{"id":"CVE-2026-93228","state":"PUBLISHED","title":"svcrdma: Reject Write/Reply chunks with segcount 0","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsvcrdma: Reject Write/Reply chunks with segcount 0\n\nA peer can send a Write or Reply chunk whose segcount field is zero.\nxdr_check_write_chunk() only rejects segcount > rc_maxpages, so zero\npasses the range check, and xdr_inline_decode(stream, 0) returns the\ncurrent (non-NULL) cursor without advancing. The function returns\ntrue and pcl_alloc_write() then links a struct svc_rdma_chunk with\nch_segcount == 0 onto rc_write_pcl or rc_reply_pcl.\n\nAn earlier patch in this series made pcl_for_each_segment() safe for\nch_segcount == 0, so this no longer drives the memory walk it used\nto. Rejecting the malformed frame at the decode boundary is still\nworthwhile as defense in depth: it keeps degenerate zero-segment\nchunks off the parsed chunk lists entirely, so any future consumer\nthat walks ch_segments directly cannot observe one, and it makes the\nzero-floor easy to backport to trees where the macro change is more\nintrusive. RFC 8166 has no meaning for a Write/Reply chunk that\ndescribes no remote buffer, so no legitimate client is affected.\n\nxdr_check_reply_chunk() funnels Reply chunks through\nxdr_check_write_chunk() and inherits the same rejection.\n\npcl_alloc_write() also links each chunk onto the parsed chunk list\nbefore filling its segment array. If a future change weakens the\nsegcount-0 rejection, an incomplete chunk is visible to consumers\nduring the fill loop. Reorder so that list_add_tail() follows the\nsegment fill loop, ensuring only fully-populated chunks appear on\nthe list.","publishedAt":"2026-09-24T15:29:10.087Z","updatedAt":"2026-10-30T12:36:26.967Z","severity":{"score":9.1,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"ac730b8cbaeec6831116e1455d909ecbdcdcbd34","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"28c5a3a572f6cf81ac304459cfd515480995d62a","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"fe533ae1bed2ef2b3d54ee7ab410da1874ed3d4f","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"a798714b58041e88716db3bf8fb03ae13eecd54a","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"45dbdb2637b7fc5f1355b588780d2a7fb0516805","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"9808eb7656666acc7291bae9ab6b987bd16e47e0","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/xprtrdma/svc_rdma_pcl.c","net/sunrpc/xprtrdma/svc_rdma_recvfrom.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.11","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/xprtrdma/svc_rdma_pcl.c","net/sunrpc/xprtrdma/svc_rdma_recvfrom.c"]}],"references":["https://git.kernel.org/stable/c/ac730b8cbaeec6831116e1455d909ecbdcdcbd34","https://git.kernel.org/stable/c/28c5a3a572f6cf81ac304459cfd515480995d62a","https://git.kernel.org/stable/c/fe533ae1bed2ef2b3d54ee7ab410da1874ed3d4f","https://git.kernel.org/stable/c/a798714b58041e88716db3bf8fb03ae13eecd54a","https://git.kernel.org/stable/c/45dbdb2637b7fc5f1355b588780d2a7fb0516805","https://git.kernel.org/stable/c/9808eb7656666acc7291bae9ab6b987bd16e47e0"],"weaknesses":[],"ingestedAt":"2026-10-30T12:56:04.490Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/93xxx/CVE-2026-93228.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-93228","state":"PUBLISHED","datePublished":"2026-09-24T15:29:10.087Z","dateUpdated":"2026-10-30T12:36:26.967Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-17T16:02:15.094Z"},"containers":{"cna":{"title":"svcrdma: Reject Write/Reply chunks with segcount 0","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsvcrdma: Reject Write/Reply chunks with segcount 0\n\nA peer can send a Write or Reply chunk whose segcount field is zero.\nxdr_check_write_chunk() only rejects segcount > rc_maxpages, so zero\npasses the range check, and xdr_inline_decode(stream, 0) returns the\ncurrent (non-NULL) cursor without advancing. The function returns\ntrue and pcl_alloc_write() then links a struct svc_rdma_chunk with\nch_segcount == 0 onto rc_write_pcl or rc_reply_pcl.\n\nAn earlier patch in this series made pcl_for_each_segment() safe for\nch_segcount == 0, so this no longer drives the memory walk it used\nto. Rejecting the malformed frame at the decode boundary is still\nworthwhile as defense in depth: it keeps degenerate zero-segment\nchunks off the parsed chunk lists entirely, so any future consumer\nthat walks ch_segments directly cannot observe one, and it makes the\nzero-floor easy to backport to trees where the macro change is more\nintrusive. RFC 8166 has no meaning for a Write/Reply chunk that\ndescribes no remote buffer, so no legitimate client is affected.\n\nxdr_check_reply_chunk() funnels Reply chunks through\nxdr_check_write_chunk() and inherits the same rejection.\n\npcl_alloc_write() also links each chunk onto the parsed chunk list\nbefore filling its segment array. If a future change weakens the\nsegcount-0 rejection, an incomplete chunk is visible to consumers\nduring the fill loop. Reorder so that list_add_tail() follows the\nsegment fill loop, ensuring only fully-populated chunks appear on\nthe list."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"ac730b8cbaeec6831116e1455d909ecbdcdcbd34","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"28c5a3a572f6cf81ac304459cfd515480995d62a","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"fe533ae1bed2ef2b3d54ee7ab410da1874ed3d4f","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"a798714b58041e88716db3bf8fb03ae13eecd54a","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"45dbdb2637b7fc5f1355b588780d2a7fb0516805","versionType":"git"},{"version":"78147ca8b4a9b6cf0e597ddd6bf17959e08376c2","status":"affected","lessThan":"9808eb7656666acc7291bae9ab6b987bd16e47e0","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/xprtrdma/svc_rdma_pcl.c","net/sunrpc/xprtrdma/svc_rdma_recvfrom.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.11","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.11","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/xprtrdma/svc_rdma_pcl.c","net/sunrpc/xprtrdma/svc_rdma_recvfrom.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/ac730b8cbaeec6831116e1455d909ecbdcdcbd34"},{"url":"https://git.kernel.org/stable/c/28c5a3a572f6cf81ac304459cfd515480995d62a"},{"url":"https://git.kernel.org/stable/c/fe533ae1bed2ef2b3d54ee7ab410da1874ed3d4f"},{"url":"https://git.kernel.org/stable/c/a798714b58041e88716db3bf8fb03ae13eecd54a"},{"url":"https://git.kernel.org/stable/c/45dbdb2637b7fc5f1355b588780d2a7fb0516805"},{"url":"https://git.kernel.org/stable/c/9808eb7656666acc7291bae9ab6b987bd16e47e0"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","baseScore":9.1,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - A remote NFS/RDMA peer places a Write or Reply chunk with segcount 0 in the RPC-over-RDMA transport header; svc_rdma_recvfrom() → svc_rdma_xdr_decode_req() → xdr_check_write_list()/xdr_check_reply_chunk() → xdr_check_write_chunk() accepted that field over iWARP or routable RoCEv2.\nAC:L - The attacker sets RPCRDMA_CMP_F_SND_W_INV_OK in the RDMA-CM private connect blob (svc_rdma_parse_connect_private) and sends a Write/Reply chunk with segcount 0; xdr_check_write_chunk() only rejected segcount > rc_maxpages, xdr_inline_decode(0) returns the cursor, and pcl_alloc_write() links a ch_segcount==0 chunk with no race.\nPR:N - xdr_check_write_chunk() and pcl_alloc_write() run in svc_rdma_xdr_decode_req() from svc_rdma_recvfrom() while parsing the transport header, before svc_xprt_do_recv() calls svc_process()/svc_authenticate(); RDMA CM accept performs no NFS credential check.\nUI:N - The attacker only needs to connect to a listening NFS/RDMA service and send an RPC-over-RDMA Call whose Write list or Reply chunk has segcount 0; no victim mount, click, or other user action is required.\nS:U - pcl_alloc_write() installs the empty chunk on the host kernel rc_write_pcl/rc_reply_pcl, and the subsequent heap walk and general protection fault stay inside nfsd's RPC-over-RDMA server; this is not a VM, IOMMU, or sandbox escape.\nC:H - Accepting segcount 0 in xdr_check_write_chunk() lets pcl_alloc_write() put a ch_segcount==0 Write/Reply chunk on the parsed list; pcl_for_each_segment then uses &ch_segments[0u-1u] and walks adjacent kernel heap at sizeof(struct svc_rdma_segment) stride, an unbounded out-of-bounds read.\nI:N - svc_rdma_get_inv_rkey() only loads segment->rs_handle from the overrun pointer to choose an invalidate rkey; Write/Reply encode and RDMA Write paths index with segno < ch_segcount and skip or return -E2BIG on an empty chunk, so there is no out-of-bounds write or control-flow hijack.\nA:H - The underflowed pcl_for_each_segment walk of the empty Write/Reply chunk continues until it hits unmapped memory and raises a general protection fault, oopsing or panicking the kernel, and the peer can send another zero-segcount Call to repeat it."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:36:26.967Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}