CVE-2026-98070net/rds: acquire RDS_IN_XMIT in rds_tcp_reset_callbacks()

Official description

In the Linux kernel, the following vulnerability has been resolved: net/rds: acquire RDS_IN_XMIT in rds_tcp_reset_callbacks() rds_tcp_reset_callbacks() quiesces the transmit path by setting the path state to RDS_CONN_RESETTING and then waiting for RDS_IN_XMIT to be sampled clear before swapping the underlying socket and calling rds_send_path_reset(). Sampling the bit clear is not the same as owning it: rds_send_xmit() can re-acquire RDS_IN_XMIT right after the wait_event() returns. Its state recheck after taking the lock is a store-buffering pattern (the resetter writes the state and reads the bit, the sender writes the bit and reads the state) and acquire_in_xmit() is only an acquire operation, so on weakly ordered architectures both sides can miss each other's write and the transmit path then runs concurrently with rds_send_path_reset() rewriting cp_xmit_* state - which is exactly what the comment above rds_send_path_reset() tells its callers to prevent. Take the lock instead, hold it across the socket swap and rds_send_path_reset(), and release it with a wake-up at the end. The lock-ordering constraint documented above the wait still holds: the lock is acquired before lock_sock(), so a sender inside tcp_sendmsg() can never be waited on while we hold the socket lock. Two details of the old code go away with the same change: - t_sock is now read only after the lock is acquired. The old code cached it before waiting; the teardown in rds_conn_shutdown() releases that socket and clears t_sock, so a pointer cached before the wait can be stale by the time the accept path resumes. Reading it under RDS_IN_XMIT is what makes the exclusion complete once the teardown owns the same lock, which the next patch arranges; until then the teardown still only samples the bit, and the two paths remain as exposed to each other as they are today. - The old !osock early path called rds_send_path_reset() with no serialization at all. It now runs under the lock like the normal path. The conditional RDS_CONN_RESETTING transition of the previous patch happens before the socket check either way: a path found without a socket is either still connecting (its reconnect worker blocked on t_conn_path_lock) and legitimately goes RESETTING -> UP on the new socket, or it has been torn down meanwhile and is dropped. The in-function comment describing the old wait-based quiesce is rewritten to describe the lock-based one, and the stale block comment above the function (which still described a return value and an incomplete list of t_sock writers) is refreshed to name all four writers - the connect, accept, teardown and swap paths - and what serializes each of them.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/670af4e4a4de5e6bb5daee3838485571a0caa5fa
• https://git.kernel.org/stable/c/830a2e21b200c6b6fdccc63dd3f23932bf7a894b
• https://git.kernel.org/stable/c/a05790cb4ff03f797d76906990b148d83f63e7a3
• https://git.kernel.org/stable/c/d184e6dd4b8f3c20c018595fd09795a66b46c8ef
• https://git.kernel.org/stable/c/d625112564c3e980e02504270222b49b82690cee
• https://git.kernel.org/stable/c/8e4c3b7844c906c7097b4cfedd9dd1f48c9a6a92
• https://git.kernel.org/stable/c/062d9e008c67289e8e1b221ecdd8f9d60566d012
• https://git.kernel.org/stable/c/02c5f9dc2efd823e061954d564ce00bacd1bebeb