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SubjectRe: [PATCH v2] lib/cmdline: prevent unintented access to address
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On 8/12/20 8:07 PM, Seungil Kang wrote:
> When args = "\"\0", "i" will be 0 and args[i-1] is used. (*lib/cmdline.c +238)
> Because of "i" is an unsigned int type, the function will access at args[0xFFFFFFFF].
> It can make a crash.
>
> Signed-off-by: Seungil Kang <sil.kang@samsung.com>
> ---
>
> Thanks for your review, my comments below
>
>> Can you be less ambiguous with the args value? (Perhaps provide a hexdump of it
> for better understanding)
>
> This kind of args as hexdump below can cause crash.
>
> 00000000: 736f 6d65 7468 696e 6731 3d73 6f6d 655f something1=some_
> 00000010: 7661 6c75 6573 2022 0000 0000 0000 0000 values "
>
> The args end with "\"\0".
>
>> Please, use proper punctuation, I'm lost where is the sentence and what are the
> logical parts of them.
>
> I'm sorry to confuse you. I fix the commit msg
>
>> Can you point out to the code that calls this and leads to a crash?
>
> *lib/cmdlinc + 201 ~, next_arg function with args = "\"\0"
>
> char *next_arg(char *args, char **param, char **val) <-- args = "\"\0".
> {
> unsigned int i, equals = 0;
> int in_quote = 0, quoted = 0;
> char *next;
>
> if (*args == '"') { <-- *args == '"' is a true condition,
> args++; <-- args++, so *args = '\0'.
> in_quote = 1;
> quoted = 1; <-- quoted also set 1.
> }
>
> for (i = 0; args[i]; i++) { <-- when reached this point, i = 0, and arg[0] == '\0',
> so for loop is skipped.
> if (isspace(args[i]) && !in_quote)
> break;
> if (equals == 0) {
> if (args[i] == '=')
> equals = i;
> }
> if (args[i] == '"')
> in_quote = !in_quote;
> }
>
> *param = args;
> if (!equals)
> *val = NULL;
> else {
> args[equals] = '\0';
> *val = args + equals + 1;
>
> /* Don't include quotes in value. */
> if (**val == '"') {
> (*val)++;
> if (args[i-1] == '"')
> args[i-1] = '\0';
> }
> }
> if (quoted && args[i-1] == '"') <-- When reached this point, quoted is still set 1,
> "i" is still 0, and "i" is unsigned int type,
> so address will be {address of args} + 0xFFFFFFFF.
> It can make a crash.
> args[i-1] = '\0';
>
> if (args[i]) {
> args[i] = '\0';
> next = args + i + 1;
> } else
> next = args + i;
>
> /* Chew up trailing spaces. */
> return skip_spaces(next);
> }
>
>
>> Can you provide a KUnit test module which can check the case?
>
> If necessary, I will make it and share it.

Hi,
Have you tested this patch?
If so, how?


>
> lib/cmdline.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/cmdline.c b/lib/cmdline.c
> index fbb9981a04a4..2fd29d7723b2 100644
> --- a/lib/cmdline.c
> +++ b/lib/cmdline.c
> @@ -200,7 +200,7 @@ bool parse_option_str(const char *str, const char *option)
> */
> char *next_arg(char *args, char **param, char **val)
> {
> - unsigned int i, equals = 0;
> + int i, equals = 0;
> int in_quote = 0, quoted = 0;
> char *next;
>
>

thanks.
--
~Randy

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