bpf: Fix use-after-free in offloaded map/prog info fill

Overview

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

bpf: Fix use-after-free in offloaded map/prog info fill

When querying info for an offloaded BPF map or program, bpf_map_offload_info_fill_ns() and bpf_prog_offload_info_fill_ns() obtain the network namespace with get_net(dev_net(offmap->netdev)). However, the associated netdev's netns may be racing with teardown during netns destruction. If the netns refcount has already reached 0, get_net() performs a refcount_t increment on 0, triggering:

refcount_t: addition on 0; use-after-free.

Although rtnl_lock and bpf_devs_lock ensure the netdev pointer remains valid, they cannot prevent the netns refcount from reaching zero.

Fix this by using maybe_get_net() instead of get_net(). maybe_get_net() uses refcount_inc_not_zero() and returns NULL if the refcount is already zero, which causes ns_get_path_cb() to fail and the caller to return -ENOENT -- the correct behavior when the netns is being destroyed.

Affected

• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < 43d6848a2a6c92ccfd614d9f0bb6fd85b95dfa9d
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < 642943ae5bdacabc8109dc4a5e0ebb4a6b99ef3e
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < fea55b034328feaafef75aee252f305e6f85a991
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < 5662dac41a3442aa378d7c405164903eb109fc05
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < 1a2dc103e16448d022a77ad5fc3234641436c4b7
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < 85dc711f742b192eb97c0e00b521312f5a7a415e
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < a51e7fbe94a87e236631a83973d4f558310b2cd2
• Linux >= 675fc275a3a2d905535207237402c6d8dcb5fa4b < a0c584fc18056709c8e047a82a6045d6c209f4ce
• Linux 4.16

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.