On Tue, May 29, 2018 at 12:57 AM, Arnd Bergmann <a...@arndb.de> wrote:
> On Tue, May 29, 2018 at 7:57 AM, Nick Desaulniers
> <nick.desaulni...@gmail.com> wrote:
>> Fixes stringop-truncation and stringop-overflow warnings from gcc-8.
>
> That patch description should really explain whether gcc is right or not.
> What's
> the worst thing that could happen here?
>
> I would also recommend citing the exact warning you got.
>
>> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
>> index ed5d349..b5dfff1 100644
>> --- a/kernel/debug/kdb/kdb_io.c
>> +++ b/kernel/debug/kdb/kdb_io.c
>> @@ -443,7 +443,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
>> char *kdb_getstr(char *buffer, size_t bufsize, const char *prompt)
>> {
>> if (prompt && kdb_prompt_str != prompt)
>> - strncpy(kdb_prompt_str, prompt, CMD_BUFLEN);
>> + strlcpy(kdb_prompt_str, prompt, CMD_BUFLEN);
>> kdb_printf(kdb_prompt_str);
>> kdb_nextline = 1; /* Prompt and input resets line number */
>> return kdb_read(buffer, bufsize);
>> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
>> index e405677..c30a0d8 100644
>> --- a/kernel/debug/kdb/kdb_main.c
>> +++ b/kernel/debug/kdb/kdb_main.c
>> @@ -1103,12 +1103,12 @@ static int handle_ctrl_cmd(char *cmd)
>> case CTRL_P:
>> if (cmdptr != cmd_tail)
>> cmdptr = (cmdptr-1) % KDB_CMD_HISTORY_COUNT;
>> - strncpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
>> + strlcpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
>> return 1;
>> case CTRL_N:
>> if (cmdptr != cmd_head)
>> cmdptr = (cmdptr+1) % KDB_CMD_HISTORY_COUNT;
>> - strncpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
>> + strlcpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
>> return 1;
>> }
>> return 0;
>
> Those three all look good.
>
>> diff --git a/kernel/debug/kdb/kdb_support.c b/kernel/debug/kdb/kdb_support.c
>> index 990b3cc..dcfbf8f 100644
>> --- a/kernel/debug/kdb/kdb_support.c
>> +++ b/kernel/debug/kdb/kdb_support.c
>> @@ -236,7 +236,7 @@ int kallsyms_symbol_next(char *prefix_name, int flag)
>>
>> while ((name = kdb_walk_kallsyms(&pos))) {
>> if (strncmp(name, prefix_name, prefix_len) == 0) {
>> - strncpy(prefix_name, name, strlen(name)+1);
>> + strlcpy(prefix_name, name, prefix_len);
>> return 1;
>> }
>
> I don't know what this does, but you are changing the behavior: the previous
> 'strlen(name)+1' argument was the size of the source string (which makes
> the strncpy() behave the same as a plain strcpy()), the new one means
> we only copy at most as many bytes as the previous length of the destination
> string.
>
> Is that intended? If yes, better explain it in the patch description.
>
> Arnd
Eric points out that this will leak kernel memory if size is less than
sizeof src.
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