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kernel/relay.c: fix read_pos error when multiple readers

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When reading, read_pos should start with bytes_consumed, not file->f_pos.
Because when there is more than one reader, the read_pos corresponding to
file->f_pos may have been consumed, which will cause the data that has
been consumed to be read and the bytes_consumed update error.

Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jann Horn <jannh@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>e
Link: http://lkml.kernel.org/r/1579691175-28949-1-git-send-email-yangpc@wangsu.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Pengcheng Yang 2020-06-04 16:51:30 -07:00 committed by Linus Torvalds
parent 54e200ab40
commit 341a7213e5
1 changed files with 7 additions and 10 deletions
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17
kernel/relay.c
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@ -996,14 +996,14 @@ static void relay_file_read_consume(struct rchan_buf *buf,
/* /*
* relay_file_read_avail - boolean, are there unconsumed bytes available? * relay_file_read_avail - boolean, are there unconsumed bytes available?
*/ */
static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos) static int relay_file_read_avail(struct rchan_buf *buf)
{ {
size_t subbuf_size = buf->chan->subbuf_size; size_t subbuf_size = buf->chan->subbuf_size;
size_t n_subbufs = buf->chan->n_subbufs; size_t n_subbufs = buf->chan->n_subbufs;
size_t produced = buf->subbufs_produced; size_t produced = buf->subbufs_produced;
size_t consumed = buf->subbufs_consumed; size_t consumed = buf->subbufs_consumed;
relay_file_read_consume(buf, read_pos, 0); relay_file_read_consume(buf, 0, 0);
consumed = buf->subbufs_consumed; consumed = buf->subbufs_consumed;
@ -1064,23 +1064,20 @@ static size_t relay_file_read_subbuf_avail(size_t read_pos,
/** /**
* relay_file_read_start_pos - find the first available byte to read * relay_file_read_start_pos - find the first available byte to read
* @read_pos: file read position
* @buf: relay channel buffer * @buf: relay channel buffer
* *
* If the @read_pos is in the middle of padding, return the * If the read_pos is in the middle of padding, return the
* position of the first actually available byte, otherwise * position of the first actually available byte, otherwise
* return the original value. * return the original value.
*/ */
static size_t relay_file_read_start_pos(size_t read_pos, static size_t relay_file_read_start_pos(struct rchan_buf *buf)
struct rchan_buf *buf)
{ {
size_t read_subbuf, padding, padding_start, padding_end; size_t read_subbuf, padding, padding_start, padding_end;
size_t subbuf_size = buf->chan->subbuf_size; size_t subbuf_size = buf->chan->subbuf_size;
size_t n_subbufs = buf->chan->n_subbufs; size_t n_subbufs = buf->chan->n_subbufs;
size_t consumed = buf->subbufs_consumed % n_subbufs; size_t consumed = buf->subbufs_consumed % n_subbufs;
size_t read_pos = consumed * subbuf_size + buf->bytes_consumed;
if (!read_pos)
read_pos = consumed * subbuf_size + buf->bytes_consumed;
read_subbuf = read_pos / subbuf_size; read_subbuf = read_pos / subbuf_size;
padding = buf->padding[read_subbuf]; padding = buf->padding[read_subbuf];
padding_start = (read_subbuf + 1) * subbuf_size - padding; padding_start = (read_subbuf + 1) * subbuf_size - padding;
@ -1136,10 +1133,10 @@ static ssize_t relay_file_read(struct file *filp,
do { do {
void *from; void *from;
if (!relay_file_read_avail(buf, *ppos)) if (!relay_file_read_avail(buf))
break; break;
read_start = relay_file_read_start_pos(*ppos, buf); read_start = relay_file_read_start_pos(buf);
avail = relay_file_read_subbuf_avail(read_start, buf); avail = relay_file_read_subbuf_avail(read_start, buf);
if (!avail) if (!avail)
break; break;