From 92eb6c3060ebe3adf381fd9899451c5b047bb14d Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 26 Oct 2020 13:07:15 -0700 Subject: crypto: af_alg - avoid undefined behavior accessing salg_name Commit 3f69cc60768b ("crypto: af_alg - Allow arbitrarily long algorithm names") made the kernel start accepting arbitrarily long algorithm names in sockaddr_alg. However, the actual length of the salg_name field stayed at the original 64 bytes. This is broken because the kernel can access indices >= 64 in salg_name, which is undefined behavior -- even though the memory that is accessed is still located within the sockaddr structure. It would only be defined behavior if the array were properly marked as arbitrary-length (either by making it a flexible array, which is the recommended way these days, or by making it an array of length 0 or 1). We can't simply change salg_name into a flexible array, since that would break source compatibility with userspace programs that embed sockaddr_alg into another struct, or (more commonly) declare a sockaddr_alg like 'struct sockaddr_alg sa = { .salg_name = "foo" };'. One solution would be to change salg_name into a flexible array only when '#ifdef __KERNEL__'. However, that would keep userspace without an easy way to actually use the longer algorithm names. Instead, add a new structure 'sockaddr_alg_new' that has the flexible array field, and expose it to both userspace and the kernel. Make the kernel use it correctly in alg_bind(). This addresses the syzbot report "UBSAN: array-index-out-of-bounds in alg_bind" (https://syzkaller.appspot.com/bug?extid=92ead4eb8e26a26d465e). Reported-by: syzbot+92ead4eb8e26a26d465e@syzkaller.appspotmail.com Fixes: 3f69cc60768b ("crypto: af_alg - Allow arbitrarily long algorithm names") Cc: # v4.12+ Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- crypto/af_alg.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'crypto/af_alg.c') diff --git a/crypto/af_alg.c b/crypto/af_alg.c index d11db80d24cd..9acb9d2c4bcf 100644 --- a/crypto/af_alg.c +++ b/crypto/af_alg.c @@ -147,7 +147,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) const u32 allowed = CRYPTO_ALG_KERN_DRIVER_ONLY; struct sock *sk = sock->sk; struct alg_sock *ask = alg_sk(sk); - struct sockaddr_alg *sa = (void *)uaddr; + struct sockaddr_alg_new *sa = (void *)uaddr; const struct af_alg_type *type; void *private; int err; @@ -155,7 +155,11 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) if (sock->state == SS_CONNECTED) return -EINVAL; - if (addr_len < sizeof(*sa)) + BUILD_BUG_ON(offsetof(struct sockaddr_alg_new, salg_name) != + offsetof(struct sockaddr_alg, salg_name)); + BUILD_BUG_ON(offsetof(struct sockaddr_alg, salg_name) != sizeof(*sa)); + + if (addr_len < sizeof(*sa) + 1) return -EINVAL; /* If caller uses non-allowed flag, return error. */ @@ -163,7 +167,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) return -EINVAL; sa->salg_type[sizeof(sa->salg_type) - 1] = 0; - sa->salg_name[sizeof(sa->salg_name) + addr_len - sizeof(*sa) - 1] = 0; + sa->salg_name[addr_len - sizeof(*sa) - 1] = 0; type = alg_get_type(sa->salg_type); if (PTR_ERR(type) == -ENOENT) { -- cgit v1.2.3