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net/packet: check length in getsockopt() called with PACKET_HDRLEN

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In the case getsockopt() is called with PACKET_HDRLEN and optlen < 4
|val| remains uninitialized and the syscall may behave differently
depending on its value, and even copy garbage to userspace on certain
architectures. To fix this we now return -EINVAL if optlen is too small.

This bug has been detected with KMSAN.

Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Potapenko 2017-04-25 18:51:46 +02:00 committed by David S. Miller
parent 8048ced9be
commit fd2c83b357
1 changed files with 2 additions and 0 deletions
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2
net/packet/af_packet.c
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@ -3836,6 +3836,8 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
case PACKET_HDRLEN:
if (len > sizeof(int))
len = sizeof(int);
if (len < sizeof(int))
return -EINVAL;
if (copy_from_user(&val, optval, len))
return -EFAULT;
switch (val) {