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fusefrontend: -allow_other: set file mode after chown in Mkdir(). 

Make sure that the directory belongs to the correct owner before users
can access it. For directories with SUID/SGID mode, there is a risk of
race-conditions when files are created before the correct owner is set.
They will then inherit the wrong user and/or group.

See https://github.com/rfjakob/gocryptfs/issues/327 for more details.
This commit is contained in:
Sebastian Lackner 2019-01-09 02:33:06 +01:00 committed by Jakob Unterwurzacher
parent aae45b4d77
commit fcaca5fc94
1 changed files with 29 additions and 11 deletions
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40
internal/fusefrontend/fs_dir.go
View File

@ -64,6 +64,12 @@ func (fs *FS) Mkdir(newPath string, mode uint32, context *fuse.Context) (code fu
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
// Don't set the full mode before we have set the correct owner.
// See Create FUSE call for more details.
origMode := mode
if fs.args.PreserveOwner {
mode = 0000
}
if fs.args.PlaintextNames {
err = syscallcompat.Mkdirat(dirfd, cName, mode)
if err != nil {
@ -74,14 +80,23 @@ func (fs *FS) Mkdir(newPath string, mode uint32, context *fuse.Context) (code fu
err = syscallcompat.Fchownat(dirfd, cName, int(context.Owner.Uid),
int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir: Fchownat failed: %v", err)
tlog.Warn.Printf("Mkdir %q: Fchownat %d:%d failed: %v", cName, context.Owner.Uid, context.Owner.Gid, err)
// In case of a failure, we don't want to proceed setting more
// permissive modes.
return fuse.ToStatus(err)
}
}
// Set mode
if origMode != mode {
err = syscallcompat.Fchmodat(dirfd, cName, origMode, unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir %q: Fchmodat %#o -> %#o failed: %v", cName, mode, origMode, err)
}
}
return fuse.OK
}
// We need write and execute permissions to create gocryptfs.diriv
origMode := mode
mode = mode | 0300
// Handle long file name
@ -104,24 +119,27 @@ func (fs *FS) Mkdir(newPath string, mode uint32, context *fuse.Context) (code fu
return fuse.ToStatus(err)
}
}
// Set permissions back to what the user wanted
if origMode != mode {
err = syscallcompat.Fchmodat(dirfd, cName, origMode, unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir: Fchmodat failed: %v", err)
}
}
// Set owner
if fs.args.PreserveOwner {
err = syscallcompat.Fchownat(dirfd, cName, int(context.Owner.Uid),
int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir: Fchownat 1 failed: %v", err)
tlog.Warn.Printf("Mkdir %q: Fchownat(1) %d:%d failed: %v", cName, context.Owner.Uid, context.Owner.Gid, err)
// In case of a failure, we don't want to proceed setting more
// permissive modes.
return fuse.ToStatus(err)
}
err = syscallcompat.Fchownat(dirfd, filepath.Join(cName, nametransform.DirIVFilename),
int(context.Owner.Uid), int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir: Fchownat 2 failed: %v", err)
tlog.Warn.Printf("Mkdir %q: Fchownat(2) %d:%d failed: %v", cName, context.Owner.Uid, context.Owner.Gid, err)
}
}
// Set mode
if origMode != mode {
err = syscallcompat.Fchmodat(dirfd, cName, origMode, unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mkdir %q: Fchmodat %#o -> %#o failed: %v", cName, mode, origMode, err)
}
}
return fuse.OK