[PATCH v3 1/7] crypto: handle zero sized AEAD inputs correctly

[Ard Biesheuvel <ardb@kernel.org>]

There are corner cases where skcipher_walk_aead_[en|de]crypt() may be
invoked with a zero sized input, which is not rejected by the walker
code, but results in the skcipher_walk structure to not be fully
initialized. This will leave stale values in its page and buffer
members, which will be subsequently passed to kfree() or free_page() by
skcipher_walk_done(), resulting in a crash if those routines fail to
identify them as in valid inputs.

Fix this by setting page and buffer to NULL even if the size of the
input is zero.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 crypto/skcipher.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index a15376245416..93fdacf49697 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -511,6 +511,8 @@ static int skcipher_walk_aead_common(struct skcipher_walk *walk,
 	walk->nbytes = 0;
 	walk->iv = req->iv;
 	walk->oiv = req->iv;
+	walk->buffer = NULL;
+	walk->page = NULL;
 
 	if (unlikely(!walk->total))
 		return 0;
-- 
2.20.1


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