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 --- include/uapi/linux/if_alg.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'include/uapi/linux/if_alg.h') 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]; -- cgit v1.2.3-59-g8ed1b