Repository navigation
Conversation
When use_pty is enabled (the default) and the command's stderr is redirected to a pipe, socket or FIFO while its stdout is still the user's terminal, a third party reading that stderr (e.g. the tee in "sudo strace cmd 2> >(tee log)") writes back to the terminal itself. Since the terminal was in raw mode, the newline-only output was rendered staircased. Statically preserving the terminal's output flags, as is done for a piped stdout (commit 78b7121), would fix this but regress full-screen commands, which run their pty raw and emit bare newlines that ONLCR would mangle. Instead, track the command's OPOST state via its pty and toggle the user terminal's output flags to match as output is relayed: ONLCR while the command is cooked, raw while it is not. This is gated on stderr being a pipe/socket/FIFO, reuses sudo_term_raw() (no ABI change) and caches the applied state. While a full-screen command holds its pty raw, stderr echoed to the terminal by an external reader is still staircased; a single line discipline cannot serve both sudo's relayed output and a raw stream sudo does not control. This is no worse than before. Fixes GitHub issue sudo-project#349
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Preserve the user terminal's output flags (
OPOST/ONLCR) when stderris redirected to a pipe, socket or FIFO, and keep them in sync with the
command's pty while it runs (
sync_user_oflag()). When the command'spty performs output post-processing, the user terminal keeps it too;
when the command switches its pty to raw mode (e.g. a full-screen
program), the user terminal follows and goes raw as well.
Normal sessions are unaffected: the sync only arms when stderr is
redirected away from the terminal, and it reuses the existing
sudo_term_raw()interface, so there is no library ABI change.Testing
With the fix installed:
now renders with every line aligned to the left margin instead of
staircased.
make checkpasses forlib/utilandsrc.Known limitation
While a command holds its own pty in raw mode (full-screen/ncurses
programs such as vim or top), stderr echoed back to the now-raw terminal
by an external reader can still staircase: a single line discipline
cannot serve both sudo's relayed cooked output and an uncontrolled raw
third-party stream. This is no worse than the current behaviour. For
that case
strace -o file, sudo I/O logging, orDefaults>root !use_ptyremain the appropriate workarounds.Fixes GitHub issue #349