[PATCH] libceph: reject buckets with mismatched CRUSH ids

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.

Fixes: 66a0e2d579db ("crush: remove mutable part of CRUSH map")
Assisted-by: Codex:gpt-5
Signed-off-by: Jérémy Jean <[email protected]>
---
 net/ceph/osdmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index a4b0dd8672ec..9c89f6602dff 100644
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -517,6 +517,8 @@ static struct crush_map *crush_decode(void *pbyval, void *end)
 
 		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;
-- 
2.47.3