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gconvert: Error out if g_escape_uri_string() would overflow

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If the string to escape contains a very large number of unacceptable
characters (which would need escaping), the calculation of the length of
the escaped string could overflow, leading to a potential write off the
end of the newly allocated string.

In addition to that, the number of unacceptable characters was counted
in a signed integer, which would overflow to become negative, making it
easier for an attacker to craft an input string which would cause an
out-of-bounds write.

Fix that by validating the allocation length, and using an unsigned
integer to count the number of unacceptable characters.

Spotted by treeplus. Thanks to the Sovereign Tech Resilience programme
from the Sovereign Tech Agency. ID: #YWH-PGM9867-134

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Fixes: #3827
This commit is contained in:
Philip Withnall
2025-11-13 18:27:22 +00:00
parent 298fa45f90
commit f28340ee62
1 changed files with 25 additions and 11 deletions
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36
glib/gconvert.c
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@@ -1336,8 +1336,9 @@ static const gchar hex[] = "0123456789ABCDEF";
/* Note: This escape function works on file: URIs, but if you want to
* escape something else, please read RFC-2396 */
static gchar *
g_escape_uri_string (const gchar *string,
UnsafeCharacterSet mask)
g_escape_uri_string (const gchar *string,
UnsafeCharacterSet mask,
GError **error)
{
#define ACCEPTABLE(a) ((a)>=32 && (a)<128 && (acceptable[(a)-32] & use_mask))
@@ -1345,7 +1346,7 @@ g_escape_uri_string (const gchar *string,
gchar *q;
gchar *result;
int c;
gint unacceptable;
size_t unacceptable;
UnsafeCharacterSet use_mask;
g_return_val_if_fail (mask == UNSAFE_ALL
@@ -1362,7 +1363,14 @@ g_escape_uri_string (const gchar *string,
if (!ACCEPTABLE (c))
unacceptable++;
}
if (unacceptable >= (G_MAXSIZE - (p - string)) / 2)
{
g_set_error_literal (error, G_CONVERT_ERROR, G_CONVERT_ERROR_BAD_URI,
_("The URI is too long"));
return NULL;
}
result = g_malloc (p - string + unacceptable * 2 + 1);
use_mask = mask;
@@ -1387,12 +1395,13 @@ g_escape_uri_string (const gchar *string,
static gchar *
g_escape_file_uri (const gchar *hostname,
const gchar *pathname)
g_escape_file_uri (const gchar *hostname,
const gchar *pathname,
GError **error)
{
char *escaped_hostname = NULL;
char *escaped_path;
char *res;
char *escaped_path = NULL;
char *res = NULL;
#ifdef G_OS_WIN32
char *p, *backslash;
@@ -1413,10 +1422,14 @@ g_escape_file_uri (const gchar *hostname,
if (hostname && *hostname != '\0')
{
escaped_hostname = g_escape_uri_string (hostname, UNSAFE_HOST);
escaped_hostname = g_escape_uri_string (hostname, UNSAFE_HOST, error);
if (escaped_hostname == NULL)
goto out;
}
escaped_path = g_escape_uri_string (pathname, UNSAFE_PATH);
escaped_path = g_escape_uri_string (pathname, UNSAFE_PATH, error);
if (escaped_path == NULL)
goto out;
res = g_strconcat ("file://",
(escaped_hostname) ? escaped_hostname : "",
@@ -1424,6 +1437,7 @@ g_escape_file_uri (const gchar *hostname,
escaped_path,
NULL);
out:
#ifdef G_OS_WIN32
g_free ((char *) pathname);
#endif
@@ -1753,7 +1767,7 @@ g_filename_to_uri (const gchar *filename,
hostname = NULL;
#endif
escaped_uri = g_escape_file_uri (hostname, filename);
escaped_uri = g_escape_file_uri (hostname, filename, error);
return escaped_uri;
}