linux-kernel - PROBLEM: fs: hugetlbfs: boot failure due to specs sentinel missing on linux-next

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Message-ID: <20190204135403.ttitgfy22cp7h2lh@fsr-ub1664-175>
Date:   Mon, 4 Feb 2019 13:54:04 +0000
From:   Abel Vesa <abel.vesa@....com>
To:     David Howells <dhowells@...hat.com>
CC:     "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: PROBLEM: fs: hugetlbfs: boot failure due to specs sentinel missing on
 linux-next

Hi David,

I found this this morning trying to boot up i.MX8MQ platform.
It's totally unrelated though.

Your commit:
2284cf59cbcec "hugetlbfs: Convert to fs_context"
doesn't put a sentinel at the end of hugetlb_param_specs.

Then, the your commit:
f512b838c1048 "vfs: Add configuration parser helpers"
adds the fs_validate_description where you check for sentinel
but since the hugetlb_param_specs doesn't have it it freezes
inside the following printf:

+                       /* Check that the type is in range */
+                       if (t == __fs_param_wasnt_defined ||
+                           t >= nr__fs_parameter_type) {
+                               pr_err("VALIDATE %s: PARAM[%s] Bad type %u\n",
+                                      name, param->name, t);
+                               good = false;
+                       } else if (t == fs_param_is_enum) {
+                               enums = true;
+                       }

IMHO, what happens here is the missing sentinel allows your checking
here to go out of bounds and then the param->name is whatever garbage
happens to be at the end of that array and that makes the printf to
freeze.

This isn't something I looked at really close, so I might be wrong.

I wasn't able to find the mail with the patch to reply to that
so I had to write this as a separate mail.