> On Aug 25, 2020, at 2:01 PM, Paul Cercueil <p...@crapouillou.net> wrote: > > The zstd decompression code, as it is right now, will have internal > values overflow on 32-bit systems when the output size is bigger than > 1 GiB. > > Until someone smarter than me can figure out how to fix the zstd code > properly, limit the destination buffer size to 1 GiB, which should be > enough for everybody, in order to make it usable on 32-bit systems.
I was talking with Yann Collet, and we believe that it isn’t the long that is overflowing, but the pointers. Zstd expects to be given a valid output size. It generally uses a begin/end pointer with its output buffer. So when it is given a very large output size in 32-bit mode the end pointer will overflow the pointer either causing UB, or end pointer < begin pointer, which breaks zstd. Zstd will probably never be able to work properly in this way. A better solution might be to pass MAX_ADDRESS_PTR - OUTPUT_PTR as the size to the __decompress() call. Or some other size that won’t overflow the pointer. Best, Nick > Signed-off-by: Paul Cercueil <p...@crapouillou.net> > Reviewed-by: Nick Terrell <terre...@fb.com> > --- > > Notes: > v2: Change limit to 1 GiB > > lib/decompress_unzstd.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/lib/decompress_unzstd.c b/lib/decompress_unzstd.c > index 0ad2c15479ed..414517baedb0 100644 > --- a/lib/decompress_unzstd.c > +++ b/lib/decompress_unzstd.c > @@ -77,6 +77,7 @@ > > #include <linux/decompress/mm.h> > #include <linux/kernel.h> > +#include <linux/sizes.h> > #include <linux/zstd.h> > > /* 128MB is the maximum window size supported by zstd. */ > @@ -179,7 +180,7 @@ static int INIT __unzstd(unsigned char *in_buf, long > in_len, > size_t ret; > > if (out_len == 0) > - out_len = LONG_MAX; /* no limit */ > + out_len = SZ_1G; /* should be big enough, right? */ > > if (fill == NULL && flush == NULL) > /* > -- > 2.28.0 >
