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authorEric Biggers <ebiggers@google.com>2020-10-26 13:07:15 -0700
committerHerbert Xu <herbert@gondor.apana.org.au>2020-11-06 14:29:11 +1100
commit92eb6c3060ebe3adf381fd9899451c5b047bb14d (patch)
tree3a436c68a50baf44e5ec55bced20bf7008576fcb
parent2d653936eb2cf613526290caa512b46e4c0d71ae (diff)
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: <stable@vger.kernel.org> # v4.12+ Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
-rw-r--r--crypto/af_alg.c10
-rw-r--r--include/uapi/linux/if_alg.h16
2 files changed, 23 insertions, 3 deletions
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) {
diff --git a/include/uapi/linux/if_alg.h b/include/uapi/linux/if_alg.h
index 60b7c2efd921..dc52a11ba6d1 100644
--- 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];