kernel/kmod.c: check for NULL in call_usermodehelper_exec()

If /proc/sys/kernel/core_pattern contains only "|", a NULL pointer
dereference happens upon core dump because argv_split("") returns
argv[0] == NULL.

This bug was once fixed by commit 264b83c07a84 ("usermodehelper: check
subprocess_info->path != NULL") but was by error reintroduced by commit
7f57cfa4e2aa ("usermodehelper: kill the sub_info->path[0] check").

This bug seems to exist since 2.6.19 (the version which core dump to
pipe was added).  Depending on kernel version and config, some side
effect might happen immediately after this oops (e.g.  kernel panic with
2.6.32-358.18.1.el6).

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/kmod.c b/kernel/kmod.c
index fb326365b69466158b03b726e53c4fe15448fa89..b086006c59e7c6957a51984a3ec101ea2db8525d 100644 (file)
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -571,6 +571,10 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
        DECLARE_COMPLETION_ONSTACK(done);
        int retval = 0;
 
+       if (!sub_info->path) {
+               call_usermodehelper_freeinfo(sub_info);
+               return -EINVAL;
+       }
        helper_lock();
        if (!khelper_wq || usermodehelper_disabled) {
                retval = -EBUSY;