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

[Anton Ivanov]

On 14/03/2019 13:33, Bartosz Golaszewski wrote:

śr., 13 mar 2019 o 10:45 Anton Ivanov
<anton.iva...@cambridgegreys.com> napisał(a):

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.

--

Do you want to take this patch anyway and then apply the fix for the
array on top of that or do you prefer it be fixed before that?

Bart

I am OK to take it as is and have the PID length fixed after that.

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