[PATCH 5.4 01/68] floppy: use a statically allocated error counter

Greg Kroah-Hartman
2022-05-23T17:08:06Z

From: Willy Tarreau <w@1wt.eu>

commit f71f01394f742fc4558b3f9f4c7ef4c4cf3b07c8 upstream.

Interrupt handler bad_flp_intr() may cause a UAF on the recently freed
request just to increment the error count. There's no point keeping
that one in the request anyway, and since the interrupt handler uses a
static pointer to the error which cannot be kept in sync with the
pending request, better make it use a static error counter that's reset
for each new request. This reset now happens when entering
redo_fd_request() for a new request via set_next_request().

One initial concern about a single error counter was that errors on one
floppy drive could be reported on another one, but this problem is not
real given that the driver uses a single drive at a time, as that
PC-compatible controllers also have this limitation by using shared
signals. As such the error count is always for the "current" drive.

Reported-by: Minh Yuan <yuanmingbuaa@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Tested-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/block/floppy.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)

--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -521,8 +521,8 @@ static unsigned long fdc_busy;
static DECLARE_WAIT_QUEUE_HEAD(fdc_wait);
static DECLARE_WAIT_QUEUE_HEAD(command_done);

-/* Errors during formatting are counted here. */
-static int format_errors;
+/* errors encountered on the current (or last) request */
+static int floppy_errors;

/* Format request descriptor. */
static struct format_descr format_req;
@@ -542,7 +542,6 @@ static struct format_descr format_req;
static char *floppy_track_buffer;
static int max_buffer_sectors;

-static int *errors;
typedef void (*done_f)(int);
static const struct cont_t {
void (*interrupt)(void);
@@ -1435,7 +1434,7 @@ static int interpret_errors(void)
if (DP->flags & FTD_MSG)
DPRINT("Over/Underrun - retrying\n");
bad = 0;
- } else if (*errors >= DP->max_errors.reporting) {
+ } else if (floppy_errors >= DP->max_errors.reporting) {
print_errors();
}
if (ST2 & ST2_WC || ST2 & ST2_BC)
@@ -2055,7 +2054,7 @@ static void bad_flp_intr(void)
if (!next_valid_format())
return;
}
- err_count = ++(*errors);
+ err_count = ++floppy_errors;
INFBOUND(DRWE->badness, err_count);
if (err_count > DP->max_errors.abort)
cont->done(0);
@@ -2200,9 +2199,8 @@ static int do_format(int drive, struct f
return -EINVAL;
}
format_req = *tmp_format_req;
- format_errors = 0;
cont = &format_cont;
- errors = &format_errors;
+ floppy_errors = 0;
ret = wait_til_done(redo_format, true);
if (ret == -EINTR)
return -EINTR;
@@ -2677,7 +2675,7 @@ static int make_raw_rw_request(void)
*/
if (!direct ||
(indirect * 2 > direct * 3 &&
- *errors < DP->max_errors.read_track &&
+ floppy_errors < DP->max_errors.read_track &&
((!probing ||
(DP->read_track & (1 << DRS->probed_format)))))) {
max_size = blk_rq_sectors(current_req);
@@ -2801,10 +2799,11 @@ static int set_next_request(void)
current_req = list_first_entry_or_null(&floppy_reqs, struct request,
queuelist);
if (current_req) {
- current_req->error_count = 0;
+ floppy_errors = 0;
list_del_init(&current_req->queuelist);
+ return 1;
}
- return current_req != NULL;
+ return 0;
}

static void redo_fd_request(void)
@@ -2860,7 +2859,6 @@ do_request:
_floppy = floppy_type + DP->autodetect[DRS->probed_format];
} else
probing = 0;
- errors = &(current_req->error_count);
tmp = make_raw_rw_request();
if (tmp < 2) {
request_done(tmp);