[added to the 3.18 stable tree] efi: Fix out-of-bounds read in variable_matches()

Sasha Levin
2016-05-19T04:17:25Z

From: Laszlo Ersek <lersek@redhat.com>

This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit 630ba0cc7a6dbafbdee43795617c872b35cde1b4 ]

The variable_matches() function can currently read "var_name[len]", for
example when:

- var_name[0] == 'a',
- len == 1
- match_name points to the NUL-terminated string "ab".

This function is supposed to accept "var_name" inputs that are not
NUL-terminated (hence the "len" parameter"). Document the function, and
access "var_name[*match]" only if "*match" is smaller than "len".

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Matthew Garrett <mjg59@coreos.com>
Cc: Jason Andryuk <jandryuk@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: <stable@vger.kernel.org> # v3.10+
Link: http://thread.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/86906
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
drivers/firmware/efi/vars.c | 37 ++++++++++++++++++++++++++-----------
1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 7f2ea21..6f182fd 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -202,29 +202,44 @@ static const struct variable_validate variable_validate[] = {
{ NULL_GUID, "", NULL },
};

+/*
+ * Check if @var_name matches the pattern given in @match_name.
+ *
+ * @var_name: an array of @len non-NUL characters.
+ * @match_name: a NUL-terminated pattern string, optionally ending in "*". A
+ * final "*" character matches any trailing characters @var_name,
+ * including the case when there are none left in @var_name.
+ * @match: on output, the number of non-wildcard characters in @match_name
+ * that @var_name matches, regardless of the return value.
+ * @return: whether @var_name fully matches @match_name.
+ */
static bool
variable_matches(const char *var_name, size_t len, const char *match_name,
int *match)
{
for (*match = 0; ; (*match)++) {
char c = match_name[*match];
- char u = var_name[*match];

- /* Wildcard in the matching name means we've matched */
- if (c == '*')
+ switch (c) {
+ case '*':
+ /* Wildcard in @match_name means we've matched. */
return true;

- /* Case sensitive match */
- if (!c && *match == len)
- return true;
+ case '\0':
+ /* @match_name has ended. Has @var_name too? */
+ return (*match == len);

- if (c != u)
+ default:
+ /*
+ * We've reached a non-wildcard char in @match_name.
+ * Continue only if there's an identical character in
+ * @var_name.
+ */
+ if (*match < len && c == var_name[*match])
+ continue;
return false;
-
- if (!c)
- return true;
+ }
}
- return true;
}

bool
--
2.5.0