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selftests/bpf: add test case for BPF LSM hook bpf_lsm_mmap_file

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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>
Link: https://lore.kernel.org/r/20251216133000.3690723-2-mattbobrowski@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Matt Bobrowski 2025-12-16 13:30:00 +00:00 committed by Alexei Starovoitov
parent 94e948b7e6
commit d2749ae85a
1 changed files with 30 additions and 1 deletions
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31
tools/testing/selftests/bpf/progs/verifier_lsm.c
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@ -1,7 +1,8 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_misc.h"
SEC("lsm/file_permission")
@ -159,4 +160,32 @@ __naked int disabled_hook_test3(void *ctx)
::: __clobber_all);
}
SEC("lsm/mmap_file")
__description("not null checking nullable pointer in bpf_lsm_mmap_file")
__failure __msg("R1 invalid mem access 'trusted_ptr_or_null_'")
int BPF_PROG(no_null_check, struct file *file)
{
struct inode *inode;
inode = file->f_inode;
__sink(inode);
return 0;
}
SEC("lsm/mmap_file")
__description("null checking nullable pointer in bpf_lsm_mmap_file")
__success
int BPF_PROG(null_check, struct file *file)
{
struct inode *inode;
if (file) {
inode = file->f_inode;
__sink(inode);
}
return 0;
}
char _license[] SEC("license") = "GPL";