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drivers: net: prevent tun_build_skb() to exceed the packet size limit

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commit 59eeb232940515590de513b997539ef495faca9a upstream.

Using the syzkaller repro with reduced packet size it was discovered
that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(),
although pad may be incremented in tun_build_skb(). This may end up
with exceeding the PAGE_SIZE limit in tun_build_skb().

Jason Wang <jasowang@redhat.com> proposed to count XDP_PACKET_HEADROOM
always (e.g. without rcu_access_pointer(tun->xdp_prog)) in
tun_can_build_skb() since there's a window during which XDP program
might be attached between tun_can_build_skb() and tun_build_skb().

Fixes: 7df13219d7 ("tun: reserve extra headroom only when XDP is set")
Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a
Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
Link: https://lore.kernel.org/r/20230803185947.2379988-1-andrew.kanner@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andrew Kanner 2023-08-03 20:59:48 +02:00 committed by Greg Kroah-Hartman
parent 6d701c95ee
commit 13f7752f4a
1 changed files with 1 additions and 1 deletions
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drivers/net/tun.c
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@ -1604,7 +1604,7 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
if (zerocopy)
return false;
if (SKB_DATA_ALIGN(len + TUN_RX_PAD) +
if (SKB_DATA_ALIGN(len + TUN_RX_PAD + XDP_PACKET_HEADROOM) +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
return false;