On Wed, 2015-01-28 at 16:49 +0100, Rasmus Villemoes wrote: > On Wed, Jan 28 2015, Andy Shevchenko <[email protected]> > wrote: > > > On Wed, 2015-01-28 at 14:25 +0100, Rasmus Villemoes wrote: > >> The helper hex_string() is broken in two ways. First, it doesn't > >> increment buf regardless of whether there is room to print, so callers > >> such as kasprintf() that try to probe the correct storage to allocate > >> will get a too small return value. But even worse, kasprintf() (and > >> likely anyone else trying to find the size of the result) pass NULL > >> for buf and 0 for size, so we also have end == NULL. But this means > >> that the end-1 in hex_string() is (char*)-1, so buf < end-1 is true > >> and we get a NULL pointer deref. I double-checked this with a trivial > >> kernel module that just did a kasprintf(GFP_KERNEL, "%14ph", > >> "CrashBoomBang"). > > > > Good catch, though I don't like the implementation of fix. > > > > What about the following? > > > > > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > > index 8690798..47b36ddd 100644 > > --- a/lib/vsprintf.c > > +++ b/lib/vsprintf.c > > @@ -783,11 +783,20 @@ char *hex_string(char *buf, char *end, u8 *addr, > > struct printf_spec spec, > > if (spec.field_width > 0) > > len = min_t(int, spec.field_width, 64); > > > > - for (i = 0; i < len && buf < end - 1; i++) { > > - buf = hex_byte_pack(buf, addr[i]); > > + for (i = 0; i < len; i++) { > > + if (buf < end) > > + *buf = hex_asc_hi(addr[i]); > > + ++buf; > > + > > + if (buf < end) > > + *buf = hex_asc_lo(addr[i]); > > + ++buf; > > > > - if (buf < end && separator && i != len - 1) > > - *buf++ = separator; > > + if (separator && i != len - 1) { > > + if (buf < end) > > + *buf = separator; > > + ++buf; > > + } > > } > > > > return buf; > > I had exactly that at one point. I think the only reason I ended up > doing it the other way was that I wanted to introduce the write_bytes > helper, and then use that to do some simplifications and optimizations > for other %p helpers. Many of those write their output to a temporary > buffer, knowing exactly how much there is, then delegate to string(), > which then recomputes the string length before printing. But all that > can be done another time, so I'm fine with this also. >
I ACK the version w/o write_bytes() helper. Meanwhile you may submit your helper with usage of it as another patch. -- Andy Shevchenko <[email protected]> Intel Finland Oy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
