[LTP] [PATCH] binfmt_misc02.sh: Fix interpreter with uutils/coreutils

[LTP] [PATCH] binfmt_misc02.sh: Fix interpreter with uutils/coreutils

[Kuan-Ying Lee via ltp]

The test registers the system 'cat' directly as a binfmt_misc
interpreter and expects executing the data files to echo their content
back.

This breaks on distributions shipping the Rust uutils/coreutils
implementation (e.g. Ubuntu "Resolute"), where 'cat' is a hardlink to a
single multi-call 'coreutils' binary:

  $ readlink -f /usr/bin/cat
  /usr/lib/cargo/bin/coreutils/cat
  $ cat --version
  cat (uutils coreutils) 0.8.0

Such a binary has to work out which applet to run, and uutils does so
from AT_EXECFN, i.e. the path the kernel actually exec'd, rather than
from argv[0]. binfmt_misc sets argv[0] to the interpreter, but AT_EXECFN
keeps naming the file passed to the original execve(), so the applet
name is derived from the data file rather than from 'cat'. Renaming the
very same data file to "cat.extension" makes it work, which confirms
where the applet name comes from.

Hence the exec fails (exit 1) and subtests 1-4 report:

  binfmt_misc02 1 TFAIL: Fail to recognise a binary type

Subtests 5-6 pass because they expect no recognition and never run the
interpreter.

Fix it by registering a small wrapper script as the interpreter. The
shell execs cat itself, so argv[0] and AT_EXECFN name cat again and the
right applet is picked.

The interpreter path ends up in the binfmt_misc registration string,
whose delimiter is ':', '.' or ',' depending on the subtest, so the
path must contain none of them. That rules out $TST_TMPDIR, which
carries a '.', hence create the wrapper in a directory of our own
under $TMPDIR.

Signed-off-by: Kuan-Ying Lee <kuan-ying.lee@canonical.com>
---
 .../kernel/fs/binfmt_misc/binfmt_misc02.sh    | 44 +++++++++++++++----
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/testcases/kernel/fs/binfmt_misc/binfmt_misc02.sh b/testcases/kernel/fs/binfmt_misc/binfmt_misc02.sh
index 37c9b9e0f4e2..0d71f6a30ce9 100755
--- a/testcases/kernel/fs/binfmt_misc/binfmt_misc02.sh
+++ b/testcases/kernel/fs/binfmt_misc/binfmt_misc02.sh
@@ -18,8 +18,10 @@
 # We use various delimiteris to register a new binary type.
 
 TST_CNT=6
+TST_SETUP=binfmt_misc02_setup
+TST_CLEANUP=binfmt_misc02_cleanup
 TST_TESTFUNC=do_test
-TST_NEEDS_CMDS="cat head"
+TST_NEEDS_CMDS="cat chmod head mktemp"
 
 
 recognised_unrecognised()
@@ -85,22 +87,46 @@ verify_binfmt_misc()
 	remove_binary_type "$mntpoint/$name"
 }
 
-do_test()
+binfmt_misc02_setup()
 {
-	local cat="$(command -v cat)"
+	# The interpreter path becomes a field of the registration string,
+	# which is written with ':', '.' and ',' as delimiters below, so it
+	# must not contain any of them.
+	case "$TMPDIR" in
+	*[:.,]*) tst_brk TCONF "TMPDIR '$TMPDIR' contains ':', '.' or ','";;
+	esac
+
+	binfmt_misc_setup
+
+	interp_dir=$(mktemp -d "$TMPDIR/ltp_binfmt_miscXXXXXX")
+	[ -d "$interp_dir" ] || tst_brk TBROK "Failed to create interpreter dir"
+
+	interp="$interp_dir/interp"
+	printf '#!/bin/sh\nexec %s "$1"\n' "$(command -v cat)" > "$interp" ||
+		tst_brk TBROK "Failed to write $interp"
+	ROD chmod +x "$interp"
+}
 
+binfmt_misc02_cleanup()
+{
+	[ -n "$interp_dir" ] && rm -rf "$interp_dir"
+	binfmt_misc_cleanup
+}
+
+do_test()
+{
 	case $1 in
-	1) verify_binfmt_misc ":textension:E::extension::$cat:" \
+	1) verify_binfmt_misc ":textension:E::extension::$interp:" \
 			      "$TST_DATAROOT/file.extension" "1";;
-	2) verify_binfmt_misc ":tmagic:M:1:This::$cat:" \
+	2) verify_binfmt_misc ":tmagic:M:1:This::$interp:" \
 			      "$TST_DATAROOT/file.magic" "1";;
-	3) verify_binfmt_misc ".textension.E..extension..$cat." \
+	3) verify_binfmt_misc ".textension.E..extension..$interp." \
 			      "$TST_DATAROOT/file.extension" "1";;
-	4) verify_binfmt_misc ",tmagic,M,1,This,,$cat," \
+	4) verify_binfmt_misc ",tmagic,M,1,This,,$interp," \
 			      "$TST_DATAROOT/file.magic" "1";;
-	5) verify_binfmt_misc ":textension:E::ltp::$cat:" \
+	5) verify_binfmt_misc ":textension:E::ltp::$interp:" \
 			      "$TST_DATAROOT/file.extension" "0";;
-	6) verify_binfmt_misc ":tmagic:M:0:This::$cat:" \
+	6) verify_binfmt_misc ":tmagic:M:0:This::$interp:" \
 			      "$TST_DATAROOT/file.magic" "0";;
 	esac
 }
-- 
2.43.0


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Re: [LTP] binfmt_misc02.sh: Fix interpreter with uutils/coreutils

[linuxtestproject.agent]

Hi Kuan-Ying,

On Wed, 21 Oct 2026, Kuan-Ying Lee wrote:
> binfmt_misc02.sh: Fix interpreter with uutils/coreutils

> +	interp_dir=$(mktemp -d "$TMPDIR/ltp_binfmt_miscXXXXXX")
> +	[ -d "$interp_dir" ] || tst_brk TBROK "Failed to create interpreter dir"

With TMPDIR on a noexec filesystem and the datafiles on an executable
filesystem, open_exec() rejects this new interpreter with EACCES, causing
subtests 1-4 to report TFAIL despite working binfmt_misc support. The
previous system-cat interpreter did not depend on TMPDIR being executable.
Detect a noexec TMPDIR during setup and report TCONF, or place the wrapper
on an executable filesystem.

> +	printf '#!/bin/sh\nexec %s "$1"\n' "$(command -v cat)" > "$interp" ||

The resolved cat pathname is inserted unquoted into shell source: with
cat in a PATH directory containing spaces, the generated exec command
splits the pathname and exits 127 instead of running cat. Generate a
literal exec cat "$1" command instead, letting the shell perform PATH
lookup without reparsing the resolved pathname.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Re: [LTP] binfmt_misc02.sh: Fix interpreter with uutils/coreutils

[linuxtestproject.agent]

Hi Kuan-Ying,

On 12 Oct 2026, Kuan-Ying Lee wrote:
> binfmt_misc02.sh: Fix interpreter with uutils/coreutils

> +	printf '#!/bin/sh\nexec %s "$1"\n' "$(command -v cat)" > "$interp" ||
> +		tst_brk TBROK "Failed to write $interp"

The resolved cat pathname is inserted into the wrapper without shell
quoting. With cat in a PATH directory containing a space, the wrapper
executes a truncated pathname and subtests 1-4 incorrectly fail.
Generate 'exec cat "$1"' instead, or shell-quote the resolved pathname.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] [PATCH] binfmt_misc02.sh: Fix interpreter with uutils/coreutils

[Cyril Hrubis]

Hi!
> The test registers the system 'cat' directly as a binfmt_misc
> interpreter and expects executing the data files to echo their content
> back.
> 
> This breaks on distributions shipping the Rust uutils/coreutils
> implementation (e.g. Ubuntu "Resolute"), where 'cat' is a hardlink to a
> single multi-call 'coreutils' binary:
> 
>   $ readlink -f /usr/bin/cat
>   /usr/lib/cargo/bin/coreutils/cat
>   $ cat --version
>   cat (uutils coreutils) 0.8.0

That does sound like a bug in rust coreutils to me.

-- 
Cyril Hrubis
chrubis@suse.cz

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