Commit ccbb18b6 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

exec/binfmt_script: Don't modify bprm->buf and then return -ENOEXEC 

The return code -ENOEXEC serves to tell search_binary_handler that it
should continue searching for the binfmt to handle a given file.  This
makes return -ENOEXEC with a bprm->buf that is needed to continue the
search problematic.

The current binfmt_script manages to escape problems as it closes and
clears bprm->file before return -ENOEXEC with bprm->buf modified.
This prevents search_binary_handler from looping as it explicitly
handles a NULL bprm->file.

I plan on moving all of the bprm->file managment into fs/exec.c and out
of the binary handlers so this will become a problem.

Move closing bprm->file and the test for BINPRM_PATH_INACCESSIBLE
down below the last return of -ENOEXEC.

Introduce i_sep and i_end to track the end of the first argument and
the end of the parameters respectively.  Using those, constification
of all char * pointers, and the helpers next_terminator and
next_non_spacetab guarantee the parameter parsing will not modify
bprm->buf.

Only modify bprm->buf to terminate the strings i_arg and i_name with
'\0' for passing to copy_strings_kernel.

When replacing loops with next_non_spacetab and next_terminator care
has been take that the logic of the parsing code (short of replacing
characters by '\0') remains the same.

Link: https://lkml.kernel.org/r/874ksczru6.fsf_-_@x220.int.ebiederm.org


Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 8b72ca90

fs/binfmt_script.c

+38 −42
Original line number Diff line number Diff line
@@ -16,14 +16,14 @@ 
#include <linux/fs.h>



static inline bool spacetab(char c) { return c == ' ' || c == '\t'; }

static inline char *next_non_spacetab(char *first, const char *last)

static inline const char *next_non_spacetab(const char *first, const char *last)

{

	for (; first <= last; first++)

		if (!spacetab(*first))

			return first;

	return NULL;

}

static inline char *next_terminator(char *first, const char *last)

static inline const char *next_terminator(const char *first, const char *last)

{

	for (; first <= last; first++)

		if (spacetab(*first) || !*first)
@@ -33,8 +33,7 @@ static inline char *next_terminator(char *first, const char *last) 


static int load_script(struct linux_binprm *bprm)

{

	const char *i_arg, *i_name;

	char *cp, *buf_end;

	const char *i_name, *i_sep, *i_arg, *i_end, *buf_end;

	struct file *file;

	int retval;
@@ -42,20 +41,6 @@ static int load_script(struct linux_binprm *bprm) 
	if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))

		return -ENOEXEC;



	/*

	 * If the script filename will be inaccessible after exec, typically

	 * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give

	 * up now (on the assumption that the interpreter will want to load

	 * this file).

	 */

	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)

		return -ENOENT;



	/* Release since we are not mapping a binary into memory. */

	allow_write_access(bprm->file);

	fput(bprm->file);

	bprm->file = NULL;



	/*

	 * This section handles parsing the #! line into separate

	 * interpreter path and argument strings. We must be careful
@@ -71,39 +56,48 @@ static int load_script(struct linux_binprm *bprm) 
	 * parse them on its own.

	 */

	buf_end = bprm->buf + sizeof(bprm->buf) - 1;

	cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n');

	if (!cp) {

		cp = next_non_spacetab(bprm->buf + 2, buf_end);

		if (!cp)

	i_end = strnchr(bprm->buf, sizeof(bprm->buf), '\n');

	if (!i_end) {

		i_end = next_non_spacetab(bprm->buf + 2, buf_end);

		if (!i_end)

			return -ENOEXEC; /* Entire buf is spaces/tabs */

		/*

		 * If there is no later space/tab/NUL we must assume the

		 * interpreter path is truncated.

		 */

		if (!next_terminator(cp, buf_end))

		if (!next_terminator(i_end, buf_end))

			return -ENOEXEC;

		cp = buf_end;

		i_end = buf_end;

	}

	/* NUL-terminate the buffer and any trailing spaces/tabs. */

	*cp = '\0';

	while (cp > bprm->buf) {

		cp--;

		if ((*cp == ' ') || (*cp == '\t'))

			*cp = '\0';

		else

			break;

	}

	for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);

	if (*cp == '\0')

	/* Trim any trailing spaces/tabs from i_end */

	while (spacetab(i_end[-1]))

		i_end--;



	/* Skip over leading spaces/tabs */

	i_name = next_non_spacetab(bprm->buf+2, i_end);

	if (!i_name || (i_name == i_end))

		return -ENOEXEC; /* No interpreter name found */

	i_name = cp;



	/* Is there an optional argument? */

	i_arg = NULL;

	for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++)

		/* nothing */ ;

	while ((*cp == ' ') || (*cp == '\t'))

		*cp++ = '\0';

	if (*cp)

		i_arg = cp;

	i_sep = next_terminator(i_name, i_end);

	if (i_sep && (*i_sep != '\0'))

		i_arg = next_non_spacetab(i_sep, i_end);



	/*

	 * If the script filename will be inaccessible after exec, typically

	 * because it is a "/dev/fd/<fd>/.." path against an O_CLOEXEC fd, give

	 * up now (on the assumption that the interpreter will want to load

	 * this file).

	 */

	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)

		return -ENOENT;



	/* Release since we are not mapping a binary into memory. */

	allow_write_access(bprm->file);

	fput(bprm->file);

	bprm->file = NULL;



	/*

	 * OK, we've parsed out the interpreter name and

	 * (optional) argument.
@@ -121,7 +115,9 @@ static int load_script(struct linux_binprm *bprm) 
	if (retval < 0)

		return retval;

	bprm->argc++;

	*((char *)i_end) = '\0';

	if (i_arg) {

		*((char *)i_sep) = '\0';

		retval = copy_strings_kernel(1, &i_arg, bprm);

		if (retval < 0)

			return retval;

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