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>
(cherry picked from commit 4c1c7be95c345cf2ad537a0c48e9aeadc7304527)
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 8ecc5096c56bfc3c39b3998cb0c3ab3fc4c166bc..3da09a9b40f260cb6da0da531ae5be50bebd1b77 100644 (file)
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -560,6 +560,10 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
        BUG_ON(atomic_read(&sub_info->cred->usage) != 1);
        validate_creds(sub_info->cred);
 
+       if (!sub_info->path) {
+               call_usermodehelper_freeinfo(sub_info);
+               return -EINVAL;
+       }
        helper_lock();
        if (sub_info->path[0] == '\0')
                goto out;