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Nick Craig-Wood
3739ad9c35
Dir.Create, Dir.Mkdir and Dir.Rename joined whatever name they were
given onto the directory's path. A name of "..", "." or one containing
a "/" isn't a child of the directory, and at the VFS root
path.Join("", "..") preserves the ".." so the new node's path pointed
outside the root. Backends which join the Fs root with the remote then
resolved it to a location above the directory the VFS was created on.
serve nfs was exploitable through this. The go-nfs library refuses a
name of exactly "." or ".." in MKDIR only, doesn't check the name in
CREATE, RENAME or SYMLINK, and never refuses a name containing a "/".
serve webdav was exploitable in the same way and has its own fix. The
other serve front-ends rely on their own or their protocol library's
path cleaning to keep such names out of the VFS.
Reject such names with EINVAL in the VFS itself, so that every
front-end and mount is protected regardless of what the layer above it
checks. This is the fix for serve nfs and defence in depth for the
others. The serve webdav check is kept as the front-end is the trust
boundary and gives the client a clear error. The source name of a
rename is only used to look the node up so it isn't checked.
VFS.Mkdir of the root, which previously went through Dir.Mkdir with an
empty name and added a nameless child node to the root, now makes the
root directory on the backend directly, still honouring --read-only.
serve webdav and serve ftp made directories through Dir.Mkdir rather
than VFS.Mkdir, so they are switched to VFS.Mkdir to keep "MKCOL /" and
"MKD /" working.