Re: [PATCH] um: remove uses of variable length arrays

[Anton Ivanov]

On 12/03/2019 13:30, Bartosz Golaszewski wrote:

From: Bartosz Golaszewski <bgolaszew...@baylibre.com>

While the affected code is run in user-mode, the build still warns
about it. Convert all uses of VLA to dynamic allocations.

Signed-off-by: Bartosz Golaszewski <bgolaszew...@baylibre.com>
---
  arch/um/os-Linux/umid.c | 36 +++++++++++++++++++++++++++---------
  1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 998fbb445458..e261656fe9d7 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -135,12 +135,18 @@ static int remove_files_and_dir(char *dir)
   */
  static inline int is_umdir_used(char *dir)
  {
-       char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
-       char pid[sizeof("nnnnn\0")], *end;
+       char pid[sizeof("nnnnn\0")], *end, *file;
        int dead, fd, p, n, err;
+       size_t filelen;

- n = snprintf(file, sizeof(file), "%s/pid", dir);

-       if (n >= sizeof(file)) {
+       err = asprintf(&file, "%s/pid", dir);
+       if (err < 0)
+               return 0;
+
+       filelen = strlen(file);
+
+       n = snprintf(file, filelen, "%s/pid", dir);
+       if (n >= filelen) {
                printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
                err = -E2BIG;
                goto out;
@@ -185,6 +191,7 @@ static inline int is_umdir_used(char *dir)
  out_close:
        close(fd);
  out:
+       free(file);
        return 0;
  }

@@ -210,18 +217,21 @@ static int umdir_take_if_dead(char *dir) static void __init create_pid_file(void)

  {
-       char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
-       char pid[sizeof("nnnnn\0")];
+       char pid[sizeof("nnnnn\0")], *file;
        int fd, n;

- if (umid_file_name("pid", file, sizeof(file)))

+       file = malloc(strlen(uml_dir) + UMID_LEN + sizeof("/pid\0"));
+       if (!file)
                return;

+ if (umid_file_name("pid", file, sizeof(file)))

+               goto out;
+
        fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
        if (fd < 0) {
                printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
                       "%s\n", file, strerror(errno));
-               return;
+               goto out;
        }

snprintf(pid, sizeof(pid), "%d\n", getpid());

@@ -231,6 +241,8 @@ static void __init create_pid_file(void)
                       errno);

close(fd);

+out:
+       free(file);
  }

int __init set_umid(char *name)

@@ -385,13 +397,19 @@ __uml_setup("uml_dir=", set_uml_dir,

static void remove_umid_dir(void)

  {
-       char dir[strlen(uml_dir) + UMID_LEN + 1], err;
+       char *dir, err;
+
+       dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
+       if (!dir)
+               return;

sprintf(dir, "%s%s", uml_dir, umid);

        err = remove_files_and_dir(dir);
        if (err)
                os_warn("%s - remove_files_and_dir failed with err = %d\n",
                        __func__, err);
+
+       free(dir);
  }

__uml_exitcall(remove_umid_dir);

Thanks for bringing it up. It helped me notice that this is actually broken.

PID can be more than 5 digits nowdays.

--
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/