[PATCH 4.4 060/131] stm class: Prevent user-controllable allocations

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit f08b18266c7116e2ec6885dd53a928f580060a71 ]

Currently, the character device write method allocates a temporary buffer
for user's data, but the user's data size is not sanitized and can cause
arbitrarily large allocations via kzalloc() or an integer overflow that
will then result in overwriting kernel memory.

This patch trims the input buffer size to avoid these issues.

Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/hwtracing/stm/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index f286de2e86af..e4fa583b57a6 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -410,6 +410,9 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 	char *kbuf;
 	int err;
 
+	if (count + 1 > PAGE_SIZE)
+		count = PAGE_SIZE - 1;
+
 	/*
 	 * if no m/c have been assigned to this writer up to this
 	 * point, use "default" policy entry
-- 
2.19.1