[PATCH 1/3] binfmt_misc: only let punctuation delimit a register string

[Christian Brauner <brauner@kernel.org>]

Currently we accept arbitrary delimiters which really makes no sense and
from looking around it's an unused feature. Everytime we add a flag the
number of possible delimiter shrinks and it makes extensions much more
hazardous than they need to be. Stop it and only accept punctional as
delimiters.

This extends commit 8e85d50ba111 ("binfmt_misc: reject a flag character
as the field delimiter").

Letters, digits, whitespace, control characters, bytes above 0x7f and
the backslash now get -EINVAL. Everything deployed uses ':' anyway.

Suggested-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/binfmt_misc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index ddfd3aa57ac8..809c91d21b39 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -100,6 +100,13 @@ static const struct binfmt_misc_flag *misc_flag_by_char(const char c)
 	return NULL;
 }
 
+static bool misc_valid_delim(const char c)
+{
+	if (!isascii(c) || !ispunct(c))
+		return false;
+	return c != '\\';
+}
+
 struct binfmt_misc_entry {
 	struct hlist_node node;
 	unsigned long flags;		/* type, status, etc. */
@@ -872,10 +879,9 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer,
 
 	del = *p++;	/* delimiter */
 
-	pr_debug("register: delim: %#x {%c}\n", del, del);
+	pr_debug("register: delim: %#x\n", del);
 
-	/* A flag-char delimiter runs the flag scan off the buffer. */
-	if (misc_flag_by_char(del))
+	if (!misc_valid_delim(del))
 		return ERR_PTR(-EINVAL);
 
 	/* Pad the buffer with the delim to simplify parsing below. */

-- 
2.53.0