Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: nfsd: add missing read barrier to rpc_status_get dumpit seqcount retry The hand-rolled seqcount-like protocol in nfsd_nl_rpc_status_get_dumpit() is missing a read memory barrier (smp_rmb) before its second counter check. The standard kernel read_seqcount_retry() includes smp_rmb() to ensure that all data reads complete before the counter is re-checked. Without this barrier, on weakly-ordered architectures (ARM, POWER), the CPU may reorder field reads past the second counter check, making the retry logic ineffective: it could observe a consistent counter pair while reading fields that have been concurrently modified by the writer. Add smp_rmb() before the second counter check to order the field reads ahead of it, matching the barrier semantics of the standard seqcount read-side. The begin-side smp_load_acquire() already pairs with the smp_store_release() in nfsd_dispatch(); with the smp_rmb() now ordering the field reads, the retry check no longer needs acquire semantics and reads the counter with a plain READ_ONCE(), as read_seqcount_retry() does. [ cel: Use READ_ONCE instead of smp_load_acquire() ]

Affected versions

Linux: bd9d6a3efa9709e653aafbeb859289feccb8e70c through before f501f2f4ec1d2dfe39e21c98630314074a9b30b0 (git); bd9d6a3efa9709e653aafbeb859289feccb8e70c through before 1aea0482b98ecd7d0249204665f2ad4ad517f66b (git); bd9d6a3efa9709e653aafbeb859289feccb8e70c through before 9b5f6475006cd8e3b5b99b8eb3cd74dbb1ce9df8 (git); bd9d6a3efa9709e653aafbeb859289feccb8e70c through before a71f161a857117e8e0264deb7d14fff5c98adcf5 (git); 6.7 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.