CVE-2026-72466

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

xprtrdma: Fix bcall rep leak and unbounded peek

rpcrdma_is_bcall() decodes a reply's first words to decide whether

the frame is a backchannel call. Two issues in that decode path

let a short or malformed reply leak the receive buffer and drain

the Receive queue.

First, the speculative peek

p = xdr_inline_decode(xdr, 0);

/* five p++ reads follow */

asks xdr_inline_decode() for zero bytes, which returns xdr->p

without consulting xdr->end. The five subsequent __be32 reads can

then walk up to 20 bytes past the wire payload into stale regbuf

contents and misclassify the reply as a backchannel call.

Second, after the post-peek

p = xdr_inline_decode(xdr, 3 * sizeof(*p));

if (unlikely(!p))

return true;

the short-header arm returns true without calling

rpcrdma_bc_receive_call(). The contract with the caller is that a

true return transfers ownership of rep to the backchannel path:

rpcrdma_reply_handler()

if (rpcrdma_is_bcall(r_xprt, rep))

return; /* bare return, skips out_post */

...

out_post:

rpcrdma_post_recvs(r_xprt, credits + ...);

Because rpcrdma_bc_receive_call() never ran, no one took rep, but

rpcrdma_reply_handler still bare-returns past rpcrdma_rep_put()

and rpcrdma_post_recvs(). The rep, with its persistently

DMA-mapped receive buffer, is orphaned on rb_all_reps and freed

only at transport teardown. This completion reposts nothing, so

its slot is reclaimed only when a later forward-channel reply

reaches out_post and rpcrdma_post_recvs() allocates a fresh rep to

backfill; absent that traffic the Receive queue drains and the

peer's Sends draw RNR NAKs.

Fix by consulting xdr->end after the zero-length peek so the five

__be32 reads cannot run unless 20 bytes of wire payload remain. A

byte-precise comparison against xdr->end is required because a

non-4-aligned receive rounds the stream's word count up past the

true payload. Also return false from the short-header arm so the

reply falls through the normal out_norqst cleanup chain

(rpcrdma_rep_put() plus rpcrdma_post_recvs()).