devices: fix out-of-bounds write in BPF_PROG_QUERY - #69
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bpfAttrQuery only described the query member of union bpf_attr up to
prog_cnt, and that size (32 bytes) is what is passed to bpf(2). Since
Linux 6.16 (kernel commit 120933984460, "bpf: Implement mprog API on top
of existing cgroup progs"), __cgroup_bpf_query copies query.revision
back to userspace unconditionally, without looking at the size we
passed. As revision sits at offset 56, the kernel writes 8 bytes past
the end of the struct on every BPF_PROG_QUERY.
Depending on how the compiler lays out the frame, those 8 bytes either
land on unused stack space, and nothing happens, or on live data. In
runc this showed up as corrupted defer records, crashing "runc restore"
in runtime.copystack, and as garbled strings.
Kernel commit 21c4b99b27f3 ("bpf: fix BPF_PROG_QUERY OOB write and cgroup
backward compat") added the missing size check, but we have to keep
working on kernels that lack it, so describe the query struct in full.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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@opencontainers/cgroups-maintainers I want to release v0.0.9 once this is in. For analysis and repro, see #64 (comment) |
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bpfAttrQuery only described the query member of union bpf_attr up to prog_cnt, and that size (32 bytes) is what is passed to bpf(2). Since Linux 6.16 (kernel commit 120933984460, "bpf: Implement mprog API on top of existing cgroup progs"), __cgroup_bpf_query copies query.revision back to userspace unconditionally, without looking at the size we passed. As revision sits at offset 56, the kernel writes 8 bytes past the end of the struct on every BPF_PROG_QUERY.
Depending on how the compiler lays out the frame, those 8 bytes either land on unused stack space, and nothing happens, or on live data. In runc this showed up as corrupted defer records, crashing "runc restore" in runtime.copystack, and as garbled strings.
Kernel commit 21c4b99b27f3 ("bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat") added the missing size check, but we have to keep working on kernels that lack it, so describe the query struct in full.