treewide: Comply with CERT C rule ERR33-C for snprintf()

clang-tidy, starting from LLVM version 16, up to at least LLVM version
19, now checks that we detect and handle errors for snprintf() as
requested by CERT C rule ERR33-C. These warnings were logged with LLVM
version 19.1.2 (at least Debian and Fedora match):

/home/sbrivio/passt/arch.c:43:3: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
   43 |                 snprintf(new_path, PATH_MAX + sizeof(".avx2"), "%s.avx2", exe);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/arch.c:43:3: note: cast the expression to void to silence this warning
/home/sbrivio/passt/conf.c:577:4: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
  577 |                         snprintf(netns, PATH_MAX, "/proc/%ld/ns/net", pidval);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/conf.c:577:4: note: cast the expression to void to silence this warning
/home/sbrivio/passt/conf.c:579:5: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
  579 |                                 snprintf(userns, PATH_MAX, "/proc/%ld/ns/user",
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  580 |                                          pidval);
      |                                          ~~~~~~~
/home/sbrivio/passt/conf.c:579:5: note: cast the expression to void to silence this warning
/home/sbrivio/passt/pasta.c:105:2: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
  105 |         snprintf(ns, PATH_MAX, "/proc/%i/ns/net", pasta_child_pid);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/pasta.c:105:2: note: cast the expression to void to silence this warning
/home/sbrivio/passt/pasta.c:242:2: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
  242 |         snprintf(uidmap, BUFSIZ, "0 %u 1", uid);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/pasta.c:242:2: note: cast the expression to void to silence this warning
/home/sbrivio/passt/pasta.c:243:2: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
  243 |         snprintf(gidmap, BUFSIZ, "0 %u 1", gid);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/pasta.c:243:2: note: cast the expression to void to silence this warning
/home/sbrivio/passt/tap.c:1155:4: error: the value returned by this function should not be disregarded; neglecting it may lead to errors [cert-err33-c,-warnings-as-errors]
 1155 |                         snprintf(path, UNIX_PATH_MAX - 1, UNIX_SOCK_PATH, i);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/sbrivio/passt/tap.c:1155:4: note: cast the expression to void to silence this warning

Don't silence the warnings as they might actually have some merit. Add
an snprintf_check() function, instead, checking that we're not
truncating messages while printing to buffers, and terminate if the
check fails.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 9 insertions, 4 deletions

diff --git a/conf.c b/conf.c
index b3b5342..fa5cec3 100644
--- a/conf.c
+++ b/conf.c
@@ -574,10 +574,15 @@ static void conf_pasta_ns(int *netns_only, char *userns, char *netns,
 			if (pidval < 0 || pidval > INT_MAX)
 				die("Invalid PID %s", argv[optind]);
 
-			snprintf(netns, PATH_MAX, "/proc/%ld/ns/net", pidval);
-			if (!*userns)
-				snprintf(userns, PATH_MAX, "/proc/%ld/ns/user",
-					 pidval);
+			if (snprintf_check(netns, PATH_MAX,
+					   "/proc/%ld/ns/net", pidval))
+				die_perror("Can't build netns path");
+
+			if (!*userns) {
+				if (snprintf_check(userns, PATH_MAX,
+						   "/proc/%ld/ns/user", pidval))
+					die_perror("Can't build userns path");
+			}
 		}
 	}