Commit 6451245e authored by Willem de Bruijn's avatar Willem de Bruijn Committed by Ben Hutchings

tun: read vnet_hdr_sz once

[ Upstream commit e1edab87 ]

When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
Data length is verified to be greater than or equal to expected header
length tun->vnet_hdr_sz before copying.

Read this value once and cache locally, as it can be updated between
the test and use (TOCTOU).
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
CC: Eric Dumazet <edumazet@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
 - Use ACCESS_ONCE() instead of READ_ONCE()
 - Adjust context]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 12e8c6a7
...@@ -625,9 +625,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, ...@@ -625,9 +625,11 @@ static ssize_t tun_get_user(struct tun_struct *tun,
} }
if (tun->flags & TUN_VNET_HDR) { if (tun->flags & TUN_VNET_HDR) {
if (len < tun->vnet_hdr_sz) int vnet_hdr_sz = ACCESS_ONCE(tun->vnet_hdr_sz);
if (len < vnet_hdr_sz)
return -EINVAL; return -EINVAL;
len -= tun->vnet_hdr_sz; len -= vnet_hdr_sz;
if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso))) if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
return -EFAULT; return -EFAULT;
...@@ -638,7 +640,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, ...@@ -638,7 +640,7 @@ static ssize_t tun_get_user(struct tun_struct *tun,
if (gso.hdr_len > len) if (gso.hdr_len > len)
return -EINVAL; return -EINVAL;
offset += tun->vnet_hdr_sz; offset += vnet_hdr_sz;
} }
if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) { if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
...@@ -770,7 +772,7 @@ static ssize_t tun_put_user(struct tun_struct *tun, ...@@ -770,7 +772,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
int vnet_hdr_sz = 0; int vnet_hdr_sz = 0;
if (tun->flags & TUN_VNET_HDR) if (tun->flags & TUN_VNET_HDR)
vnet_hdr_sz = tun->vnet_hdr_sz; vnet_hdr_sz = ACCESS_ONCE(tun->vnet_hdr_sz);
if (!(tun->flags & TUN_NO_PI)) { if (!(tun->flags & TUN_NO_PI)) {
if ((len -= sizeof(pi)) < 0) if ((len -= sizeof(pi)) < 0)
......
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