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Subject: Re: [PATCH] um: remove uses of variable length arrays
To:     Bartosz Golaszewski <brgl@bgdev.pl>
Cc:     Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        linux-um@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20190312133047.16201-1-brgl@bgdev.pl>
 <56704758-ee74-0e9b-de1c-1dc94deda8d7@cambridgegreys.com>
 <CAMRc=MdBsovEpMxwyGmHB_AL=pLtPsE3g=+y1ghYeHhXvobYbw@mail.gmail.com>
From:   Anton Ivanov <anton.ivanov@cambridgegreys.com>
Message-ID: <d574ef46-2935-4afa-c128-8aac74474512@cambridgegreys.com>
Date:   Thu, 14 Mar 2019 13:45:18 +0000
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On 14/03/2019 13:33, Bartosz Golaszewski wrote:
> śr., 13 mar 2019 o 10:45 Anton Ivanov
> <anton.ivanov@cambridgegreys.com> napisał(a):
>> 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.
>>
>> --
> 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/