Re: [PATCH net-next] crypto: Fix af_alg_sendmsg(MSG_SPLICE_PAGES) sglist limit

[Herbert Xu]

On Thu, Jun 15, 2023 at 10:08:54PM +0100, David Howells wrote:
> When af_alg_sendmsg() calls extract_iter_to_sg(), it passes MAX_SGL_ENTS as
> the maximum number of elements that may be written to, but some of the
> elements may already have been used (as recorded in sgl->cur), so
> extract_iter_to_sg() may end up overrunning the scatterlist.
> 
> Fix this to limit the number of elements to "MAX_SGL_ENTS - sgl->cur".
> 
> Note: It probably makes sense in future to alter the behaviour of
> extract_iter_to_sg() to stop if "sgtable->nents >= sg_max" instead, but
> this is a smaller fix for now.
> 
> The bug causes errors looking something like:
> 
> BUG: KASAN: slab-out-of-bounds in sg_assign_page include/linux/scatterlist.h:109 [inline]
> BUG: KASAN: slab-out-of-bounds in sg_set_page include/linux/scatterlist.h:139 [inline]
> BUG: KASAN: slab-out-of-bounds in extract_bvec_to_sg lib/scatterlist.c:1183 [inline]
> BUG: KASAN: slab-out-of-bounds in extract_iter_to_sg lib/scatterlist.c:1352 [inline]
> BUG: KASAN: slab-out-of-bounds in extract_iter_to_sg+0x17a6/0x1960 lib/scatterlist.c:1339
> 
> Fixes: bf63e250c4b1 ("crypto: af_alg: Support MSG_SPLICE_PAGES")
> Reported-by: syzbot+6efc50cc1f8d718d6cb7@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/r/000000000000b2585a05fdeb8379@xxxxxxxxxx/
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Tested-by: syzbot+6efc50cc1f8d718d6cb7@xxxxxxxxxxxxxxxxxxxxxxxxx
> cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> cc: Jens Axboe <axboe@xxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: linux-crypto@xxxxxxxxxxxxxxx
> cc: netdev@xxxxxxxxxxxxxxx
> ---
>  crypto/af_alg.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

Thanks,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt