Re: [PATCH v9 1/6] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags
From: Jan Kara <hidden>
Date: 2017-10-12 13:51:27
Also in:
linux-fsdevel, linux-mm, linux-xfs, nvdimm
Hi,
quoted hunk ↗ jump to hunk
diff --git a/mm/mmap.c b/mm/mmap.c index 680506faceae..2649c00581a0 100644 --- a/mm/mmap.c +++ b/mm/mmap.c@@ -1389,6 +1389,18 @@ unsigned long do_mmap(struct file *file, unsigned long addr, struct inode *inode = file_inode(file); switch (flags & MAP_TYPE) { + case MAP_SHARED_VALIDATE: + if ((flags & ~LEGACY_MAP_MASK) == 0) { + /* + * If all legacy mmap flags, downgrade + * to MAP_SHARED, i.e. invoke ->mmap() + * instead of ->mmap_validate() + */ + flags &= ~MAP_TYPE; + flags |= MAP_SHARED; + } else if (!file->f_op->mmap_validate) + return -EOPNOTSUPP; + /* fall through */ case MAP_SHARED: if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE)) return -EACCES;
When thinking a bit more about this I've realized one problem: Currently user can call mmap() with MAP_SHARED type and MAP_SYNC or MAP_DIRECT flags and he will get the new semantics (if the kernel happens to support it). I think that is undesirable and we should force usage of MAP_SHARED_VALIDATE when you want to use flags outside of LEGACY_MAP_MASK. So I'd just mask off non-legacy flags for MAP_SHARED mappings (so they would be silently ignored as they used to be until now). Honza -- Jan Kara [off-list ref] SUSE Labs, CR