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selftests/bpf: Fix lsm_bdev dev_t encoding mismatch

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progs/lsm_bdev.c keys its verity_devices hashmap with the raw kernel dev_t
read straight off bdev->bd_dev, i.e. MKDEV(major, minor) = (major << 20) |
minor. prog_tests/lsm_bdev.c instead builds its lookup key with dev_key =
(__u32)st.st_rdev from stat(2), but the stat(2) syscall fills st_rdev via
the kernel's new_encode_dev(), a different bit layout: (minor & 0xff) |
(major << 8) | ((minor & ~0xff) << 12).

For any device with a non-trivial major these two values differ, so the
lookup can never find what the BPF program stored, and test_lsm_bdev()
always fails with:

  test_lsm_bdev:FAIL:map lookup unexpected error: -2 (errno 2)

Reconstruct the raw kernel dev_t from the decoded major/minor instead of
casting st_rdev directly, restoring the layout the BPF program actually
reads.

Fixes: 96f4c251a0 ("selftests/bpf: add block device management selftests")
Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
Acked-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/bpf/20260720-selftests-bpf_fixes-v2-2-b450eda93dfe@suse.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Ricardo B. Marlière 2026-07-20 08:13:08 -03:00 committed by Kumar Kartikeya Dwivedi
parent 0b236ac75d
commit 71cf3f3275
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1 changed files with 2 additions and 1 deletions
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tools/testing/selftests/bpf/prog_tests/lsm_bdev.c
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@ -17,6 +17,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <sys/types.h>
#include <unistd.h>
#include "lsm_bdev.skel.h"
@ -172,7 +173,7 @@ void test_lsm_bdev(void)
if (!ASSERT_OK(stat(DM_DEV_PATH, &st), "stat dm dev"))
goto remove_dm;
dev_key = (__u32)st.st_rdev;
dev_key = (major(st.st_rdev) << 20) | minor(st.st_rdev);
/* Look up the device in the BPF map and verify. */
err = bpf_map__lookup_elem(skel->maps.verity_devices,