix this by adjusting the allocation size when calling
struct_size().

Fixes: 987f028b8637c ("char: hpet: Use flexible-array member")
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Acked-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200129022613.GA24281@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/char/hpet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 9ac6671bb5141..f69609b47fef8 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -855,7 +855,7 @@ int hpet_alloc(struct hpet_data *hdp)
 		return 0;
 	}
 
-	hpetp = kzalloc(struct_size(hpetp, hp_dev, hdp->hd_nirqs - 1),
+	hpetp = kzalloc(struct_size(hpetp, hp_dev, hdp->hd_nirqs),
 			GFP_KERNEL);
 
 	if (!hpetp)
-- 
2.20.1