On Tue, Aug 26, 2025 at 03:51:04PM +0200, Ard Biesheuvel wrote: > (cc Kees) > > On Sat, 16 Aug 2025 at 11:17, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Sat, Aug 09, 2025 at 05:59:43PM +0800, Edward Adam Davis wrote: > > > Initialize the intermediary array member to 0 to prevent the kernel from > > > leaking uninitialized data to user space. > > > > > > Reported-by: syzbot+e8bcd7ee3db6cb5cb875@xxxxxxxxxxxxxxxxxxxxxxxxx > > > Closes: https://syzkaller.appspot.com/bug?extid=e8bcd7ee3db6cb5cb875 > > > Tested-by: syzbot+e8bcd7ee3db6cb5cb875@xxxxxxxxxxxxxxxxxxxxxxxxx > > > Signed-off-by: Edward Adam Davis <eadavis@xxxxxx> > > > --- > > > crypto/jitterentropy-kcapi.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c > > > index c24d4ff2b4a8..9e9e069f55af 100644 > > > --- a/crypto/jitterentropy-kcapi.c > > > +++ b/crypto/jitterentropy-kcapi.c > > > @@ -107,7 +107,7 @@ int jent_hash_time(void *hash_state, __u64 time, u8 *addtl, > > > { > > > struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state; > > > SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm); > > > - u8 intermediary[SHA3_256_DIGEST_SIZE]; > > > + u8 intermediary[SHA3_256_DIGEST_SIZE] = { 0 }; > > > > This is not a leak! The stack memroy is hashed and fed into the > > entropy pool. > > Is there still a point to doing this now that the compiler > zero-initializes automatic variables? Or does that not apply to u8 > arrays? (asking Kees) Wait, the jitterentropy _depends_ on "uninitialized" stack contents? That is not a safe way to get entropy (especially since the stack contents are likely predictable). But regardless, yes, arrays would be fully wiped by zero-initialized automatic variables. To force it to be uninit, use __uninitialized. -- Kees Cook
