D3316.id7711.diff
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	Index: sys/fs/devfs/devfs_vnops.c
	===================================================================
	--- sys/fs/devfs/devfs_vnops.c
	+++ sys/fs/devfs/devfs_vnops.c
	@@ -1774,13 +1774,24 @@
	return (EACCES);

	/*
	- * Character devices always share mappings, so
	- * require a writable fd for writable mappings.
	+ * If we are sharing potential changes via MAP_SHARED and we
	+ * are trying to get write permission although we opened it
	+ * without asking for it, bail out.
	+ *
	+ * Note that most character devices always share mappings.
	+ * The one exception is that D_MMAP_ANON devices
	+ * (i.e. /dev/zero) permit private writable mappings.
	+ *
	+ * Rely on vm_mmap_cdev() to fail invalid MAP_PRIVATE requests
	+ * as well as updating maxprot to permit writing for
	+ * D_MMAP_ANON devices rather than doing that here.
	*/
	- if ((fp->f_flag & FWRITE) != 0)
	- maxprot \|= VM_PROT_WRITE;
	- else if ((prot & VM_PROT_WRITE) != 0)
	- return (EACCES);
	+ if ((flags & MAP_SHARED) != 0) {
	+ if ((fp->f_flag & FWRITE) != 0)
	+ maxprot \|= VM_PROT_WRITE;
	+ else if ((prot & VM_PROT_WRITE) != 0)
	+ return (EACCES);
	+ }
	maxprot &= cap_maxprot;

	fpop = td->td_fpop;