CVE-2023-52582

In the Linux kernel, the following vulnerability has been resolved:

netfs: Only call foliostartfscache() one time for each folio

If a network filesystem using netfs implements a clamp_length() function, it can set subrequest lengths smaller than a page size.

When we loop through the folios in netfsrrequnlockfolios() to set any folios to be written back, we need to make sure we only call foliostart_fscache() once for each folio.

Otherwise, this simple testcase:

mount -o fsc,rsize=1024,wsize=1024 127.0.0.1:/export /mnt/nfs dd if=/dev/zero of=/mnt/nfs/file.bin bs=4096 count=1 1+0 records in 1+0 records out 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.0126359 s, 324 kB/s echo 3 > /proc/sys/vm/drop_caches cat /mnt/nfs/file.bin > /dev/null

will trigger an oops similar to the following:

page dumped because: VMBUGONFOLIO(foliotestprivate2(folio)) ------------[ cut here ]------------ kernel BUG at include/linux/netfs.h:44! ... CPU: 5 PID: 134 Comm: kworker/u16:5 Kdump: loaded Not tainted 6.4.0-rc5 ... RIP: 0010:netfsrrequnlockfolios+0x68e/0x730 [netfs] ... Call Trace: netfsrreqassess+0x497/0x660 [netfs] netfssubreqterminated+0x32b/0x610 [netfs] nfsnetfsreadcompletion+0x14e/0x1a0 [nfs] nfsreadcompletion+0x2f9/0x330 [nfs] rpcfreetask+0x72/0xa0 [sunrpc] rpcasyncrelease+0x46/0x70 [sunrpc] processonework+0x3bd/0x710 workerthread+0x89/0x610 kthread+0x181/0x1c0 retfrom_fork+0x29/0x50