CVE-2026-52995

In the Linux kernel, the following vulnerability has been resolved:

net/rds: zero per-item info buffer before handing it to visitors

rds_for_each_conn_info() and rds_walk_conn_path_info() both hand a
caller-allocated on-stack u64 buffer to a per-connection visitor and
then copy the full item_len bytes back to user space via
rds_info_copy() regardless of how much of the buffer the visitor
actually wrote.

rds_ib_conn_info_visitor() and rds6_ib_conn_info_visitor() only
write a subset of their output struct when the underlying
rds_connection is not in state RDS_CONN_UP (src/dst addr, tos, sl
and the two GIDs via explicit memsets). Several u32 fields
(max_send_wr, max_recv_wr, max_send_sge, rdma_mr_max, rdma_mr_size,
cache_allocs) and the 2-byte alignment hole between sl and
cache_allocs remain as whatever stack contents preceded the visitor
call and are then memcpy_to_user()'d out to user space.

struct rds_info_rdma_connection and struct rds6_info_rdma_connection
are the only rds_info_* structs in include/uapi/linux/rds.h that are
not marked __attribute__((packed)), so they have a real alignment
hole. The other info visitors (rds_conn_info_visitor,
rds6_conn_info_visitor, rds_tcp_tc_info, ...) write all fields of
their packed output struct today and are not known to be vulnerable,
but a future visitor that adds a conditional write-path would have
the same bug.

Reproduction on a kernel built without CONFIG_INIT_STACK_ALL_ZERO=y:
a local unprivileged user opens AF_RDS, sets SO_RDS_TRANSPORT=IB,
binds to a local address on an RDMA-capable netdev (rxe soft-RoCE on
any netdev is sufficient), sendto()'s any peer on the same subnet
(fails cleanly but installs an rds_connection in the global hash in
RDS_CONN_CONNECTING), then calls getsockopt(SOL_RDS,
RDS_INFO_IB_CONNECTIONS). The returned 68-byte item contains 26
bytes of stack garbage including kernel text/data pointers:

    0..7   0a 63 00 01 0a 63 00 02     src=10.99.0.1 dst=10.99.0.2
    8..39  00 ...                      gids (memset-zeroed)
    40..47 e0 92 a3 81 ff ff ff ff     kernel pointer (max_send_wr)
    48..55 7f 37 b5 81 ff ff ff ff     kernel pointer (rdma_mr_max)
    56..59 01 00 08 00                 rdma_mr_size (garbage)
    60..61 00 00                       tos, sl
    62..63 00 00                       alignment padding
    64..67 18 00 00 00                 cache_allocs (garbage)

Fix by zeroing the per-item buffer in both rds_for_each_conn_info()
and rds_walk_conn_path_info() before invoking the visitor. This
covers the IPv4/IPv6 IB visitors and hardens all current and future
visitors against the same class of bug.

No functional change for visitors that fully populate their output.

Changes in v2:
- retarget at the net tree (subject prefix "[PATCH net v2]",
  net/rds: prefix in the title)
- pick up Reviewed-by tags from Sharath Srinivasan and
  Allison Henderson