bpf: prevent NULL pointer dereference within bpf_lsm_mmap_file #10459
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Provide a strong override for BPF LSM hook mmap_file() (bpf_lsm_mmap_file()) such that __nullable suffix parameter semantics (PTR_MAYBE_NULL) can be enforced by the BPF verifier onto the supplied BPF LSM program context. By doing this we force BPF LSM programs attached to mmap_file() (bpf_lsm_mmap_file()) to fundamentally have to NULL check the supplied struct file pointer parameter before attempting to dereference it, and therefore alleviate the risk of running into trivial NULL pointer dereference bugs, such as those reported in [0]. [0] https://lore.kernel.org/bpf/[email protected]/ Reported-by: Kaiyan Mei <[email protected]> Reported-by: Yinhao Hu <[email protected]> Reviewed-by: Dongliang Mu <[email protected]> Closes: https://lore.kernel.org/bpf/[email protected]/ Signed-off-by: Matt Bobrowski <[email protected]>
Add a trivial test case asserting that the BPF verifier does enforce __nullable suffix parameter semantics onto the struct file pointer parameter of BPF LSM hook bpf_lsm_mmap_file(). Dereferences on this struct file pointer without performing a NULL check are not to be permitted by the BPF verifier as a direct dereference on it could very well lead to a NULL pointer dereference. Signed-off-by: Matt Bobrowski <[email protected]>
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