[glibc/release/2.36/master] sunrpc: Suppress GCC -Os warning on user2netname

[glibc/release/2.36/master] sunrpc: Suppress GCC -Os warning on user2netname

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=997d844a97b0478a3a7f9e7d7027c7431edbb51d

commit 997d844a97b0478a3a7f9e7d7027c7431edbb51d
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Wed Sep 21 10:51:07 2022 -0300

    sunrpc: Suppress GCC -Os warning on user2netname
    
    GCC with -Os warns that sprint might overflow:
    
      netname.c: In function ‘user2netname’:
      netname.c:51:28: error: ‘%s’ directive writing up to 255 bytes into a
      region of size between 239 and 249 [-Werror=format-overflow=]
         51 |   sprintf (netname, "%s.%d@%s", OPSYS, uid, dfltdom);
            |                            ^~               ~~~~~~~
      netname.c:51:3: note: ‘sprintf’ output between 8 and 273 bytes into a
      destination of size 256
         51 |   sprintf (netname, "%s.%d@%s", OPSYS, uid, dfltdom);
            |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      cc1: all warnings being treated as errors
    
    However the code does test prior the sprintf call that dfltdom plus
    the required extra space for OPSYS, uid, and extra character will not
    overflow and return 0 instead.
    
    Checked on x86_64-linux-gnu and i686-linux-gnu.
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>
    Tested-by: Carlos O'Donell <carlos@redhat.com>
    
    (cherry picked from commit 6128e82ebe973163d2dd614d31753c88c0c4d645)

Diff:
---
 sunrpc/netname.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sunrpc/netname.c b/sunrpc/netname.c
index bf7f0b81c4..c1d1c43e50 100644
--- a/sunrpc/netname.c
+++ b/sunrpc/netname.c
@@ -20,6 +20,7 @@
 #include <string.h>
 #include <rpc/rpc.h>
 #include <shlib-compat.h>
+#include <libc-diag.h>
 
 #include "nsswitch.h"
 
@@ -48,7 +49,12 @@ user2netname (char netname[MAXNETNAMELEN + 1], const uid_t uid,
   if ((strlen (dfltdom) + OPSYS_LEN + 3 + MAXIPRINT) > (size_t) MAXNETNAMELEN)
     return 0;
 
+  /* GCC with -Os warns that sprint might overflow while handling dfltdom,
+     however the above test does check if an overflow would happen.  */
+  DIAG_PUSH_NEEDS_COMMENT;
+  DIAG_IGNORE_Os_NEEDS_COMMENT (8, "-Wformat-overflow");
   sprintf (netname, "%s.%d@%s", OPSYS, uid, dfltdom);
+  DIAG_POP_NEEDS_COMMENT;
   i = strlen (netname);
   if (netname[i - 1] == '.')
     netname[i - 1] = '\0';