keys, dns: Fix missing size check of V1 server-list header

The dns_resolver_preparse() function has a check on the size of the
payload for the basic header of the binary-style payload, but is missing
a check for the size of the V1 server-list payload header after
determining that's what we've been given.

Fix this by getting rid of the the pointer to the basic header and just
assuming that we have a V1 server-list payload and moving the V1 server
list pointer inside the if-statement.  Dealing with other types and
versions can be left for when such have been defined.

This can be tested by doing the following with KASAN enabled:

    echo -n -e '\x0\x0\x1\x2' | keyctl padd dns_resolver foo @p

and produces an oops like the following:

    BUG: KASAN: slab-out-of-bounds in dns_resolver_preparse+0xc9f/0xd60 net/dns_resolver/dns_key.c:127
    Read of size 1 at addr ffff888028894084 by task syz-executor265/5069
    ...
    Call Trace:
      dns_resolver_preparse+0xc9f/0xd60 net/dns_resolver/dns_key.c:127
      __key_create_or_update+0x453/0xdf0 security/keys/key.c:842
      key_create_or_update+0x42/0x50 security/keys/key.c:1007
      __do_sys_add_key+0x29c/0x450 security/keys/keyctl.c:134
      do_syscall_x64 arch/x86/entry/common.c:52 [inline]
      do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
      entry_SYSCALL_64_after_hwframe+0x62/0x6a

This patch was originally by Edward Adam Davis, but was modified by
Linus.

Fixes: b946001d3bb1 ("keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry")
Reported-and-tested-by: [email protected]
Link: https://lore.kernel.org/r/[email protected]/
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Edward Adam Davis <[email protected]>
Signed-off-by: David Howells <[email protected]>
Tested-by: David Howells <[email protected]>
Cc: Edward Adam Davis <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: Jeffrey E Altman <[email protected]>
Cc: Wang Lei <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: Steve French <[email protected]>
Cc: Marc Dionne <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions