On Fri, Aug 21, 2020 at 02:28:04PM -0400, Jeff Layton wrote: > Once we allow encrypted filenames we'll end up with names that may have > illegal characters in them (embedded '\0' or '/'), or characters that > aren't printable. > > It'll be safer to use strings that are printable. It turns out that the > MDS doesn't really care about the length of filenames, so we can just > base64 encode and decode filenames before writing and reading them. > > Lift the base64 implementation that's in fscrypt into lib/. Make fscrypt > select it when it's enabled. > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > --- > fs/crypto/Kconfig | 1 + > fs/crypto/fname.c | 59 +---------------------------------- > include/linux/base64.h | 11 +++++++ > lib/Kconfig | 3 ++ > lib/Makefile | 1 + > lib/base64.c | 71 ++++++++++++++++++++++++++++++++++++++++++ > 6 files changed, 88 insertions(+), 58 deletions(-) > create mode 100644 include/linux/base64.h > create mode 100644 lib/base64.c You need to be careful here because there are many subtly different variants of base64. The Wikipedia article is a good reference for this: https://en.wikipedia.org/wiki/Base64 For example, most versions of base64 use [A-Za-z0-9+/]. However that's *not* what fs/crypto/fname.c uses, since it needs the encoded strings to be valid filenames, and '/' isn't a valid character in filenames. Therefore, fs/crypto/fname.c uses ',' instead of '/'. It happens that's probably what ceph needs too. However, other kernel developers who come across a very generic-sounding "lib/base64.c" might expect it to implement a more common version of base64. Also, some versions of base64 pad the encoded string with "=" whereas others don't. The fs/crypto/fname.c implementation doesn't use padding. So if you're going to make a generic base64 library, you at least need to be very clear about exactly what version of base64 is meant. (FWIW, the existing use of base64 in fs/crypto/fname.c isn't part of a stable API. So it can still be changed to something else, as long as the encoding doesn't use the '/' or '\0' characters.) - Eric
