5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jérémy Jean commit 3cde4a8302301679937474a5f7a851394cc1bd11 upstream. crush_decode() stores bucket data by array slot, and the mapper later derives the per-bucket workspace index from the decoded bucket id. A malformed map can therefore make one bucket reuse another bucket's workspace by encoding an id different from -1 - slot. For uniform buckets, the second replica selection expands the source bucket's permutation into that aliased workspace buffer. If the source bucket is larger than the aliased bucket, the write runs past the smaller permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN reports a slab OOB write of 4 bytes in bucket_perm_choose(). Reject buckets whose encoded id does not match their array slot. Valid CRUSH maps already use the canonical negative id corresponding to the bucket slot, so this restores the invariant expected by work->work[-1 - in->id] without changing valid map behavior. Cc: stable@vger.kernel.org Fixes: 66a0e2d579db ("crush: remove mutable part of CRUSH map") Assisted-by: Codex:gpt-5 Signed-off-by: Jérémy Jean Reviewed-by: Alex Markuze Signed-off-by: Ilya Dryomov Signed-off-by: Greg Kroah-Hartman --- net/ceph/osdmap.c | 2 ++ 1 file changed, 2 insertions(+) --- a/net/ceph/osdmap.c +++ b/net/ceph/osdmap.c @@ -503,6 +503,8 @@ static struct crush_map *crush_decode(vo ceph_decode_need(p, end, 4*sizeof(u32), bad); b->id = ceph_decode_32(p); + if (b->id != -1 - i) + goto bad; b->type = ceph_decode_16(p); if (b->type == 0) goto bad;