Messages in this thread Patch in this message |  | | From | Dominique Martinet <> | Subject | [PATCH] strparser: remove any offset before parsing messages | Date | Tue, 21 Aug 2018 14:51:46 +0200 |
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Offset is not well handled by strparser users right now.
Out of the current strparser users, we have: - tls, that handles offset properly in parse and rcv callbacks - kcm, that handles offset in rcv but not in parse - bpf sockmap, that does not seem to handle offset anywhere
Calling pskb_pull() on new skb ensures that the offset will be 0 everywhere in practice, and in particular for the parse function, unless the user modifies it themselves like tls does.
This fixes a bug which can be exhibited by implementing a simple kcm parser that looks for the packet size in the first word of the packet, and sending two such packets in a single write() call on the other side: the second message will be cut at the length of the first message. Since this is a stream protocol, all the following messages will also be corrupt since it will start looking for the next offset at a wrong position.
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org> ---
I haven't had any comment on v0, so here is what I had planned as refactoring anyawy, but I'd *really* like some opinion on this as a whole...
Also note that compiling bpf programs with libbcc is currently broken in linus' master, see the fix thread here: https://lkml.kernel.org/r/1534834088-15835-1-git-send-email-yamada.masahiro@socionext.com You can likely just revert cafa0010cd51 ("Raise the minimum required gcc version to 4.6") localy meanwhile, or base the patch off 4.18.
net/strparser/strparser.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c index da1a676860ca..d7fb30b1bcfc 100644 --- a/net/strparser/strparser.c +++ b/net/strparser/strparser.c @@ -201,7 +201,17 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb, strp->skb_nextp = NULL; stm = _strp_msg(head); memset(stm, 0, sizeof(*stm)); - stm->strp.offset = orig_offset + eaten; + + /* Can only parse if there is no offset */ + if (unlikely(orig_offset + eaten)) { + if (!pskb_pull(skb, orig_offset + eaten)) { + STRP_STATS_INCR(strp->stats.mem_fail); + strp_parser_err(strp, -ENOMEM, desc); + break; + } + orig_len -= eaten; + orig_offset = eaten = 0; + } } else { /* Unclone if we are appending to an skb that we * already share a frag_list with. @@ -253,8 +263,7 @@ static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb, STRP_STATS_INCR(strp->stats.msg_too_big); strp_parser_err(strp, -EMSGSIZE, desc); break; - } else if (len <= (ssize_t)head->len - - skb->len - stm->strp.offset) { + } else if (len <= (ssize_t)head->len - skb->len) { /* Length must be into new skb (and also * greater than zero) */ -- 2.17.1
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