kmalloc_flex() in metadata_dst_alloc() sets __counted_by for the
structure to the options_len, which is then initialized to zero.
Later, we're initializing the structure by copying the tunnel info
together with the options, and this triggers a warning for a potential
memcpy overflow, since the compiler estimates that the options can't
fit into the structure, even though the memory for them is actually
allocated.
memcpy: detected buffer overflow: 104 byte write of buffer size 96
WARNING: CPU: X PID: Y at lib/string_helpers.c:1036 __fortify_report
skb_tunnel_info_unclone+0x179/0x190
geneve_xmit+0x7fe/0xe00
The issue is triggered when built with clang and source fortification.
Fix that by doing the copy in two stages: first - the main data with
the options_len, then the options. This way the correct length should
be known at the time of the copy.
It would be better if the options_len never changed after allocation,
but the allocation code is a little separate from the initialization
and it would be awkward and potentially dangerous to return a struct
with options_len set to a non-zero value from the metadata_dst_alloc().
Another option would be to use ip_tunnel_info_opts_set(), but it is
doing too many unnecessary operations for the use case here.
Fixes: 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar
types")
Reported-by: Johan Thomsen <[email protected]>
Closes:
https://lore.kernel.org/netdev/cakv6aam8_ewgxscnkmkym_4swgdvbk++dzfp+y6msuxbp99...@mail.gmail.com/
Signed-off-by: Ilya Maximets <[email protected]>
---
Johan, if you can test this one in your setup as well, that would
be great. Thanks.
include/net/dst_metadata.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
index 1fc2fb03ce3f..f45d1e3163f0 100644
--- a/include/net/dst_metadata.h
+++ b/include/net/dst_metadata.h
@@ -164,8 +164,11 @@ static inline struct metadata_dst *tun_dst_unclone(struct
sk_buff *skb)
if (!new_md)
return ERR_PTR(-ENOMEM);
- memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
- sizeof(struct ip_tunnel_info) + md_size);
+ /* Copy in two stages to keep the __counted_by happy. */
+ new_md->u.tun_info = md_dst->u.tun_info;
+ memcpy(ip_tunnel_info_opts(&new_md->u.tun_info),
+ ip_tunnel_info_opts(&md_dst->u.tun_info), md_size);
+
#ifdef CONFIG_DST_CACHE
/* Unclone the dst cache if there is one */
if (new_md->u.tun_info.dst_cache.cache) {
--
2.54.0
