Re: [PATCH] modpost: fix segfault in sym_is() with prefixed arches

[AmÃrico Wang]

On Thu, Dec 3, 2009 at 11:50 AM, Mike Frysinger <vapier@xxxxxxxxxx> wrote:
> The sym_is() compares a symbol in an attempt to automatically skip symbol
> prefixes. ÂIt does this first by searching the real symbol with the normal
> unprefixed symbol. ÂBut then it uses the length of the original symbol to
> check the end of the substring instead of the length of the symbol it is
> looking for. ÂOn non-prefixed arches, this is effectively the same thing,
> so there is no problem. ÂOn prefixed-arches, since this is exceeds by just
> one byte, a crash is rare and it is usually a NUL byte anyways. ÂBut every
> once in a blue moon, you get the right page alignment and it segfaults.
>
> For example, on the Blackfin arch, sym_is() will be called with the real
> symbol "___mod_usb_device_table" as "symbol" when looking for the normal
> symbol "__mod_usb_device_table" as "name". ÂThe substring will thus return
> one byte into "symbol" and store it into "match". ÂBut then "match" will
> be indexed with the length of "symbol" instead of "name" and so we will
> exceed the storage. Âi.e. the code ends up doing:
> Â Â Â Âchar foo[] = "abc"; return foo[strlen(foo)+1] == '\0';
>
> Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx>
> ---
> Âscripts/mod/file2alias.c | Â Â2 +-
> Â1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
> index 40e0045..1ffd1e4 100644
> --- a/scripts/mod/file2alias.c
> +++ b/scripts/mod/file2alias.c
> @@ -726,7 +726,7 @@ static inline int sym_is(const char *symbol, const char *name)
> Â Â Â Âmatch = strstr(symbol, name);
> Â Â Â Âif (!match)
> Â Â Â Â Â Â Â Âreturn 0;
> - Â Â Â return match[strlen(symbol)] == '\0';
> + Â Â Â return match[strlen(name)] == '\0';
> Â}
>
> Âstatic void do_table(void *symval, unsigned long size,

Nice catch!

Acked-by: WANG Cong <xiyou.wangcong@xxxxxxxxx>
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