From: Eric Biggers ebiggers@google.com
commit 92eb6c3060ebe3adf381fd9899451c5b047bb14d upstream.
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: stable@vger.kernel.org # v4.12+ Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- crypto/af_alg.c | 10 +++++++--- include/uapi/linux/if_alg.h | 16 ++++++++++++++++ 2 files changed, 23 insertions(+), 3 deletions(-)
--- a/crypto/af_alg.c +++ b/crypto/af_alg.c @@ -151,7 +151,7 @@ static int alg_bind(struct socket *sock, 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; @@ -159,7 +159,11 @@ static int alg_bind(struct socket *sock, 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. */ @@ -167,7 +171,7 @@ static int alg_bind(struct socket *sock, 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 (IS_ERR(type) && PTR_ERR(type) == -ENOENT) { --- a/include/uapi/linux/if_alg.h +++ b/include/uapi/linux/if_alg.h @@ -24,6 +24,22 @@ struct sockaddr_alg { __u8 salg_name[64]; };
+/* + * Linux v4.12 and later removed the 64-byte limit on salg_name[]; it's now an + * arbitrary-length field. We had to keep the original struct above for source + * compatibility with existing userspace programs, though. Use the new struct + * below if support for very long algorithm names is needed. To do this, + * allocate 'sizeof(struct sockaddr_alg_new) + strlen(algname) + 1' bytes, and + * copy algname (including the null terminator) into salg_name. + */ +struct sockaddr_alg_new { + __u16 salg_family; + __u8 salg_type[14]; + __u32 salg_feat; + __u32 salg_mask; + __u8 salg_name[]; +}; + struct af_alg_iv { __u32 ivlen; __u8 iv[0];