linux-hardening - Re: [PATCH][next] udf: Fix -Wstringop-overflow warnings

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Date:   Mon, 31 Jul 2023 16:35:23 +0200
From:   Jan Kara <jack@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jan Kara <jack@...e.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] udf: Fix -Wstringop-overflow warnings

On Wed 12-07-23 12:05:34, Kees Cook wrote:
> On Wed, Jul 12, 2023 at 12:25:45PM -0600, Gustavo A. R. Silva wrote:
> > Use unsigned type in call to macro mint_t(). This avoids confusing the
> > compiler about possible negative values that would cause the value in
> > _len_ to wrap around.
> > 
> > Fixes the following -Wstringop-warnings seen when building ARM
> > architecture with allyesconfig (GCC 13):
> > fs/udf/directory.c: In function 'udf_copy_fi':
> > include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' specified bound between 2147483648 and 4294967295 exceeds maximum object size 2147483647 [-Wstringop-overflow=]
> >    57 | #define __underlying_memcpy     __builtin_memcpy
> >       |                                 ^
> > include/linux/fortify-string.h:648:9: note: in expansion of macro '__underlying_memcpy'
> >   648 |         __underlying_##op(p, q, __fortify_size);                        \
> >       |         ^~~~~~~~~~~~~
> > include/linux/fortify-string.h:693:26: note: in expansion of macro '__fortify_memcpy_chk'
> >   693 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
> >       |                          ^~~~~~~~~~~~~~~~~~~~
> > fs/udf/directory.c:99:9: note: in expansion of macro 'memcpy'
> >    99 |         memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
> >       |         ^~~~~~
> > include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' specified bound between 2147483648 and 4294967295 exceeds maximum object size 2147483647 [-Wstringop-overflow=]
> >    57 | #define __underlying_memcpy     __builtin_memcpy
> >       |                                 ^
> > include/linux/fortify-string.h:648:9: note: in expansion of macro '__underlying_memcpy'
> >   648 |         __underlying_##op(p, q, __fortify_size);                        \
> >       |         ^~~~~~~~~~~~~
> > include/linux/fortify-string.h:693:26: note: in expansion of macro '__fortify_memcpy_chk'
> >   693 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
> >       |                          ^~~~~~~~~~~~~~~~~~~~
> > fs/udf/directory.c:99:9: note: in expansion of macro 'memcpy'
> >    99 |         memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
> >       |         ^~~~~~
> >   AR      fs/udf/built-in.a
> > 
> > This helps with the ongoing efforts to globally enable
> > -Wstringop-overflow.
> > 
> > Link: https://github.com/KSPP/linux/issues/329
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> > ---
> >  fs/udf/directory.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/udf/directory.c b/fs/udf/directory.c
> > index 1c775e072b2f..93153665eb37 100644
> > --- a/fs/udf/directory.c
> > +++ b/fs/udf/directory.c
> > @@ -95,7 +95,7 @@ static int udf_copy_fi(struct udf_fileident_iter *iter)
> >  	}
> >  
> >  	off = iter->pos & (blksize - 1);
> > -	len = min_t(int, sizeof(struct fileIdentDesc), blksize - off);
> > +	len = min_t(u32, sizeof(struct fileIdentDesc), blksize - off);
> >  	memcpy(&iter->fi, iter->bh[0]->b_data + off, len);
> >  	if (len < sizeof(struct fileIdentDesc))
> >  		memcpy((char *)(&iter->fi) + len, iter->bh[1]->b_data,
> 
> len is u32, "off" can't be less than blksize, so this all looks correct
> to me. Thanks!
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

Thanks! I've merged the patch to my tree.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR