CVE-2026-72466
Description
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()).