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author | Eric Biggers <ebiggers@google.com> | 2020-10-26 23:07:15 +0300 |
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committer | Herbert Xu <herbert@gondor.apana.org.au> | 2020-11-06 06:29:11 +0300 |
commit | 92eb6c3060ebe3adf381fd9899451c5b047bb14d (patch) | |
tree | 3a436c68a50baf44e5ec55bced20bf7008576fcb /include/uapi/linux/if_alg.h | |
parent | 2d653936eb2cf613526290caa512b46e4c0d71ae (diff) | |
download | linux-92eb6c3060ebe3adf381fd9899451c5b047bb14d.tar.xz |
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>
Diffstat (limited to 'include/uapi/linux/if_alg.h')
-rw-r--r-- | include/uapi/linux/if_alg.h | 16 |
1 files changed, 16 insertions, 0 deletions
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]; |