[PATCH 4.4 02/31] i2c: dev: zero out array used for i2c reads from userspace

From: Sasha Levin
Date: Tue Aug 24 2021 - 13:40:02 EST

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

commit 86ff25ed6cd8240d18df58930bd8848b19fce308 upstream.

If an i2c driver happens to not provide the full amount of data that a
user asks for, it is possible that some uninitialized data could be sent
to userspace. While all in-kernel drivers look to be safe, just be sure
by initializing the buffer to zero before it is passed to the i2c driver
so that any future drivers will not have this issue.

Also properly copy the amount of data recvieved to the userspace buffer,
as pointed out by Dan Carpenter.

Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/i2c/i2c-dev.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 7584f292e2fd..d0340b134e72 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -148,7 +148,7 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,
if (count > 8192)
count = 8192;

- tmp = kmalloc(count, GFP_KERNEL);
+ tmp = kzalloc(count, GFP_KERNEL);
if (tmp == NULL)
return -ENOMEM;

@@ -157,7 +157,8 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,

ret = i2c_master_recv(client, tmp, count);
if (ret >= 0)
- ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;
+ if (copy_to_user(buf, tmp, ret))
+ ret = -EFAULT;
return ret;