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SubjectRe: [PATCH] um: remove uses of variable length arrays
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On 12/03/2019 13:30, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@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 <bgolaszewski@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/

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