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bpf: Fix stack-out-of-bounds write in devmap

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get_upper_ifindexes() iterates over all upper devices and writes their
indices into an array without checking bounds.

Also the callers assume that the max number of upper devices is
MAX_NEST_DEV and allocate excluded_devices[1+MAX_NEST_DEV] on the stack,
but that assumption is not correct and the number of upper devices could
be larger than MAX_NEST_DEV (e.g., many macvlans), causing a
stack-out-of-bounds write.

Add a max parameter to get_upper_ifindexes() to avoid the issue.
When there are too many upper devices, return -EOVERFLOW and abort the
redirect.

To reproduce, create more than MAX_NEST_DEV(8) macvlans on a device with
an XDP program attached using BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS.
Then send a packet to the device to trigger the XDP redirect path.

Reported-by: syzbot+10cc7f13760b31bd2e61@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/698c4ce3.050a0220.340abe.000b.GAE@google.com/T/
Fixes: aeea1b86f9 ("bpf, devmap: Exclude XDP broadcast to master device")
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Link: https://lore.kernel.org/r/20260225053506.4738-1-kohei@enjuk.jp
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kohei Enju 2026-02-25 05:34:44 +00:00 • committed by Alexei Starovoitov
parent ad6fface76
commit b7bf516c3e
1 changed files with 17 additions and 5 deletions
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22
kernel/bpf/devmap.c
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@ -588,18 +588,22 @@ static inline bool is_ifindex_excluded(int *excluded, int num_excluded, int ifin
}
/* Get ifindex of each upper device. 'indexes' must be able to hold at
* least MAX_NEST_DEV elements.
* Returns the number of ifindexes added.
* least 'max' elements.
* Returns the number of ifindexes added, or -EOVERFLOW if there are too
* many upper devices.
*/
static int get_upper_ifindexes(struct net_device *dev, int *indexes)
static int get_upper_ifindexes(struct net_device *dev, int *indexes, int max)
{
struct net_device *upper;
struct list_head *iter;
int n = 0;
netdev_for_each_upper_dev_rcu(dev, upper, iter) {
if (n >= max)
return -EOVERFLOW;
indexes[n++] = upper->ifindex;
}
return n;
}
@ -615,7 +619,11 @@ int dev_map_enqueue_multi(struct xdp_frame *xdpf, struct net_device *dev_rx,
int err;
if (exclude_ingress) {
num_excluded = get_upper_ifindexes(dev_rx, excluded_devices);
num_excluded = get_upper_ifindexes(dev_rx, excluded_devices,
ARRAY_SIZE(excluded_devices) - 1);
if (num_excluded < 0)
return num_excluded;
excluded_devices[num_excluded++] = dev_rx->ifindex;
}
@ -733,7 +741,11 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb,
int err;
if (exclude_ingress) {
num_excluded = get_upper_ifindexes(dev, excluded_devices);
num_excluded = get_upper_ifindexes(dev, excluded_devices,
ARRAY_SIZE(excluded_devices) - 1);
if (num_excluded < 0)
return num_excluded;
excluded_devices[num_excluded++] = dev->ifindex;
}