Affected: Linux

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

netfs: Call `invalidate_cache` only if implemented

Many filesystems such as NFS and Ceph do not implement the `invalidate_cache` method. On those filesystems, if writing to the cache (`NETFS_WRITE_TO_CACHE`) fails for some reason, the kernel crashes like this:

BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0010) - not-present page PGD 0 P4D 0 Oops: Oops: 0010 [#1] SMP PTI CPU: 9 UID: 0 PID: 3380 Comm: kworker/u193:11 Not tainted 6.13.3-cm4all1-hp #437 Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/17/2018 Workqueue: events_unbound netfs_write_collection_worker RIP: 0010:0x0 Code: Unable to access opcode bytes at 0xffffffffffffffd6. RSP: 0018:ffff9b86e2ca7dc0 EFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 7fffffffffffffff RDX: 0000000000000001 RSI: ffff89259d576a18 RDI: ffff89259d576900 RBP: ffff89259d5769b0 R08: ffff9b86e2ca7d28 R09: 0000000000000002 R10: ffff89258ceaca80 R11: 0000000000000001 R12: 0000000000000020 R13: ffff893d158b9338 R14: ffff89259d576900 R15: ffff89259d5769b0 FS: 0000000000000000(0000) GS:ffff893c9fa40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 000000054442e003 CR4: 00000000001706f0 Call Trace: <TASK> ? __die+0x1f/0x60 ? page_fault_oops+0x15c/0x460 ? try_to_wake_up+…