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[PATCH 3.18 41/42] bcache: fix bch_hprint crash and improve output

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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Lyle <mlyle@lyle.org>

commit 9276717b9e297a62d1151a43d1cd286213f68eb7 upstream.

Most importantly, solve a crash where %llu was used to format signed
numbers.  This would cause a buffer overflow when reading sysfs
writeback_rate_debug, as only 20 bytes were allocated for this and
%llu writes 20 characters plus a null.

Always use the units mechanism rather than having different output
paths for simplicity.

Also, correct problems with display output where 1.10 was a larger
number than 1.09, by multiplying by 10 and then dividing by 1024 instead
of dividing by 100.  (Remainders of >= 1000 would print as .10).

Minor changes: Always display the decimal point instead of trying to
omit it based on number of digits shown.  Decide what units to use
based on 1000 as a threshold, not 1024 (in other words, always print
at most 3 digits before the decimal point).

Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reported-by: Dmitry Yu Okunev <dyokunev@ut.mephi.ru>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/util.c |   46 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 13 deletions(-)

--- a/drivers/md/bcache/util.c
+++ b/drivers/md/bcache/util.c
@@ -73,24 +73,44 @@ STRTO_H(strtouint, unsigned int)
 STRTO_H(strtoll, long long)
 STRTO_H(strtoull, unsigned long long)
 
+/**
+ * bch_hprint() - formats @v to human readable string for sysfs.
+ *
+ * @v - signed 64 bit integer
+ * @buf - the (at least 8 byte) buffer to format the result into.
+ *
+ * Returns the number of bytes used by format.
+ */
 ssize_t bch_hprint(char *buf, int64_t v)
 {
 	static const char units[] = "?kMGTPEZY";
-	char dec[4] = "";
-	int u, t = 0;
+	int u = 0, t;
 
-	for (u = 0; v >= 1024 || v <= -1024; u++) {
-		t = v & ~(~0 << 10);
-		v >>= 10;
-	}
+	uint64_t q;
 
-	if (!u)
-		return sprintf(buf, "%llu", v);
-
-	if (v < 100 && v > -100)
-		snprintf(dec, sizeof(dec), ".%i", t / 100);
-
-	return sprintf(buf, "%lli%s%c", v, dec, units[u]);
+	if (v < 0)
+		q = -v;
+	else
+		q = v;
+
+	/* For as long as the number is more than 3 digits, but at least
+	 * once, shift right / divide by 1024.  Keep the remainder for
+	 * a digit after the decimal point.
+	 */
+	do {
+		u++;
+
+		t = q & ~(~0 << 10);
+		q >>= 10;
+	} while (q >= 1000);
+
+	if (v < 0)
+		/* '-', up to 3 digits, '.', 1 digit, 1 character, null;
+		 * yields 8 bytes.
+		 */
+		return sprintf(buf, "-%llu.%i%c", q, t * 10 / 1024, units[u]);
+	else
+		return sprintf(buf, "%llu.%i%c", q, t * 10 / 1024, units[u]);
 }
 
 ssize_t bch_snprint_string_list(char *buf, size_t size, const char * const list[],

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[PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 11/42] [PATCH - RESEND] crypto: AF_ALG - remove SGL terminator indicator when  chaining Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 25/42] scsi: sg: use standard lists for sg_requests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 03/42] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 42/42] mac80211: flush hw_roc_start work before cancelling the ROC Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 05/42] ipv6: fix memory leak with multiple tables during netns destruction Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 27/42] scsi: sg: factor out sg_fill_request_table() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 12/42] ext4: fix incorrect quotaoff if the quota feature is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 01/42] ipv6: accept 64k - 1 packet length in ip6_find_1stfragopt() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 21/42] scsi: zfcp: fix payload with full FCP_RSP IU in SCSI trace records Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 29/42] scsi: qla2xxx: Fix an integer overflow in sysfs code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 08/42] [PATCH] Revert "usb: musb: fix tx fifo flush handling again" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 16/42] skd: Avoid that module unloading triggers a use-after-free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 30/42] ftrace: Fix selftest goto location on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 07/42] f2fs: check hot_data for roll-forward recovery Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 37/42] bcache: Fix leak of bdev reference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 40/42] bcache: fix for gc and write-back race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 39/42] bcache: Correct return value for sysfs attach errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 41/42] bcache: fix bch_hprint crash and improve output Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 33/42] PCI: shpchp: Enable bridge bus mastering if MSI is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 06/42] ipv6: fix typo in fib6_net_exit() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 31/42] tracing: Apply trace_clock changes to instance max buffer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 38/42] bcache: correct cache_dirty_target in __update_writeback_rate() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 32/42] ARC: Re-enable MMU upon Machine Check exception Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 28/42] scsi: sg: fixup infoleak when using SG_GET_REQUEST_TABLE Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 34/42] media: v4l2-compat-ioctl32: Fix timespec conversion Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 04/42] tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 35/42] media: uvcvideo: Prevent heap overflow when accessing mapped controls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 24/42] scsi: sg: remove save_scat_len Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 14/42] block: Relax a check in blk_start_queue() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 18/42] scsi: zfcp: fix queuecommand for scsi_eh commands when DIX enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 22/42] scsi: zfcp: trace HBA FSF response by default on dismiss or timedout late response Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 26/42] scsi: sg: off by one in sg_ioctl() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 23/42] scsi: zfcp: trace high part of "new" 64 bit SCSI LUN Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 02/42] qlge: avoid memcpy buffer overflow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 13/42] powerpc: Fix DAR reporting when alignment handler faults Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 03:10 +0200
    Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 08:40 +0200
      Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 13:10 +0200
        Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 14:30 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-09-26 01:20 +0200

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