exec: load_script: kill the onstack interp[BINPRM_BUF_SIZE] array

Patch series "exec: binfmt_misc: fix use-after-free, kill
iname[BINPRM_BUF_SIZE]".

It looks like this code was always wrong, then commit 948b701a607f
("binfmt_misc: add persistent opened binary handler for containers")
added more problems.

This patch (of 6):

load_script() can simply use i_name instead, it points into bprm->buf[]
and nobody can change this memory until we call prepare_binprm().

The only complication is that we need to also change the signature of
bprm_change_interp() but this change looks good too.

While at it, do whitespace/style cleanups.

NOTE: the real motivation for this change is that people want to
increase BINPRM_BUF_SIZE, we need to change load_misc_binary() too but
this looks more complicated because afaics it is very buggy.

Link: http://lkml.kernel.org/r/20170918163446.GA26793@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Travis Gummels <tgummels@redhat.com>
Cc: Ben Woodard <woodard@redhat.com>
Cc: Jim Foraker <foraker1@llnl.gov>
Cc: <tdhooge@llnl.gov>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index afdf4e3..7cde3f4 100644 (file)
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -19,7 +19,6 @@ static int load_script(struct linux_binprm *bprm)
        const char *i_arg, *i_name;
        char *cp;
        struct file *file;
-       char interp[BINPRM_BUF_SIZE];
        int retval;
 
        if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
@@ -55,7 +54,7 @@ static int load_script(struct linux_binprm *bprm)
                        break;
        }
        for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
-       if (*cp == '\0') 
+       if (*cp == '\0')
                return -ENOEXEC; /* No interpreter name found */
        i_name = cp;
        i_arg = NULL;
@@ -65,7 +64,6 @@ static int load_script(struct linux_binprm *bprm)
                *cp++ = '\0';
        if (*cp)
                i_arg = cp;
-       strcpy (interp, i_name);
        /*
         * OK, we've parsed out the interpreter name and
         * (optional) argument.
@@ -80,24 +78,27 @@ static int load_script(struct linux_binprm *bprm)
        if (retval)
                return retval;
        retval = copy_strings_kernel(1, &bprm->interp, bprm);
-       if (retval < 0) return retval; 
+       if (retval < 0)
+               return retval;
        bprm->argc++;
        if (i_arg) {
                retval = copy_strings_kernel(1, &i_arg, bprm);
-               if (retval < 0) return retval; 
+               if (retval < 0)
+                       return retval;
                bprm->argc++;
        }
        retval = copy_strings_kernel(1, &i_name, bprm);
-       if (retval) return retval; 
+       if (retval)
+               return retval;
        bprm->argc++;
-       retval = bprm_change_interp(interp, bprm);
+       retval = bprm_change_interp(i_name, bprm);
        if (retval < 0)
                return retval;
 
        /*
         * OK, now restart the process with the interpreter's dentry.
         */
-       file = open_exec(interp);
+       file = open_exec(i_name);
        if (IS_ERR(file))
                return PTR_ERR(file);
 

diff --git a/fs/exec.c b/fs/exec.c
index ac34d97..5470d3c 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1410,7 +1410,7 @@ static void free_bprm(struct linux_binprm *bprm)
        kfree(bprm);
 }
 
-int bprm_change_interp(char *interp, struct linux_binprm *bprm)
+int bprm_change_interp(const char *interp, struct linux_binprm *bprm)
 {
        /* If a binfmt changed the interp, free it first. */
        if (bprm->interp != bprm->filename)

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index fb44d61..18d05b5 100644 (file)
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -131,7 +131,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm,
                           int executable_stack);
 extern int transfer_args_to_stack(struct linux_binprm *bprm,
                                  unsigned long *sp_location);
-extern int bprm_change_interp(char *interp, struct linux_binprm *bprm);
+extern int bprm_change_interp(const char *interp, struct linux_binprm *bprm);
 extern int copy_strings_kernel(int argc, const char *const *argv,
                               struct linux_binprm *bprm);
 extern int prepare_bprm_creds(struct linux_binprm *bprm);