[PATCH] proc: fix /proc/*/map_files lookup

[Alexey Dobriyan <adobriyan@gmail.com>]

Current code does:

	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)

However sscanf() is broken garbage.

It silently accepts whitespace between format specifiers
(did you know that?).

It silently accepts valid strings which result in integer overflow.

Do not use sscanf() for any even remotely reliable parsing code.

	OK
	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000'
	/lib/systemd/systemd

	broken
	# readlink '/proc/1/map_files/               55a23af39000-55a23b05b000'
	/lib/systemd/systemd

	broken
	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000    '
	/lib/systemd/systemd

	very broken
	# readlink '/proc/1/map_files/1000000000000000055a23af39000-55a23b05b000'
	/lib/systemd/systemd

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: stable@kernel.org
---

 fs/proc/base.c |   29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -100,6 +100,8 @@
 #include "internal.h"
 #include "fd.h"
 
+#include "../../lib/kstrtox.h"
+
 /* NOTE:
  *	Implementing inode permission operations in /proc is almost
  *	certainly an error.  Permission checks need to happen during
@@ -1907,8 +1909,33 @@ bool proc_fill_cache(struct file *file, struct dir_context *ctx,
 static int dname_to_vma_addr(struct dentry *dentry,
 			     unsigned long *start, unsigned long *end)
 {
-	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)
+	const char *str = dentry->d_name.name;
+	unsigned long long sval, eval;
+	unsigned int len;
+
+	len = _parse_integer(str, 16, &sval);
+	if (len & KSTRTOX_OVERFLOW)
+		return -EINVAL;
+	if (sval != (unsigned long)sval)
+		return -EINVAL;
+	str += len;
+
+	if (*str != '-')
 		return -EINVAL;
+	str++;
+
+	len = _parse_integer(str, 16, &eval);
+	if (len & KSTRTOX_OVERFLOW)
+		return -EINVAL;
+	if (eval != (unsigned long)eval)
+		return -EINVAL;
+	str += len;
+
+	if (*str != '\0')
+		return -EINVAL;
+
+	*start = sval;
+	*end = eval;
 
 	return 0;
 }