0f71c9caf2
__ip_append_data() can get into an infinite loop when asked to splice into
a partially-built UDP message that has more than the frag-limit data and up
to the MTU limit. Something like:
pipe(pfd);
sfd = socket(AF_INET, SOCK_DGRAM, 0);
connect(sfd, ...);
send(sfd, buffer, 8161, MSG_CONFIRM|MSG_MORE);
write(pfd[1], buffer, 8);
splice(pfd[0], 0, sfd, 0, 0x4ffe0ul, 0);
where the amount of data given to send() is dependent on the MTU size (in
this instance an interface with an MTU of 8192).
The problem is that the calculation of the amount to copy in
__ip_append_data() goes negative in two places, and, in the second place,
this gets subtracted from the length remaining, thereby increasing it.
This happens when pagedlen > 0 (which happens for MSG_ZEROCOPY and
MSG_SPLICE_PAGES), because the terms in:
copy = datalen - transhdrlen - fraggap - pagedlen;
then mostly cancel when pagedlen is substituted for, leaving just -fraggap.
This causes:
length -= copy + transhdrlen;
to increase the length to more than the amount of data in msg->msg_iter,
which causes skb_splice_from_iter() to be unable to fill the request and it
returns less than 'copied' - which means that length never gets to 0 and we
never exit the loop.
Fix this by:
(1) Insert a note about the dodgy calculation of 'copy'.
(2) If MSG_SPLICE_PAGES, clear copy if it is negative from the above
equation, so that 'offset' isn't regressed and 'length' isn't
increased, which will mean that length and thus copy should match the
amount left in the iterator.
(3) When handling MSG_SPLICE_PAGES, give a warning and return -EIO if
we're asked to splice more than is in the iterator. It might be
better to not give the warning or even just give a 'short' write.
[!] Note that this ought to also affect MSG_ZEROCOPY, but MSG_ZEROCOPY
avoids the problem by simply assuming that everything asked for got copied,
not just the amount that was in the iterator. This is a potential bug for
the future.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.