diff options
| -rw-r--r-- | internal/syscallcompat/sys_common.go | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/internal/syscallcompat/sys_common.go b/internal/syscallcompat/sys_common.go index 33ed807..3a0d5a1 100644 --- a/internal/syscallcompat/sys_common.go +++ b/internal/syscallcompat/sys_common.go @@ -1,6 +1,7 @@ package syscallcompat import ( + "bytes" "syscall" "golang.org/x/sys/unix" @@ -45,3 +46,69 @@ func Faccessat(dirfd int, path string, mode uint32) error { func Linkat(olddirfd int, oldpath string, newdirfd int, newpath string, flags int) (err error) { return unix.Linkat(olddirfd, oldpath, newdirfd, newpath, flags) } + +const XATTR_SIZE_MAX = 65536 + +// Make the buffer 1kB bigger so we can detect overflows +const XATTR_BUFSZ = XATTR_SIZE_MAX + 1024 + +// Fgetxattr is a wrapper around unix.Fgetxattr that handles the buffer sizing. +func Fgetxattr(fd int, attr string) (val []byte, err error) { + // If the buffer is too small to fit the value, Linux and MacOS react + // differently: + // Linux: returns an ERANGE error and "-1" bytes. + // MacOS: truncates the value and returns "size" bytes. + // + // We choose the simple approach of buffer that is bigger than the limit on + // Linux, and return an error for everything that is bigger (which can + // only happen on MacOS). + // + // See https://github.com/pkg/xattr for a smarter solution. + // TODO: be smarter? + buf := make([]byte, XATTR_BUFSZ) + sz, err := unix.Fgetxattr(fd, attr, buf) + if err == syscall.ERANGE { + // Do NOT return ERANGE - the user might retry ad inifinitum! + return nil, syscall.EOVERFLOW + } + if err != nil { + return nil, err + } + if sz >= XATTR_SIZE_MAX { + return nil, syscall.EOVERFLOW + } + // Copy only the actually used bytes to a new (smaller) buffer + // so "buf" never leaves the function and can be allocated on the stack. + val = make([]byte, sz) + copy(val, buf) + return val, nil +} + +// Flistxattr is a wrapper unix.Flistxattr that handles buffer sizing and +// parsing the returned blob to a string slice. +func Flistxattr(fd int) (attrs []string, err error) { + // See the buffer sizing comments in Fgetxattr. + // TODO: be smarter? + buf := make([]byte, XATTR_BUFSZ) + sz, err := unix.Flistxattr(fd, buf) + if err == syscall.ERANGE { + // Do NOT return ERANGE - the user might retry ad inifinitum! + return nil, syscall.EOVERFLOW + } + if err != nil { + return nil, err + } + if sz >= XATTR_SIZE_MAX { + return nil, syscall.EOVERFLOW + } + buf = buf[:sz] + parts := bytes.Split(buf, []byte{0}) + for _, part := range parts { + if len(part) == 0 { + // Last part is empty, ignore + continue + } + attrs = append(attrs, string(part)) + } + return attrs, nil +} |