execve updates for v6.14-rc1

- exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
   (Tycho Andersen, Kees Cook)
 
 - binfmt_misc: Fix comment typos (Christophe JAILLET)
 
 - exec: move empty argv[0] warning closer to actual logic (Nir Lichtman)
 
 - exec: remove legacy custom binfmt modules autoloading (Nir Lichtman)
 
 - binfmt_flat: Fix integer overflow bug on 32 bit systems (Dan Carpenter)
 
 - exec: Make sure set_task_comm() always NUL-terminates
 
 - coredump: Do not lock when copying "comm"
 
 - MAINTAINERS: add auxvec.h and set myself as maintainer
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Merge tag 'execve-v6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull execve updates from Kees Cook:

 - fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case (Tycho
   Andersen, Kees Cook)

 - binfmt_misc: Fix comment typos (Christophe JAILLET)

 - move empty argv[0] warning closer to actual logic (Nir Lichtman)

 - remove legacy custom binfmt modules autoloading (Nir Lichtman)

 - Make sure set_task_comm() always NUL-terminates

 - binfmt_flat: Fix integer overflow bug on 32 bit systems (Dan
   Carpenter)

 - coredump: Do not lock when copying "comm"

 - MAINTAINERS: add auxvec.h and set myself as maintainer

* tag 'execve-v6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  binfmt_flat: Fix integer overflow bug on 32 bit systems
  selftests/exec: add a test for execveat()'s comm
  exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case
  exec: Make sure task->comm is always NUL-terminated
  exec: remove legacy custom binfmt modules autoloading
  exec: move warning of null argv to be next to the relevant code
  fs: binfmt: Fix a typo
  MAINTAINERS: exec: Mark Kees as maintainer
  MAINTAINERS: exec: Add auxvec.h UAPI
  coredump: Do not lock during 'comm' reporting

MAINTAINERS

@@ -8548,8 +8548,8 @@ F:	rust/kernel/net/phy.rs
 F:	rust/kernel/net/phy/reg.rs
 
 EXEC & BINFMT API, ELF
+M:	Kees Cook <kees@kernel.org>
 R:	Eric Biederman <ebiederm@xmission.com>
-R:	Kees Cook <kees@kernel.org>
 L:	linux-mm@kvack.org
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/execve
@@ -8561,6 +8561,7 @@ F:	fs/tests/binfmt_*_kunit.c
 F:	fs/tests/exec_kunit.c
 F:	include/linux/binfmts.h
 F:	include/linux/elf.h
+F:	include/uapi/linux/auxvec.h
 F:	include/uapi/linux/binfmts.h
 F:	include/uapi/linux/elf.h
 F:	tools/testing/selftests/exec/

fs/binfmt_flat.c

@@ -478,7 +478,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 	 * 28 bits (256 MB) is way more than reasonable in this case.
 	 * If some top bits are set we have probable binary corruption.
 	*/
-	if ((text_len | data_len | bss_len | stack_len | full_data) >> 28) {
+	if ((text_len | data_len | bss_len | stack_len | relocs | full_data) >> 28) {
 		pr_err("bad header\n");
 		ret = -ENOEXEC;
 		goto err;

fs/binfmt_misc.c

@@ -1001,7 +1001,7 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 		/*
 		 * If it turns out that most user namespaces actually want to
 		 * register their own binary type handler and therefore all
-		 * create their own separate binfm_misc mounts we should
+		 * create their own separate binfmt_misc mounts we should
 		 * consider turning this into a kmem cache.
 		 */
 		misc = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);

fs/exec.c

@@ -1194,16 +1194,16 @@ static int unshare_sighand(struct task_struct *me)
 }
 
 /*
- * These functions flushes out all traces of the currently running executable
- * so that a new one can be started
+ * This is unlocked -- the string will always be NUL-terminated, but
+ * may show overlapping contents if racing concurrent reads.
  */
-
 void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 {
-	task_lock(tsk);
+	size_t len = min(strlen(buf), sizeof(tsk->comm) - 1);
+
 	trace_task_rename(tsk, buf);
-	strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
-	task_unlock(tsk);
+	memcpy(tsk->comm, buf, len);
+	memset(&tsk->comm[len], 0, sizeof(tsk->comm) - len);
 	perf_event_comm(tsk, exec);
 }
 
@@ -1341,7 +1341,28 @@ int begin_new_exec(struct linux_binprm * bprm)
 		set_dumpable(current->mm, SUID_DUMP_USER);
 
 	perf_event_exec();
-	__set_task_comm(me, kbasename(bprm->filename), true);
+
+	/*
+	 * If the original filename was empty, alloc_bprm() made up a path
+	 * that will probably not be useful to admins running ps or similar.
+	 * Let's fix it up to be something reasonable.
+	 */
+	if (bprm->comm_from_dentry) {
+		/*
+		 * Hold RCU lock to keep the name from being freed behind our back.
+		 * Use acquire semantics to make sure the terminating NUL from
+		 * __d_alloc() is seen.
+		 *
+		 * Note, we're deliberately sloppy here. We don't need to care about
+		 * detecting a concurrent rename and just want a terminated name.
+		 */
+		rcu_read_lock();
+		__set_task_comm(me, smp_load_acquire(&bprm->file->f_path.dentry->d_name.name),
+				true);
+		rcu_read_unlock();
+	} else {
+		__set_task_comm(me, kbasename(bprm->filename), true);
+	}
 
 	/* An exec changes our domain. We are no longer part of the thread
 	   group */
@@ -1517,11 +1538,13 @@ static struct linux_binprm *alloc_bprm(int fd, struct filename *filename, int fl
 	if (fd == AT_FDCWD || filename->name[0] == '/') {
 		bprm->filename = filename->name;
 	} else {
-		if (filename->name[0] == '\0')
+		if (filename->name[0] == '\0') {
 			bprm->fdpath = kasprintf(GFP_KERNEL, "/dev/fd/%d", fd);
-		else
+			bprm->comm_from_dentry = 1;
+		} else {
 			bprm->fdpath = kasprintf(GFP_KERNEL, "/dev/fd/%d/%s",
 						  fd, filename->name);
+		}
 		if (!bprm->fdpath)
 			goto out_free;
 
@@ -1719,13 +1742,11 @@ int remove_arg_zero(struct linux_binprm *bprm)
 }
 EXPORT_SYMBOL(remove_arg_zero);
 
-#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
 /*
  * cycle the list of binary formats handler, until one recognizes the image
  */
 static int search_binary_handler(struct linux_binprm *bprm)
 {
-	bool need_retry = IS_ENABLED(CONFIG_MODULES);
 	struct linux_binfmt *fmt;
 	int retval;
 
@@ -1737,8 +1758,6 @@ static int search_binary_handler(struct linux_binprm *bprm)
 	if (retval)
 		return retval;
 
-	retval = -ENOENT;
- retry:
 	read_lock(&binfmt_lock);
 	list_for_each_entry(fmt, &formats, lh) {
 		if (!try_module_get(fmt->module))
@@ -1756,17 +1775,7 @@ static int search_binary_handler(struct linux_binprm *bprm)
 	}
 	read_unlock(&binfmt_lock);
 
-	if (need_retry) {
-		if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
-		    printable(bprm->buf[2]) && printable(bprm->buf[3]))
-			return retval;
-		if (request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2)) < 0)
-			return retval;
-		need_retry = false;
-		goto retry;
-	}
-
-	return retval;
+	return -ENOEXEC;
 }
 
 /* binfmt handlers will call back into begin_new_exec() on success. */
@@ -1904,9 +1913,6 @@ static int do_execveat_common(int fd, struct filename *filename,
 	}
 
 	retval = count(argv, MAX_ARG_STRINGS);
-	if (retval == 0)
-		pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n",
-			     current->comm, bprm->filename);
 	if (retval < 0)
 		goto out_free;
 	bprm->argc = retval;
@@ -1944,6 +1950,9 @@ static int do_execveat_common(int fd, struct filename *filename,
 		if (retval < 0)
 			goto out_free;
 		bprm->argc = 1;
+
+		pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n",
+			     current->comm, bprm->filename);
 	}
 
 	retval = bprm_execve(bprm);

include/linux/binfmts.h

@@ -42,7 +42,9 @@ struct linux_binprm {
 		 * Set when errors can no longer be returned to the
 		 * original userspace.
 		 */
-		point_of_no_return:1;
+		point_of_no_return:1,
+		/* Set when "comm" must come from the dentry. */
+		comm_from_dentry:1;
 	struct file *executable; /* Executable to pass to the interpreter */
 	struct file *interpreter;
 	struct file *file;

include/linux/coredump.h

@@ -52,8 +52,8 @@ extern void do_coredump(const kernel_siginfo_t *siginfo);
 #define __COREDUMP_PRINTK(Level, Format, ...) \
 	do {	\
 		char comm[TASK_COMM_LEN];	\
-	\
-		get_task_comm(comm, current);	\
+		/* This will always be NUL terminated. */ \
+		memcpy(comm, current->comm, sizeof(comm)); \
 		printk_ratelimited(Level "coredump: %d(%*pE): " Format "\n",	\
 			task_tgid_vnr(current), (int)strlen(comm), comm, ##__VA_ARGS__);	\
 	} while (0)	\

include/linux/sched.h

@@ -1944,11 +1944,10 @@ static inline void kick_process(struct task_struct *tsk) { }
 #endif
 
 extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
-
-static inline void set_task_comm(struct task_struct *tsk, const char *from)
-{
-	__set_task_comm(tsk, from, false);
-}
+#define set_task_comm(tsk, from) ({			\
+	BUILD_BUG_ON(sizeof(from) != TASK_COMM_LEN);	\
+	__set_task_comm(tsk, from, false);		\
+})
 
 /*
  * - Why not use task_lock()?

io_uring/io-wq.c

@@ -634,7 +634,7 @@ static int io_wq_worker(void *data)
 	struct io_wq_acct *acct = io_wq_get_acct(worker);
 	struct io_wq *wq = worker->wq;
 	bool exit_mask = false, last_timeout = false;
-	char buf[TASK_COMM_LEN];
+	char buf[TASK_COMM_LEN] = {};
 
 	set_mask_bits(&worker->flags, 0,
 		      BIT(IO_WORKER_F_UP) | BIT(IO_WORKER_F_RUNNING));

io_uring/sqpoll.c

@@ -264,7 +264,7 @@ static int io_sq_thread(void *data)
 	struct io_ring_ctx *ctx;
 	struct rusage start;
 	unsigned long timeout = 0;
-	char buf[TASK_COMM_LEN];
+	char buf[TASK_COMM_LEN] = {};
 	DEFINE_WAIT(wait);
 
 	/* offload context creation failed, just exit */

kernel/kthread.c

@@ -738,10 +738,11 @@ EXPORT_SYMBOL(kthread_stop_put);
 
 int kthreadd(void *unused)
 {
+	static const char comm[TASK_COMM_LEN] = "kthreadd";
 	struct task_struct *tsk = current;
 
 	/* Setup a clean context for our children to inherit. */
-	set_task_comm(tsk, "kthreadd");
+	set_task_comm(tsk, comm);
 	ignore_signals(tsk);
 	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
 	set_mems_allowed(node_states[N_MEMORY]);

tools/testing/selftests/exec/execveat.c

@@ -23,9 +23,11 @@
 
 #include "../kselftest.h"
 
-#define TESTS_EXPECTED 51
+#define TESTS_EXPECTED 54
 #define TEST_NAME_LEN (PATH_MAX * 4)
 
+#define CHECK_COMM "CHECK_COMM"
+
 static char longpath[2 * PATH_MAX] = "";
 static char *envp[] = { "IN_TEST=yes", NULL, NULL };
 static char *argv[] = { "execveat", "99", NULL };
@@ -237,6 +239,29 @@ static int check_execveat_pathmax(int root_dfd, const char *src, int is_script)
 	return fail;
 }
 
+static int check_execveat_comm(int fd, char *argv0, char *expected)
+{
+	char buf[128], *old_env, *old_argv0;
+	int ret;
+
+	snprintf(buf, sizeof(buf), CHECK_COMM "=%s", expected);
+
+	old_env = envp[1];
+	envp[1] = buf;
+
+	old_argv0 = argv[0];
+	argv[0] = argv0;
+
+	ksft_print_msg("Check execveat(AT_EMPTY_PATH)'s comm is %s\n",
+		       expected);
+	ret = check_execveat_invoked_rc(fd, "", AT_EMPTY_PATH, 0, 0);
+
+	envp[1] = old_env;
+	argv[0] = old_argv0;
+
+	return ret;
+}
+
 static int run_tests(void)
 {
 	int fail = 0;
@@ -389,6 +414,14 @@ static int run_tests(void)
 
 	fail += check_execveat_pathmax(root_dfd, "execveat", 0);
 	fail += check_execveat_pathmax(root_dfd, "script", 1);
+
+	/* /proc/pid/comm gives filename by default */
+	fail += check_execveat_comm(fd, "sentinel", "execveat");
+	/* /proc/pid/comm gives argv[0] when invoked via link */
+	fail += check_execveat_comm(fd_symlink, "sentinel", "execveat");
+	/* /proc/pid/comm gives filename if NULL is passed */
+	fail += check_execveat_comm(fd, NULL, "execveat");
+
 	return fail;
 }
 
@@ -415,9 +448,13 @@ int main(int argc, char **argv)
 	int ii;
 	int rc;
 	const char *verbose = getenv("VERBOSE");
+	const char *check_comm = getenv(CHECK_COMM);
 
-	if (argc >= 2) {
-		/* If we are invoked with an argument, don't run tests. */
+	if (argc >= 2 || check_comm) {
+		/*
+		 * If we are invoked with an argument, or no arguments but a
+		 * command to check, don't run tests.
+		 */
 		const char *in_test = getenv("IN_TEST");
 
 		if (verbose) {
@@ -426,6 +463,38 @@ int main(int argc, char **argv)
 				ksft_print_msg("\t[%d]='%s\n'", ii, argv[ii]);
 		}
 
+		/* If the tests wanted us to check the command, do so. */
+		if (check_comm) {
+			/* TASK_COMM_LEN == 16 */
+			char buf[32];
+			int fd, ret;
+
+			fd = open("/proc/self/comm", O_RDONLY);
+			if (fd < 0) {
+				ksft_perror("open() comm failed");
+				exit(1);
+			}
+
+			ret = read(fd, buf, sizeof(buf));
+			if (ret < 0) {
+				ksft_perror("read() comm failed");
+				close(fd);
+				exit(1);
+			}
+			close(fd);
+
+			// trim off the \n
+			buf[ret-1] = 0;
+
+			if (strcmp(buf, check_comm)) {
+				ksft_print_msg("bad comm, got: %s expected: %s\n",
+					       buf, check_comm);
+				exit(1);
+			}
+
+			exit(0);
+		}
+
 		/* Check expected environment transferred. */
 		if (!in_test || strcmp(in_test, "yes") != 0) {
 			ksft_print_msg("no IN_TEST=yes in env\n");