Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: svcrdma: Reject Write/Reply chunks with segcount 0 A peer can send a Write or Reply chunk whose segcount field is zero. xdr_check_write_chunk() only rejects segcount > rc_maxpages, so zero passes the range check, and xdr_inline_decode(stream, 0) returns the current (non-NULL) cursor without advancing. The function returns true and pcl_alloc_write() then links a struct svc_rdma_chunk with ch_segcount == 0 onto rc_write_pcl or rc_reply_pcl. An earlier patch in this series made pcl_for_each_segment() safe for ch_segcount == 0, so this no longer drives the memory walk it used to. Rejecting the malformed frame at the decode boundary is still worthwhile as defense in depth: it keeps degenerate zero-segment chunks off the parsed chunk lists entirely, so any future consumer that walks ch_segments directly cannot observe one, and it makes the zero-floor easy to backport to trees where the macro change is more intrusive. RFC 8166 has no meaning for a Write/Reply chunk that describes no remote buffer, so no legitimate client is affected. xdr_check_reply_chunk() funnels Reply chunks through xdr_check_write_chunk() and inherits the same rejection. pcl_alloc_write() also links each chunk onto the parsed chunk list before filling its segment array. If a future change weakens the segcount-0 rejection, an incomplete chunk is visible to consumers during the fill loop. Reorder so that list_add_tail() follows the segment fill loop, ensuring only fully-populated chunks appear on the list.

Affected versions

Linux: 78147ca8b4a9b6cf0e597ddd6bf17959e08376c2 through before fe533ae1bed2ef2b3d54ee7ab410da1874ed3d4f (git); 78147ca8b4a9b6cf0e597ddd6bf17959e08376c2 through before a798714b58041e88716db3bf8fb03ae13eecd54a (git); 78147ca8b4a9b6cf0e597ddd6bf17959e08376c2 through before 45dbdb2637b7fc5f1355b588780d2a7fb0516805 (git); 78147ca8b4a9b6cf0e597ddd6bf17959e08376c2 through before 9808eb7656666acc7291bae9ab6b987bd16e47e0 (git); 5.11 Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.