Vulnerability CVE-2024-46857
Published: 2024-09-27

Description:
In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: Fix bridge mode operations when there are no VFs

Currently, trying to set the bridge mode attribute when numvfs=0 leads to a
crash:

bridge link set dev eth2 hwmode vepa

[ 168.967392] BUG: kernel NULL pointer dereference, address: 0000000000000030
[...]
[ 168.969989] RIP: 0010:mlx5_add_flow_rules+0x1f/0x300 [mlx5_core]
[...]
[ 168.976037] Call Trace:
[ 168.976188] <TASK>
[ 168.978620] _mlx5_eswitch_set_vepa_locked+0x113/0x230 [mlx5_core]
[ 168.979074] mlx5_eswitch_set_vepa+0x7f/0xa0 [mlx5_core]
[ 168.979471] rtnl_bridge_setlink+0xe9/0x1f0
[ 168.979714] rtnetlink_rcv_msg+0x159/0x400
[ 168.980451] netlink_rcv_skb+0x54/0x100
[ 168.980675] netlink_unicast+0x241/0x360
[ 168.980918] netlink_sendmsg+0x1f6/0x430
[ 168.981162] ____sys_sendmsg+0x3bb/0x3f0
[ 168.982155] ___sys_sendmsg+0x88/0xd0
[ 168.985036] __sys_sendmsg+0x59/0xa0
[ 168.985477] do_syscall_64+0x79/0x150
[ 168.987273] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 168.987773] RIP: 0033:0x7f8f7950f917

(esw->fdb_table.legacy.vepa_fdb is null)

The bridge mode is only relevant when there are multiple functions per
port. Therefore, prevent setting and getting this setting when there are no
VFs.

Note that after this change, there are no settings to change on the PF
interface using `bridge link` when there are no VFs, so the interface no
longer appears in the `bridge link` output.

 References:
https://git.kernel.org/stable/c/52c4beb79e095e0631b5cac46ed48a2aefe51985
https://git.kernel.org/stable/c/65feee671e37f3b6eda0b6af28f204b5bcf7fa50
https://git.kernel.org/stable/c/505ae01f75f839b54329164bbfecf24cc1361b31
https://git.kernel.org/stable/c/b1d305abef4640af1b4f1b4774d513cd81b10cfc
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