On Wed, Oct 30, 2024 at 09:09:03AM +0100, Stefano Brivio wrote: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(a)redhat.com>Reviewed-by: David Gibson <david(a)gibson.dropbear.id.au>--- arch.c | 6 +++++- conf.c | 13 +++++++++---- pasta.c | 11 ++++++++--- tap.c | 5 +++-- util.c | 30 ++++++++++++++++++++++++++++++ util.h | 2 ++ 6 files changed, 57 insertions(+), 10 deletions(-) diff --git a/arch.c b/arch.c index 04bebfc..d1dfb73 100644 --- a/arch.c +++ b/arch.c @@ -19,6 +19,7 @@ #include <unistd.h> #include "log.h" +#include "util.h" /** * arch_avx2_exec() - Switch to AVX2 build if supported @@ -40,7 +41,10 @@ void arch_avx2_exec(char **argv) if (__builtin_cpu_supports("avx2")) { char new_path[PATH_MAX + sizeof(".avx2")]; - snprintf(new_path, PATH_MAX + sizeof(".avx2"), "%s.avx2", exe); + if (snprintf_check(new_path, PATH_MAX + sizeof(".avx2"), + "%s.avx2", exe)) + die_perror("Can't build AVX2 executable path"); + execve(new_path, argv, environ); warn_perror("Can't run AVX2 build, using non-AVX2 version"); } 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"); + } } } diff --git a/pasta.c b/pasta.c index 307fb4a..a117704 100644 --- a/pasta.c +++ b/pasta.c @@ -102,7 +102,9 @@ static int pasta_wait_for_ns(void *arg) int flags = O_RDONLY | O_CLOEXEC; char ns[PATH_MAX]; - snprintf(ns, PATH_MAX, "/proc/%i/ns/net", pasta_child_pid); + if (snprintf_check(ns, PATH_MAX, "/proc/%i/ns/net", pasta_child_pid)) + die_perror("Can't build netns path"); + do { while ((c->pasta_netns_fd = open(ns, flags)) < 0) { if (errno != ENOENT) @@ -239,8 +241,11 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid, c->quiet = 1; /* Configure user and group mappings */ - snprintf(uidmap, BUFSIZ, "0 %u 1", uid); - snprintf(gidmap, BUFSIZ, "0 %u 1", gid); + if (snprintf_check(uidmap, BUFSIZ, "0 %u 1", uid)) + die_perror("Can't build uidmap"); + + if (snprintf_check(gidmap, BUFSIZ, "0 %u 1", gid)) + die_perror("Can't build gidmap"); if (write_file("/proc/self/uid_map", uidmap) || write_file("/proc/self/setgroups", "deny") || diff --git a/tap.c b/tap.c index c53a39b..cfb82e9 100644 --- a/tap.c +++ b/tap.c @@ -1151,8 +1151,9 @@ int tap_sock_unix_open(char *sock_path) if (*sock_path) memcpy(path, sock_path, UNIX_PATH_MAX); - else - snprintf(path, UNIX_PATH_MAX - 1, UNIX_SOCK_PATH, i); + else if (snprintf_check(path, UNIX_PATH_MAX - 1, + UNIX_SOCK_PATH, i)) + die_perror("Can't build UNIX domain socket path"); ex = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0); if (ex < 0) diff --git a/util.c b/util.c index eba7d52..21ce0a8 100644 --- a/util.c +++ b/util.c @@ -749,3 +749,33 @@ void close_open_files(int argc, char **argv) if (rc) die_perror("Failed to close files leaked by parent"); } + +/** + * snprintf_check() - snprintf() wrapper, checking for truncation and errors + * @str: Output buffer + * @size: Maximum size to write to @str + * @format: Message + * + * Return: false on success, true on truncation or error, sets errno on failure + */ +bool snprintf_check(char *str, size_t size, const char *format, ...) +{ + va_list ap; + int rc; + + va_start(ap, format); + rc = vsnprintf(str, size, format, ap); + va_end(ap); + + if (rc < 0) { + errno = EIO; + return true; + } + + if ((size_t)rc >= size) { + errno = ENOBUFS; + return true; + } + + return false; +} diff --git a/util.h b/util.h index 2c1e08e..96f178c 100644 --- a/util.h +++ b/util.h @@ -11,6 +11,7 @@ #include <stdbool.h> #include <stddef.h> #include <stdint.h> +#include <stdio.h> #include <string.h> #include <signal.h> #include <arpa/inet.h> @@ -200,6 +201,7 @@ int write_file(const char *path, const char *buf); int write_all_buf(int fd, const void *buf, size_t len); int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip); void close_open_files(int argc, char **argv); +bool snprintf_check(char *str, size_t size, const char *format, ...); /** * af_name() - Return name of an address family-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson