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Miao Wang reported a bug of SO_PEEK_OFF on AF_UNIX SOCK_STREAM
socket.
The unexpected behaviour is triggered when the peek offset is
larger than the recv queue and the thread is unblocked by new
data.
Let's assume a socket which has "aaaa" in the recv queue and
the peek offset is 4.
First, unix_stream_read_generic() reads the offset 4 and skips
the skb(s) of "aaaa" with the code below:
skip = max(sk_peek_offset(sk, flags), 0); /* @skip is 4. */
do {
...
while (skip >= unix_skb_len(skb)) {
skip -= unix_skb_len(skb);
...
skb = skb_peek_next(skb, &sk->sk_receive_queue);
if (!skb)
goto again; /* @skip is 0. */
}
The thread jumps to the 'again' label and goes to sleep since
new data has not arrived yet.
Later, new data "bbbb" unblocks the thread, and the thread jumps
to the 'redo:' label to restart the entire process from the first
skb in the recv queue.
do {
...
redo:
...
last = skb = skb_peek(&sk->sk_receive_queue);
...
again:
if (skb == NULL) {
...
timeo = unix_stream_data_wait(sk, timeo, last,
last_len, freezable);
...
goto redo; /* @skip is 0 !! */
However, the peek offset is not reset in the path.
If the buffer size is 8, recv() will return "aaaabbbb" without
skipping any data, and the final offset will be 12 (the original
offset 4 + peeked skbs' length 8).
After sleeping in unix_stream_read_generic(), we have to fetch the
peek offset again.
Let's move the redo label before mutex_lock(&u->iolock).
Fixes:
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||
|---|---|---|
| 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 | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .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 reStructuredText 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.