bpf: Enforce expected_attach_type for tailcall compatibility #6055
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Yinhao et al. recently reported: Our fuzzer tool discovered an uninitialized pointer issue in the bpf_prog_test_run_xdp() function within the Linux kernel's BPF subsystem. This leads to a NULL pointer dereference when a BPF program attempts to deference the txq member of struct xdp_buff object. The test initializes two programs of BPF_PROG_TYPE_XDP: progA acts as the entry point for bpf_prog_test_run_xdp() and its expected_attach_type can neither be of be BPF_XDP_DEVMAP nor BPF_XDP_CPUMAP. progA calls into a slot of a tailcall map it owns. progB's expected_attach_type must be BPF_XDP_DEVMAP to pass xdp_is_valid_access() validation. The program returns struct xdp_md's egress_ifindex, and the latter is only allowed to be accessed under mentioned expected_attach_type. progB is then inserted into the tailcall which progA calls. The underlying issue goes beyond XDP though. Another example are programs of type BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access() as well as sock_addr_func_proto() have different logic depending on the programs' expected_attach_type. Similarly, a program attached to BPF_CGROUP_INET4_GETPEERNAME should not be allowed doing a tailcall into a program which calls bpf_bind() out of BPF which is only enabled for BPF_CGROUP_INET4_CONNECT. In short, specifying expected_attach_type allows to open up additional functionality or restrictions beyond what the basic bpf_prog_type enables. The use of tailcalls must not violate these constraints. Fix it by enforcing expected_attach_type in __bpf_prog_map_compatible(). Fixes: 5e43f89 ("bpf: Check attach type at prog load time") Reported-by: Yinhao Hu <[email protected]> Reported-by: Kaiyan Mei <[email protected]> Reviewed-by: Dongliang Mu <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]>
Add a small test case which adds two programs - one calling the other through a tailcall - and check that BPF rejects them in case of different expected_attach_type values: # ./vmtest.sh -- ./test_progs -t xdp_devmap [...] #641/1 xdp_devmap_attach/Verifier check of DEVMAP programs:OK #641 xdp_devmap_attach:OK Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED Signed-off-by: Daniel Borkmann <[email protected]>
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Upstream branch: d43029f |
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1006589 expired. Closing PR. |
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Pull request for series with
subject: bpf: Enforce expected_attach_type for tailcall compatibility
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1006589