bpf: annotate file argument as __nullable in bpf_lsm_mmap_file #10530
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As reported in [0], anonymous memory mappings are not backed by a struct file instance. Consequently, the struct file pointer passed to the security_mmap_file() LSM hook is NULL in such cases. The BPF verifier is currently unaware of this, allowing BPF LSM programs to dereference this struct file pointer without needing to perform an explicit NULL check. This leads to potential NULL pointer dereference and a kernel crash. Add a strong override for bpf_lsm_mmap_file() which annotates the struct file pointer parameter with the __nullable suffix. This explicitly informs the BPF verifier that this pointer (PTR_MAYBE_NULL) can be NULL, forcing BPF LSM programs to perform a check on it before dereferencing it. [0] https://lore.kernel.org/bpf/5e460d3c.4c3e9.19adde547d8.Coremail.kaiyanm@hust.edu.cn/ Reported-by: Kaiyan Mei <M202472210@hust.edu.cn> Reported-by: Yinhao Hu <dddddd@hust.edu.cn> Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn> Closes: https://lore.kernel.org/bpf/5e460d3c.4c3e9.19adde547d8.Coremail.kaiyanm@hust.edu.cn/ Signed-off-by: Matt Bobrowski <mattbobrowski@google.com> Acked-by: Song Liu <song@kernel.org>
Add a trivial test case asserting that the BPF verifier enforces PTR_MAYBE_NULL semantics on the struct file pointer argument of BPF LSM hook bpf_lsm_mmap_file(). Dereferencing the struct file pointer passed into bpf_lsm_mmap_file() without explicitly performing a NULL check first should not be permitted by the BPF verifier as it can lead to NULL pointer dereferences and a kernel crash. Signed-off-by: Matt Bobrowski <mattbobrowski@google.com> Acked-by: Song Liu <song@kernel.org>
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Upstream branch: 21f43f4 |
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1033769 irrelevant now. Closing PR. |
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Pull request for series with
subject: bpf: annotate file argument as __nullable in bpf_lsm_mmap_file
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1033769