SUNRPC: Fix a slow server-side memory leak with RPC-over-TCP

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: Fix a slow server-side memory leak with RPC-over-TCP Jan Schunk reports that his small NFS servers suffer from memory exhaustion after just a few days. A bisect shows that commit e18e157bb5c8 ("SUNRPC: Send RPC message on TCP with a single sock_sendmsg() call") is the first bad commit. That commit assumed that sock_sendmsg() releases all the pages in the underlying bio_vec array, but the reality is that it doesn't. svc_xprt_release() releases the rqst's response pages, but the record marker page fragment isn't one of those, so it is never released. This is a narrow fix that can be applied to stable kernels. A more extensive fix is in the works.

References

• https://git.kernel.org/stable/c/1ba1291172f935e6b6fe703161a948f3347400b8
• https://git.kernel.org/stable/c/a2ebedf7bcd17a1194a0a18122c885eb578ee882
• https://git.kernel.org/stable/c/05258a0a69b3c5d2c003f818702c0a52b6fea861