diff options
| -rw-r--r-- | internal/syscallcompat/sys_linux.go | 36 |
1 files changed, 34 insertions, 2 deletions
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go index 6b75957..5c180ec 100644 --- a/internal/syscallcompat/sys_linux.go +++ b/internal/syscallcompat/sys_linux.go @@ -2,6 +2,7 @@ package syscallcompat import ( + "fmt" "sync" "syscall" @@ -97,12 +98,43 @@ func Dup3(oldfd int, newfd int, flags int) (err error) { // Fchmodat syscall. func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) { - // Linux does not support passing flags to fchmodat! From the man page: + // Linux does not support passing flags to Fchmodat! From the man page: // AT_SYMLINK_NOFOLLOW ... This flag is not currently implemented. // Linux ignores any flags, but Go stdlib rejects them with EOPNOTSUPP starting // with Go 1.11. See https://github.com/golang/go/issues/20130 for more info. // TODO: Use fchmodat2 once available on Linux. - return syscall.Fchmodat(dirfd, path, mode, 0) + + // Why would we ever want to call this without AT_SYMLINK_NOFOLLOW? + if flags&unix.AT_SYMLINK_NOFOLLOW == 0 { + tlog.Warn.Printf("Fchmodat: adding missing AT_SYMLINK_NOFOLLOW flag") + } + + // Open handle to the filename (but without opening the actual file). + fd, err := syscall.Openat(dirfd, path, syscall.O_NOFOLLOW|O_PATH, 0) + if err != nil { + return err + } + defer syscall.Close(fd) + + // Now we can check the type without the risk of race-conditions. + var st syscall.Stat_t + err = syscall.Fstat(fd, &st) + if err != nil { + return err + } + + // Return syscall.ELOOP if path refers to a symlink. + var a fuse.Attr + a.FromStat(&st) + if a.IsSymlink() { + return syscall.ELOOP + } + + // Change mode of the actual file. Note that we can neither use + // Fchmodat (since fd is not necessarily a directory) nor Fchmod + // (since we are using O_PATH). + procPath := fmt.Sprintf("/proc/self/fd/%d", fd) + return syscall.Chmod(procPath, mode) } // Fchownat syscall. |