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authorIlya Leoshkevich <iii@linux.ibm.com>2019-10-28 13:29:02 +0100
committerAlexei Starovoitov <ast@kernel.org>2019-10-30 12:49:13 -0700
commit7541c87c9b7a7e07c84481f37f2c19063b44469b (patch)
treea1f47ae889424c14ebb736a51a075ac3ac2dd017 /kernel
parent050668c10047802a2b62cbf8db834c2c84042b87 (diff)
bpf: Allow narrow loads of bpf_sysctl fields with offset > 0
"ctx:file_pos sysctl:read read ok narrow" works on s390 by accident: it reads the wrong byte, which happens to have the expected value of 0. Improve the test by seeking to the 4th byte and expecting 4 instead of 0. This makes the latent problem apparent: the test attempts to read the first byte of bpf_sysctl.file_pos, assuming this is the least-significant byte, which is not the case on big-endian machines: a non-zero offset is needed. The point of the test is to verify narrow loads, so we cannot cheat our way out by simply using BPF_W. The existence of the test means that such loads have to be supported, most likely because llvm can generate them. Fix the test by adding a big-endian variant, which uses an offset to access the least-significant byte of bpf_sysctl.file_pos. This reveals the final problem: verifier rejects accesses to bpf_sysctl fields with offset > 0. Such accesses are already allowed for a wide range of structs: __sk_buff, bpf_sock_addr and sk_msg_md to name a few. Extend this support to bpf_sysctl by using bpf_ctx_range instead of offsetof when matching field offsets. Fixes: 7b146cebe30c ("bpf: Sysctl hook") Fixes: e1550bfe0de4 ("bpf: Add file_pos field to bpf_sysctl ctx") Fixes: 9a1027e52535 ("selftests/bpf: Test file_pos field in bpf_sysctl ctx") Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrey Ignatov <rdna@fb.com> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/20191028122902.9763-1-iii@linux.ibm.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/cgroup.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index ddd8addcdb5c..a3eaf08e7dd3 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1311,12 +1311,12 @@ static bool sysctl_is_valid_access(int off, int size, enum bpf_access_type type,
return false;
switch (off) {
- case offsetof(struct bpf_sysctl, write):
+ case bpf_ctx_range(struct bpf_sysctl, write):
if (type != BPF_READ)
return false;
bpf_ctx_record_field_size(info, size_default);
return bpf_ctx_narrow_access_ok(off, size, size_default);
- case offsetof(struct bpf_sysctl, file_pos):
+ case bpf_ctx_range(struct bpf_sysctl, file_pos):
if (type == BPF_READ) {
bpf_ctx_record_field_size(info, size_default);
return bpf_ctx_narrow_access_ok(off, size, size_default);