Commit 6d8cb045 authored Mar 08, 2018 by Quentin Monnet Committed by Daniel Borkmann Mar 09, 2018

bpf: comment why dots in filenames under BPF virtual FS are not allowed



When pinning a file under the BPF virtual file system (traditionally
/sys/fs/bpf), using a dot in the name of the location to pin at is not
allowed. For example, trying to pin at "/sys/fs/bpf/foo.bar" will be
rejected with -EPERM.

This check was introduced at the same time as the BPF file system
itself, with commit b2197755 ("bpf: add support for persistent
maps/progs"). At this time, it was checked in a function called
"bpf_dname_reserved()", which made clear that using a dot was reserved
for future extensions.

This function disappeared and the check was moved elsewhere with commit
0c93b7d8 ("bpf: reject invalid names right in ->lookup()"), and the
meaning of the dot ban was lost.

The present commit simply adds a comment in the source to explain to the
reader that the usage of dots is reserved for future usage.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent 75a141af

kernel/bpf/inode.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -178,6 +178,9 @@ static int bpf_mkmap(struct dentry dentry, umode_t mode, void arg)
		static struct dentry *
		bpf_lookup(struct inode dir, struct dentry dentry, unsigned flags)
		{
		/* Dots in names (e.g. "/sys/fs/bpf/foo.bar") are reserved for future
		* extensions.
		*/
		if (strchr(dentry->d_name.name, '.'))
		return ERR_PTR(-EPERM);

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