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bpf: fix accessing bpf_sysctl.file_pos on s390

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"ctx:file_pos sysctl:read write ok" fails on s390 with "Read value  !=
nux". This is because verifier rewrites a complete 32-bit
bpf_sysctl.file_pos update to a partial update of the first 32 bits of
64-bit *bpf_sysctl_kern.ppos, which is not correct on big-endian
systems.

Fix by using an offset on big-endian systems.

Ditto for bpf_sysctl.file_pos reads. Currently the test does not detect
a problem there, since it expects to see 0, which it gets with high
probability in error cases, so change it to seek to offset 3 and expect
3 in bpf_sysctl.file_pos.

Fixes: e1550bfe0d ("bpf: Add file_pos field to bpf_sysctl ctx")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20190816105300.49035-1-iii@linux.ibm.com/
This commit is contained in:
Ilya Leoshkevich
2019-08-16 12:53:00 +02:00
committed by Daniel Borkmann
parent af58e7ee6a
commit d895a0f16f
4 changed files with 22 additions and 9 deletions
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9
tools/testing/selftests/bpf/test_sysctl.c
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@@ -32,6 +32,7 @@ struct sysctl_test {
enum bpf_attach_type attach_type;
const char *sysctl;
int open_flags;
int seek;
const char *newval;
const char *oldval;
enum {
@@ -140,7 +141,7 @@ static struct sysctl_test tests[] = {
/* If (file_pos == X) */
BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_1,
offsetof(struct bpf_sysctl, file_pos)),
BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 0, 2),
BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 3, 2),
/* return ALLOW; */
BPF_MOV64_IMM(BPF_REG_0, 1),
@@ -153,6 +154,7 @@ static struct sysctl_test tests[] = {
.attach_type = BPF_CGROUP_SYSCTL,
.sysctl = "kernel/ostype",
.open_flags = O_RDONLY,
.seek = 3,
.result = SUCCESS,
},
{
@@ -1481,6 +1483,11 @@ static int access_sysctl(const char *sysctl_path,
if (fd < 0)
return fd;
if (test->seek && lseek(fd, test->seek, SEEK_SET) == -1) {
log_err("lseek(%d) failed", test->seek);
goto err;
}
if (test->open_flags == O_RDONLY) {
char buf[128];