emacs-27 b9ec611: Fix buffer overflow in xbm_scan (bug#47094)

[Eli Zaretskii]

branch: emacs-27
commit b9ec6111e294af747958c6f13150b8dc99dba6e2
Author: Alan Third <alan@idiocy.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix buffer overflow in xbm_scan (bug#47094)
    
    * src/image.c (xbm_scan): Ensure reading a string doesn't overflow the
    buffer.
    
    (cherry picked from commit ebc3b25409dd614c1814a0643960452683e37aa3)
---
 src/image.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/image.c b/src/image.c
index cd095e0..e3eae5c 100644
--- a/src/image.c
+++ b/src/image.c
@@ -3256,6 +3256,7 @@ static int
 xbm_scan (char **s, char *end, char *sval, int *ival)
 {
   unsigned char c UNINIT;
+  char *sval_end = sval + BUFSIZ;
 
  loop:
 
@@ -3315,7 +3316,7 @@ xbm_scan (char **s, char *end, char *sval, int *ival)
   else if (c_isalpha (c) || c == '_')
     {
       *sval++ = c;
-      while (*s < end
+      while (*s < end && sval < sval_end
             && (c = *(*s)++, (c_isalnum (c) || c == '_')))
        *sval++ = c;
       *sval = 0;