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kernel_copy: avoid panic on unexpected OS error

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According to documentation, the listed errnos should only occur
if the `copy_file_range` call cannot be made at all, so the
assert be correct.  However, since in practice file system
drivers (incl. FUSE etc.) can return any errno they want, we
should not panic here.

Fixes #91152
This commit is contained in:
Georg Brandl 2021-11-23 08:09:48 +01:00
parent 2e055d92e0
commit b490ccc227
1 changed files with 4 additions and 2 deletions
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6
library/std/src/sys/unix/kernel_copy.rs
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@ -576,7 +576,7 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
return match err.raw_os_error() {
// when file offset + max_length > u64::MAX
Some(EOVERFLOW) => CopyResult::Fallback(written),
Some(ENOSYS | EXDEV | EINVAL | EPERM | EOPNOTSUPP | EBADF) => {
Some(ENOSYS | EXDEV | EINVAL | EPERM | EOPNOTSUPP | EBADF) if written == 0 => {
// Try fallback io::copy if either:
// - Kernel version is < 4.5 (ENOSYS¹)
// - Files are mounted on different fs (EXDEV)
@ -584,12 +584,14 @@ pub(super) fn copy_regular_files(reader: RawFd, writer: RawFd, max_len: u64) ->
// - copy_file_range file is immutable or syscall is blocked by seccomp¹ (EPERM)
// - copy_file_range cannot be used with pipes or device nodes (EINVAL)
// - the writer fd was opened with O_APPEND (EBADF²)
// and no bytes were written successfully yet. (All these errnos should
// not be returned if something was already written, but they happen in
// the wild, see #91152.)
//
// ¹ these cases should be detected by the initial probe but we handle them here
// anyway in case syscall interception changes during runtime
// ² actually invalid file descriptors would cause this too, but in that case
// the fallback code path is expected to encounter the same error again
assert_eq!(written, 0);
CopyResult::Fallback(0)
}
_ => CopyResult::Error(err, written),