* Gate the sed commands that run a shell
GNU sed executes a shell through its `e` command, both as a standalone
command (`sed -n '1e CMD' file`) and as an `s///e` flag that runs the
pattern space. It goes through popen(), so it is a literal `sh -c`, but
the terminal scan only ever saw `sed` at command position and treated the
program text as an ordinary argument.
That left `sed -n '1e rm -f victim' /etc/hosts` running with no prompt in
auto mode, and `_find_blocked_commands` returning nothing for it, so the
hard blocklist that applies in every mode missed `rm` as well.
Screens the program the same way the awk arm does. `-e` values are joined
with newlines first, since that is how sed assembles them: `sed -e '1a\'
-e 'e CMD'` appends a literal line and runs nothing, so judging the pieces
separately would prompt on a benign script. The scan then steps over every
region where `e` is data rather than a command: address and substitution
regexes, replacements, `a/i/c` text, `r`/`w` filenames, `b`/`t` labels and
comments. That keeps the common idioms silent, including `:e;N;$!be` loop
labels, `s/e/E/g`, and `s/a/b/we out.txt` where the `e` belongs to the `w`
filename and sed does not execute.
The blocklist scan recurses into a literal `e` payload the same way it
already does for `bash -c`. A bare `e` or an `s///e` can only be prompted,
since what they run is the pattern space, which is input-file text that is
not knowable statically.
Verified against real GNU sed 4.9 rather than the manual: 80 commands run
for real with a marker payload, comparing what sed actually executed
against the classifier, with no mismatches in either direction.
* Close five ways a sed program hid its shell payload
Review found five shapes the first pass missed. All five execute on GNU
sed 4.9, checked by running them rather than reading the manual.
A payload line ending in a backslash continues onto the next line, so the
scan now ends an `e` at an unescaped newline and unescapes the text the way
sed's read_text does. That is what resolves `r''m` back to `rm` for the
blocklist.
A sed comment ends at a real newline, but the terminal scan had already
replaced every newline with `;`, including newlines inside quotes, so
`# comment` swallowed the rest of the program. The sed arm now also sees a
variant where only unquoted newlines become separators, built on a
character-by-character quote scanner rather than a regex: an apostrophe in
a double-quoted word mis-pairs under a regex and inverts the state, which
opened a bypass while this was being written.
Everything attached to `-i` is a backup suffix, so reading `-ifoo` as an
attached `-f` lost the real script. Replaced the shared short-flag helper
with sed's own option grammar, which also fixes `-l 5` and
`--line-length 5` eating the script as their operand.
A sed child of `find -exec` was never recorded, so the blocklist skipped
its payload.
Substituted text splices straight into the program, and an address is as
good a place as any to open `;e CMD`, so a command substitution anywhere
in the program is treated as unresolvable. Scoped to the program: a
substitution in a file operand still runs, a `$(` or backtick inside single
quotes is literal, and parameter and arithmetic expansion are untouched.
The cost is that a substitution used to build a program now asks.
Bounding the -exec walk keeps the blocklist linear; without it a repeated
`-exec sed` line went quadratic.
Verified against real GNU sed across 103 commands run for real, no
mismatch in either direction.
* Fail closed on padded sed lines, and stop gating sed --sandbox
Four more from review, each checked by running it rather than reading the
manual.
The cap that keeps the argument walk linear was itself the bypass: padding
a line with 128 valid options pushes the script past it, and an empty
program read as proof the command only edits text. The budget is now shared
across the sed words on a line, so a lone sed reads its whole argument list
while a line packed with sed words keeps the floor that holds the walk
linear, and overflow fails closed instead of falling through.
The substitution scan counted parentheses without consulting quote state,
so a quoted paren in the substitution body left the span unterminated and
the program never matched. It now balances through the same quote scanner
used elsewhere, since a substitution body reopens quoting.
A wrapper between -exec and its child hid the child from the blocklist.
Following the wrapper also fixes the neighbouring blocked-name check, which
missed find . -exec env rm the same way. The wrapper's own name is still
screened: -exec sudo rm reports both.
sed --sandbox and --posix refuse e outright and exit 1, so gating them was
prompting for something that cannot run. They are now inert, except after
--, where the flag is an input filename and the script still executes.
env -u still hides a child from the blocklist, on this path and at top
level. That is pre-existing and left alone here.
* Resolve the sed program through find, wrappers, globs and variables
Five more from review, each run against real sed rather than read off the
manual.
find's -exec ends at + or ;, but the sed argument walk ran past it into the
next predicate, where a following -exec grep -e safe was read as sed's own
-e and discarded the real script. Stopping at the terminator also removes a
false prompt, since -exec was being parsed as -e xec and inventing a payload.
Hopping a wrapper skipped its name but not an option that takes a separate
operand, so env -u FOO sed returned FOO as the child. The table this file
already keeps for wrapper options covers it, moved up so both layers share
it. That also settles the top level: env -u PATH rm -rf x now reports rm,
as do env --unset, stdbuf -o L and xargs -I {}. Two false positives go with
it, timeout -s KILL 5 rm blaming the signal name and env -u kill blaming a
variable name, while timeout -s KILL 5 kill -9 1 still reports kill.
A program held in a variable was invisible: the assignment regex stops its
value at whitespace, so a program containing a newline never entered the
map in any pass. Resolved at the token level instead, where the value is
already whole. Both the written and the resolved program are screened,
since either can hold the e.
A command-position glob that can resolve to sed is treated as sed. The
auto gate already asks about any unresolved command glob; this is for the
blocklist, which did not know the name.
Inside double quotes a backslash makes the next character literal, so
sed "s/\$(CC)/gcc/" runs no substitution and should never have asked. The
quote scanner now reports an escaped character under its own state.
Left open: on Windows the blocklist lexer keeps quoting in its tokens, so
a multiline program held in a variable resolves there but not to a name
the blocklist reads. The prompt still fires on every platform.
* Ask when the sed program is not a literal we can read
Two from review, and the second one changes the default rather than adding
another case.
sed --sandbox and --posix were being read as disabling e for the whole
invocation. They disable exactly the scripts written after them: sed
compiles each -e as that option is parsed, and the positional script only
after the option list, so sed -e '1e CMD' input --sandbox runs the payload
with no POSIXLY_CORRECT needed. Suppression is now positional. Reading
POSIXLY_CORRECT out of the command text was considered and dropped as
unsound, since export or an outer bash -c puts it somewhere the text does
not show.
A program built by a parameter transformation was invisible: only bare
$NAME and ${NAME} were resolved, so ${p#x } passed through untouched. Rather
than add operators one at a time, a program that still holds a live
expansion after resolution is treated as unreadable and asks. Unhandled
expansion forms are now safe by default instead of silent, which also
closes ${p%Z}, array elements, printf -v, read, and p=$(...) whose binding
shlex had been truncating to a bare $.
Arithmetic is collapsed rather than exempted. It can only ever evaluate to
an integer, so it cannot spell a sed command, but leaving it as written let
"$((c+1))e CMD" read as an append-text command that swallowed the payload.
The cost is that a double-quoted program holding an unassigned variable now
asks: sed "s/$OLD/$NEW/g" f. Measured at 24 of 169 realistic invocations,
all of that one shape. Exempting it would trade enumerating expansion
operators for enumerating assignment forms, and four of the bypasses above
sit outside the assignment pattern, so the blanket rule stays.
Left open: -f prog.sed is still unscreened, since the program is in a file.
* Decide where a sed scan stops by context, not by token text
Four from review, two of them exploiting fixes from earlier rounds.
Stopping the sed walk at a + or ; token read the text after shlex had
already removed its quoting, so a quoted file operand looked exactly like
a find terminator and the scan gave up before the -e that followed. sed
still compiles that -e, because getopt permutes. Termination is now decided
by token index: a separator counts only if it was unquoted, and + or ; only
while a find or fd exec action is open, which is the only place quoting
does not matter. The same shape works with & | ( ) and }, so all of them
are covered.
The assignment map kept the first binding for a name, but the shell uses
the most recent one before the command. Bindings are now ordered and only
those preceding a given sed are folded in, with a later one replacing an
earlier. A value that is not itself literal clears the name rather than
leaving the older literal standing, which would otherwise have dressed an
unread program up as a safe one.
Exhausting the wrapper budget under find -exec returned the same answer as
finding no child at all, so a long enough chain of wrappers hid whatever
followed. It now reports overflow and blocks the chain word. This was
hiding more than sed: the same shape hid a plain rm.
fd spells its exec flags -x, -X, --exec and --exec-batch, none of which
were routed into the nested scan. They are now, but only while a find or
fd word is in scope and no action is already open, so a -x that belongs to
a child command is left alone.
Prompt rate is unchanged at 45 of 169 realistic invocations; this round
adds no new prompts.
* Drop the words the shell removes before a command runs
Two from review, both verified to run for real.
A redirection is performed by the shell and never reaches the command, but
the words stayed in the token list and the first of them was taken for
sed's positional script, so the real one behind it was never read.
`sed </dev/null '1e touch MARKER' input` creates the file, and so do the
`>`, `2>`, `2>&1`, `&>`, `>|` and here-string spellings. Redirections are
now recognised as spans and skipped: the target may be glued on, be the
next word, or sit one further along when a punctuation character splits
the operator. A skip is honoured only where sed would take the word as an
argument, so a pending -e/-f/-l value is still read.
The same words also hid a command outright. `> out.txt rm -rf victim` and
`2>&1 rm -rf victim` both really delete, because the redirection target
was read as the command word and the rm behind it landed in argument
position, where the always-on blocklist does not look.
shlex emits a RUN of punctuation characters as one token, so bash's `|&`
matched no separator and a sed scan ran on into the NEXT command, taking
its `-e safe` for the real script and dropping the payload. Any token
built only from those characters now ends an invocation, and a quoted one
is excluded the same way a quoted `';'` already was.
The third item from that review, `-l N` eating the script as its length
operand, was already closed in 9a5cfddb.
Prompt rate is unchanged at 45 of 169 realistic invocations; this round
adds no new prompts.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Read a sed program from what the shell really hands it
Five from an independent review pass, each verified by executing it.
sed joins its -e and -f sources with newlines, but a source boundary also
closes a line continuation open across it. Reading every -e as one
uninterrupted text let an unreadable -f in the middle hide the piece
behind it: `sed -e '1a\' -f /dev/null -e 'e CMD' input` runs CMD while the
same line without the -f only appends text.
A program flag ahead of the positional script makes that word an input
file. One behind it does so only while getopt permutes, and
POSIXLY_CORRECT turns permutation off from outside the command text, so
the positional is now read as a script as well. The suppression that a
flag written first performs is unchanged.
xargs builds the argv of the command behind it, appending what it reads on
stdin and substituting it into an -I placeholder, so the program need not
be in the text at all. A sed whose program is empty or is only the
placeholder is failed closed. The ordinary idioms are untouched: their
program is present and the placeholder stands where the file goes.
Only a word that really changes shell state rebinds a program held in a
variable. An assignment-shaped argument, one inside a subshell and one
used as a command's environment prefix all leave the variable alone, and
recording them replaced a payload with a value bash never assigned. A
conditional assignment after && or || may or may not run, so it clears the
name rather than being guessed at.
Exec-flag forwarding now starts only at a command word. Any token spelled
fd or find used to turn it on, so a -x or -exec in the text after one was
read as an exec flag and its neighbour hard-blocked; `echo fd -x rm` and
`grep fd -x rm file` were refused outright. A command-position glob bash
resolves to find is still recognised.
Prompt rate is unchanged at 45 of 169 realistic invocations.
* Judge a sed program against what getopt and find really do
Seven from review, each verified by executing it.
A redirection is removed wherever it stands, including where an option
value goes, so `sed -n -e >out '1e CMD' input` takes the word behind it as
the script. The skip is now honoured ahead of a pending value rather than
after it. The target of a detached redirection may itself look like an
option or a quoted operator, and the shell hands it to open() either way,
so `sed > --sandbox '1e CMD' input` and its `> ';'` twin no longer leave
that word standing as a sed flag or script. Only a bare operator is
refused, which is a malformed line.
A program flag written behind the positional script and the positional
itself are ALTERNATIVES, since permutation decides which sed compiles and
nothing in the text settles it. They were joined into one program, where an
unterminated command in the one swallowed the other: `-e safe` is an `s`
with delimiter `a` and no closing one, and it ate the payload behind it.
Each source is now scanned on its own.
find closes its batched form at `{} +` only, so a `+` anywhere else is an
ordinary argument it hands the child. Stopping at one threw away the script
behind it. The `;` spellings need no such test: a quoted `';'` and an
escaped `\;` reach find as the same word and it stops at either, which the
`;` twin of that line confirms by not executing.
An `-f` naming a stream (`-`, /dev/stdin, /dev/fd/N) takes the script off
stdin, which the same command line may well supply through a heredoc. That
is ignorance rather than safety, so the sed fails closed. A named program
file is unreadable in a different way and is unchanged.
bash expands the program word before sed is started, so in a directory
holding a suitably named file `sed *` runs whatever that file contains.
A program word carrying an unexpanded glob now fails closed. Quoted
programs expand nothing and a glob among the file operands is not the
program, so ordinary work is untouched.
Prompt rate is unchanged at 45 of 169 realistic invocations.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Keep command position and quoting intact through the sed scan
Six from review, two of them regressions the previous commit introduced.
Scoping exec-flag forwarding to a command word lost that position at a
shell keyword and across a wrapper's own operands, so `if true; then find
. -exec rm ...` and the `env -u FOO find ...` and `timeout 5 find ...`
shapes stopped blocking rm entirely. Keywords now keep the position and
wrapper options and their operands are stepped over, the way the command
walk already does.
Reading any operator-shaped token as a separator did the opposite: a
QUOTED one is data the command receives, so `printf '%s' '|&' rm` and
`grep '|&' rm file` were refused although they run nothing. The walk now
applies the same quoted-index exclusion the layout pass does, which also
clears the older `printf '%s' ';' rm` false positive.
ANSI-C decoding flattened the word's whitespace, and a sed program ends
its comment at exactly the newline that flattening destroyed. The decoded
text is re-quoted instead, keeping the spaces and the `#` around it, with
the newline standing as a mark so it stays data for whatever command
receives it rather than a place a new one begins.
An assignment inside a function body has not run and may never run, so it
is no longer recorded as the current value; the name is cleared instead,
which is right whether or not the function is later called.
An `-f` taking a process substitution is a generated /dev/fd/N script, and
the lexer ends the invocation at the `(` before the operand is read at
all. A still-pending program operand now fails the sed closed.
Live expansions were compared against the raw command spelling while the
sed program carried the post-lex one, so an escaped expansion read as
already resolved. Both sides are keyed without their escaping, which can
only make a spelling match and so errs closed.
Prompt rate is unchanged at 45 of 169 realistic invocations.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Read the sed program from the word the shell actually passes
Six from review, four of them bypasses and two false alarms.
find rewrites `{}` with the pathname it found before the child ever starts,
so a sed whose whole program is that placeholder was never read. Nested
under xargs it really runs whatever a suitably named file contains. A `{}`
among the file operands, which is the ordinary idiom, is not the program
and is untouched.
A quoted redirection is a word the command receives rather than something
the shell performs, and it was being removed either way, so a `-f` script
file named `>prog` disappeared and took the `-e` behind it out of view.
Quoting is now read from the operator the token opens with, which leaves
`2>'/dev/null'` a redirection with a quoted target.
An apostrophe in an ANSI-C word sent it down the flattening path, which
destroys the newline a sed comment ends at. The apostrophe is re-quoted
the way a shell does it instead.
fd takes the command attached to its short exec option, and only the exact
`-x` and `-X` spellings opened an action, so `-xrm` reached neither layer.
Conversely nothing behind a bare `--` is an option at all, and reading one
there refused `fd -- -x rm`, which merely lists a file.
The set of live expansions covers the whole command, so matching a sed
program against it by text alone attributed an expansion another command
performs to a program that only spells the same thing. Which occurrence it
was decides it now, and single quoting keeps its meaning while double
quoting does not.
Prompt rate is unchanged at 45 of 169 realistic invocations.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Tighten the comments this PR added
Every comment kept says why a rule exists and, where the reason is a
real tool behaviour, names the one command that proves it. What went is
narration of the code, the history of how each fix evolved, and the same
mechanism re-explained at each site that uses it: it is stated once at
the definition now and referred to from there.
Docstrings on the private helpers give what they return and the one fact
that is not obvious; the worked examples they carried are in the tests,
which already run them. The longest block is 8 lines, from 19.
229 lines off the diff. No code changed.
---------
Co-authored-by: danielhanchen <unslothai@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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