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Documentation/bpf: Add documentation for filesystem kfuncs
Add a brief introduction for file system kfuncs:
bpf_get_file_xattr()
bpf_get_fsverity_digest()
The documentation highlights the strategy to avoid recursions of these
kfuncs.
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-4-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
authored by
Song Liu
and committed by
Alexei Starovoitov
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Documentation/bpf/fs_kfuncs.rst
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Documentation/bpf/fs_kfuncs.rst
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.. SPDX-License-Identifier: GPL-2.0
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.. _fs_kfuncs-header-label:
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=====================
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BPF filesystem kfuncs
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=====================
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BPF LSM programs need to access filesystem data from LSM hooks. The following
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BPF kfuncs can be used to get these data.
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* ``bpf_get_file_xattr()``
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* ``bpf_get_fsverity_digest()``
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To avoid recursions, these kfuncs follow the following rules:
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1. These kfuncs are only permitted from BPF LSM function.
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2. These kfuncs should not call into other LSM hooks, i.e. security_*(). For
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example, ``bpf_get_file_xattr()`` does not use ``vfs_getxattr()``, because
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the latter calls LSM hook ``security_inode_getxattr``.