[Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls

[Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

When invoking qemu-bridge-helper in 'net_bridge_run_helper',
instead of using fixed sized buffers, use dynamically allocated
ones initialised and returned by g_strdup_printf().

If bridge name 'br_buf' is undefined, pass empty string ("") to
g_strdup_printf() in its place, to avoid printing "(null)" string.

Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 net/tap.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

Update v5: add commit message about conditional 'br_buf' argument
  -> https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg06397.html

diff --git a/net/tap.c b/net/tap.c
index e8aadd8d4b..fc38029f41 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -498,9 +498,9 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
     }
     if (pid == 0) {
         int open_max = sysconf(_SC_OPEN_MAX), i;
-        char fd_buf[6+10];
-        char br_buf[6+IFNAMSIZ] = {0};
-        char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
+        char *fd_buf = NULL;
+        char *br_buf = NULL;
+        char *helper_cmd = NULL;
 
         for (i = 3; i < open_max; i++) {
             if (i != sv[1]) {
@@ -508,17 +508,17 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
             }
         }
 
-        snprintf(fd_buf, sizeof(fd_buf), "%s%d", "--fd=", sv[1]);
+        fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);
 
         if (strrchr(helper, ' ') || strrchr(helper, '\t')) {
             /* assume helper is a command */
 
             if (strstr(helper, "--br=") == NULL) {
-                snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
+                br_buf = g_strdup_printf("%s%s", "--br=", bridge);
             }
 
-            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s",
-                     helper, "--use-vnet", fd_buf, br_buf);
+            helper_cmd = g_strdup_printf("%s %s %s %s", helper,
+                            "--use-vnet", fd_buf, br_buf ? br_buf : "");
 
             parg = args;
             *parg++ = (char *)"sh";
@@ -527,10 +527,11 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
             *parg++ = NULL;
 
             execv("/bin/sh", args);
+            g_free(helper_cmd);
         } else {
             /* assume helper is just the executable path name */
 
-            snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
+            br_buf = g_strdup_printf("%s%s", "--br=", bridge);
 
             parg = args;
             *parg++ = (char *)helper;
@@ -541,6 +542,8 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
 
             execv(helper, args);
         }
+        g_free(fd_buf);
+        g_free(br_buf);
         _exit(1);
 
     } else {
-- 
2.21.0

Re: [Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls

[no-reply]

Patchew URL: https://patchew.org/QEMU/20190731091933.17363-1-ppandit@redhat.com/



Hi,

This series seems to have some coding style problems. See output below for
more information:

Type: series
Subject: [Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls
Message-id: 20190731091933.17363-1-ppandit@redhat.com

=== TEST SCRIPT BEGIN ===
#!/bin/bash
git rev-parse base > /dev/null || exit 0
git config --local diff.renamelimit 0
git config --local diff.renames True
git config --local diff.algorithm histogram
./scripts/checkpatch.pl --mailback base..
=== TEST SCRIPT END ===

Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
From https://github.com/patchew-project/qemu
 * [new tag]         patchew/20190731091933.17363-1-ppandit@redhat.com -> patchew/20190731091933.17363-1-ppandit@redhat.com
Submodule 'capstone' (https://git.qemu.org/git/capstone.git) registered for path 'capstone'
Submodule 'dtc' (https://git.qemu.org/git/dtc.git) registered for path 'dtc'
Submodule 'roms/QemuMacDrivers' (https://git.qemu.org/git/QemuMacDrivers.git) registered for path 'roms/QemuMacDrivers'
Submodule 'roms/SLOF' (https://git.qemu.org/git/SLOF.git) registered for path 'roms/SLOF'
Submodule 'roms/edk2' (https://git.qemu.org/git/edk2.git) registered for path 'roms/edk2'
Submodule 'roms/ipxe' (https://git.qemu.org/git/ipxe.git) registered for path 'roms/ipxe'
Submodule 'roms/openbios' (https://git.qemu.org/git/openbios.git) registered for path 'roms/openbios'
Submodule 'roms/openhackware' (https://git.qemu.org/git/openhackware.git) registered for path 'roms/openhackware'
Submodule 'roms/opensbi' (https://git.qemu.org/git/opensbi.git) registered for path 'roms/opensbi'
Submodule 'roms/qemu-palcode' (https://git.qemu.org/git/qemu-palcode.git) registered for path 'roms/qemu-palcode'
Submodule 'roms/seabios' (https://git.qemu.org/git/seabios.git/) registered for path 'roms/seabios'
Submodule 'roms/seabios-hppa' (https://git.qemu.org/git/seabios-hppa.git) registered for path 'roms/seabios-hppa'
Submodule 'roms/sgabios' (https://git.qemu.org/git/sgabios.git) registered for path 'roms/sgabios'
Submodule 'roms/skiboot' (https://git.qemu.org/git/skiboot.git) registered for path 'roms/skiboot'
Submodule 'roms/u-boot' (https://git.qemu.org/git/u-boot.git) registered for path 'roms/u-boot'
Submodule 'roms/u-boot-sam460ex' (https://git.qemu.org/git/u-boot-sam460ex.git) registered for path 'roms/u-boot-sam460ex'
Submodule 'slirp' (https://git.qemu.org/git/libslirp.git) registered for path 'slirp'
Submodule 'tests/fp/berkeley-softfloat-3' (https://git.qemu.org/git/berkeley-softfloat-3.git) registered for path 'tests/fp/berkeley-softfloat-3'
Submodule 'tests/fp/berkeley-testfloat-3' (https://git.qemu.org/git/berkeley-testfloat-3.git) registered for path 'tests/fp/berkeley-testfloat-3'
Submodule 'ui/keycodemapdb' (https://git.qemu.org/git/keycodemapdb.git) registered for path 'ui/keycodemapdb'
Cloning into 'capstone'...
Submodule path 'capstone': checked out '22ead3e0bfdb87516656453336160e0a37b066bf'
Cloning into 'dtc'...
Submodule path 'dtc': checked out '88f18909db731a627456f26d779445f84e449536'
Cloning into 'roms/QemuMacDrivers'...
Submodule path 'roms/QemuMacDrivers': checked out '90c488d5f4a407342247b9ea869df1c2d9c8e266'
Cloning into 'roms/SLOF'...
Submodule path 'roms/SLOF': checked out 'ba1ab360eebe6338bb8d7d83a9220ccf7e213af3'
Cloning into 'roms/edk2'...
Submodule path 'roms/edk2': checked out '20d2e5a125e34fc8501026613a71549b2a1a3e54'
Submodule 'SoftFloat' (https://github.com/ucb-bar/berkeley-softfloat-3.git) registered for path 'ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3'
Submodule 'CryptoPkg/Library/OpensslLib/openssl' (https://github.com/openssl/openssl) registered for path 'CryptoPkg/Library/OpensslLib/openssl'
Cloning into 'ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3'...
Submodule path 'roms/edk2/ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3': checked out 'b64af41c3276f97f0e181920400ee056b9c88037'
Cloning into 'CryptoPkg/Library/OpensslLib/openssl'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl': checked out '50eaac9f3337667259de725451f201e784599687'
Submodule 'boringssl' (https://boringssl.googlesource.com/boringssl) registered for path 'boringssl'
Submodule 'krb5' (https://github.com/krb5/krb5) registered for path 'krb5'
Submodule 'pyca.cryptography' (https://github.com/pyca/cryptography.git) registered for path 'pyca-cryptography'
Cloning into 'boringssl'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/boringssl': checked out '2070f8ad9151dc8f3a73bffaa146b5e6937a583f'
Cloning into 'krb5'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/krb5': checked out 'b9ad6c49505c96a088326b62a52568e3484f2168'
Cloning into 'pyca-cryptography'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/pyca-cryptography': checked out '09403100de2f6f1cdd0d484dcb8e620f1c335c8f'
Cloning into 'roms/ipxe'...
Submodule path 'roms/ipxe': checked out 'de4565cbe76ea9f7913a01f331be3ee901bb6e17'
Cloning into 'roms/openbios'...
Submodule path 'roms/openbios': checked out 'c79e0ecb84f4f1ee3f73f521622e264edd1bf174'
Cloning into 'roms/openhackware'...
Submodule path 'roms/openhackware': checked out 'c559da7c8eec5e45ef1f67978827af6f0b9546f5'
Cloning into 'roms/opensbi'...
Submodule path 'roms/opensbi': checked out 'ce228ee0919deb9957192d723eecc8aaae2697c6'
Cloning into 'roms/qemu-palcode'...
Submodule path 'roms/qemu-palcode': checked out 'bf0e13698872450164fa7040da36a95d2d4b326f'
Cloning into 'roms/seabios'...
Submodule path 'roms/seabios': checked out 'a5cab58e9a3fb6e168aba919c5669bea406573b4'
Cloning into 'roms/seabios-hppa'...
Submodule path 'roms/seabios-hppa': checked out '0f4fe84658165e96ce35870fd19fc634e182e77b'
Cloning into 'roms/sgabios'...
Submodule path 'roms/sgabios': checked out 'cbaee52287e5f32373181cff50a00b6c4ac9015a'
Cloning into 'roms/skiboot'...
Submodule path 'roms/skiboot': checked out '261ca8e779e5138869a45f174caa49be6a274501'
Cloning into 'roms/u-boot'...
Submodule path 'roms/u-boot': checked out 'd3689267f92c5956e09cc7d1baa4700141662bff'
Cloning into 'roms/u-boot-sam460ex'...
Submodule path 'roms/u-boot-sam460ex': checked out '60b3916f33e617a815973c5a6df77055b2e3a588'
Cloning into 'slirp'...
Submodule path 'slirp': checked out 'f0da6726207b740f6101028b2992f918477a4b08'
Cloning into 'tests/fp/berkeley-softfloat-3'...
Submodule path 'tests/fp/berkeley-softfloat-3': checked out 'b64af41c3276f97f0e181920400ee056b9c88037'
Cloning into 'tests/fp/berkeley-testfloat-3'...
Submodule path 'tests/fp/berkeley-testfloat-3': checked out '5a59dcec19327396a011a17fd924aed4fec416b3'
Cloning into 'ui/keycodemapdb'...
Submodule path 'ui/keycodemapdb': checked out '6b3d716e2b6472eb7189d3220552280ef3d832ce'
Switched to a new branch 'test'

=== OUTPUT BEGIN ===
checkpatch.pl: no revisions returned for revlist '1'
=== OUTPUT END ===

Test command exited with code: 255


The full log is available at
http://patchew.org/logs/20190731091933.17363-1-ppandit@redhat.com/testing.checkpatch/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com

Re: [Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls

[Markus Armbruster]

P J P <ppandit@redhat.com> writes:

> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> When invoking qemu-bridge-helper in 'net_bridge_run_helper',
> instead of using fixed sized buffers, use dynamically allocated
> ones initialised and returned by g_strdup_printf().

Does this fix a bug?

> If bridge name 'br_buf' is undefined, pass empty string ("") to
> g_strdup_printf() in its place, to avoid printing "(null)" string.
>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  net/tap.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
>
> Update v5: add commit message about conditional 'br_buf' argument
>   -> https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg06397.html
>
> diff --git a/net/tap.c b/net/tap.c
> index e8aadd8d4b..fc38029f41 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -498,9 +498,9 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
>      }
>      if (pid == 0) {
>          int open_max = sysconf(_SC_OPEN_MAX), i;
> -        char fd_buf[6+10];
> -        char br_buf[6+IFNAMSIZ] = {0};
> -        char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
> +        char *fd_buf = NULL;

Dead initializer.

> +        char *br_buf = NULL;
> +        char *helper_cmd = NULL;

Another one.

>  
>          for (i = 3; i < open_max; i++) {
>              if (i != sv[1]) {
> @@ -508,17 +508,17 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
>              }
>          }
>  
> -        snprintf(fd_buf, sizeof(fd_buf), "%s%d", "--fd=", sv[1]);
> +        fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);

Good opportunity to change this to

           fd_buf = g_strdup_printf("--fd=%d", sv[1]);

More of the same below.

>  
>          if (strrchr(helper, ' ') || strrchr(helper, '\t')) {
>              /* assume helper is a command */
>  
>              if (strstr(helper, "--br=") == NULL) {
> -                snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
> +                br_buf = g_strdup_printf("%s%s", "--br=", bridge);
>              }
>  
> -            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s",
> -                     helper, "--use-vnet", fd_buf, br_buf);
> +            helper_cmd = g_strdup_printf("%s %s %s %s", helper,
> +                            "--use-vnet", fd_buf, br_buf ? br_buf : "");
>  
>              parg = args;
>              *parg++ = (char *)"sh";
> @@ -527,10 +527,11 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
>              *parg++ = NULL;
>  
>              execv("/bin/sh", args);
> +            g_free(helper_cmd);
>          } else {
>              /* assume helper is just the executable path name */
>  
> -            snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
> +            br_buf = g_strdup_printf("%s%s", "--br=", bridge);
>  
>              parg = args;
>              *parg++ = (char *)helper;
> @@ -541,6 +542,8 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
>  
>              execv(helper, args);
>          }
> +        g_free(fd_buf);
> +        g_free(br_buf);
>          _exit(1);
>  
>      } else {

The commit does what it claims to do, and no more, so
Reviewed-by: Markus Armbruster <armbru@redhat.com>

However, the code is still rather ugly, and I'd be tempted to use the
opportunity to clean up some more.  Untested sketch:

diff --git a/net/tap.c b/net/tap.c
index 06af8fb8ad..57bb4c552d 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -402,8 +402,7 @@ static void launch_script(const char *setup_script, const char *ifname,
                           int fd, Error **errp)
 {
     int pid, status;
-    char *args[3];
-    char **parg;
+    const char *argv[3];
 
     /* try to launch network script */
     pid = fork();
@@ -413,18 +412,18 @@ static void launch_script(const char *setup_script, const char *ifname,
         return;
     }
     if (pid == 0) {
-        int open_max = sysconf(_SC_OPEN_MAX), i;
+        int open_max = sysconf(_SC_OPEN_MAX);
+        int i;
 
         for (i = 3; i < open_max; i++) {
             if (i != fd) {
                 close(i);
             }
         }
-        parg = args;
-        *parg++ = (char *)setup_script;
-        *parg++ = (char *)ifname;
-        *parg = NULL;
-        execv(setup_script, args);
+        argv[0] = setup_script;
+        argv[1] = ifname;
+        argv[2] = NULL;
+        execv(setup_script, (char *const *)argv);
         _exit(1);
     } else {
         while (waitpid(pid, &status, 0) != pid) {
@@ -478,8 +477,7 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
 {
     sigset_t oldmask, mask;
     int pid, status;
-    char *args[5];
-    char **parg;
+    const char *argv[5];
     int sv[2];
 
     sigemptyset(&mask);
@@ -498,10 +496,9 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
         return -1;
     }
     if (pid == 0) {
-        int open_max = sysconf(_SC_OPEN_MAX), i;
-        char fd_buf[6+10];
-        char br_buf[6+IFNAMSIZ] = {0};
-        char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
+        int open_max = sysconf(_SC_OPEN_MAX);
+        int i;
+        char *fd_opt, *br_opt;
 
         for (i = 3; i < open_max; i++) {
             if (i != sv[1]) {
@@ -509,39 +506,30 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
             }
         }
 
-        snprintf(fd_buf, sizeof(fd_buf), "%s%d", "--fd=", sv[1]);
+        fd_opt = g_strdup_printf("--fd=%d", sv[1]);
+        br_opt = g_strdup_printf("--br=%s", bridge);
 
         if (strrchr(helper, ' ') || strrchr(helper, '\t')) {
             /* assume helper is a command */
-
-            if (strstr(helper, "--br=") == NULL) {
-                snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
-            }
-
-            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s",
-                     helper, "--use-vnet", fd_buf, br_buf);
-
-            parg = args;
-            *parg++ = (char *)"sh";
-            *parg++ = (char *)"-c";
-            *parg++ = helper_cmd;
-            *parg++ = NULL;
-
-            execv("/bin/sh", args);
+            /* FIXME strstr() is lazy and somewhat fragile */
+            bool need_br = !strstr(helper, "--br=");
+
+            argv[0] = "/bin/sh";
+            argv[1] = "-c";
+            argv[2] = g_strdup_printf("%s --use-vnet %s %s",
+                                      helper, fd_opt,
+                                      need_br ? br_opt : "");
+            argv[3] = NULL;
         } else {
             /* assume helper is just the executable path name */
-
-            snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
-
-            parg = args;
-            *parg++ = (char *)helper;
-            *parg++ = (char *)"--use-vnet";
-            *parg++ = fd_buf;
-            *parg++ = br_buf;
-            *parg++ = NULL;
-
-            execv(helper, args);
+            argv[0] = helper;
+            argv[1] = "--use-vnet";
+            argv[2] = fd_opt;
+            argv[3] = br_opt;
+            argv[4] = NULL;
         }
+
+        execv(argv[0], (char *const *)argv);
         _exit(1);
 
     } else {

Re: [Qemu-devel] [PATCH v5] net: tap: replace snprintf with g_strdup_printf calls

[P J P]

+-- On Wed, 31 Jul 2019, Markus Armbruster wrote --+
| However, the code is still rather ugly, and I'd be tempted to use the
| opportunity to clean up some more.  Untested sketch:

Patch v3 did a similar change 
  -> https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg00578.html

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F