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List:       linux-hardening
Subject:    Re: [PATCH][next] udf: Fix -Wstringop-overflow warnings
From:       Jan Kara <jack () suse ! cz>
Date:       2023-07-31 14:35:23
Message-ID: 20230731143523.rfmn6oqob7pofyan () quack3
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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@kernel.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@chromium.org>

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

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


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