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[PATCH 4.9 43/83] ext4: add sanity checking to count_overhead()

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

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

From: Theodore Ts'o <tytso@mit.edu>

commit c48ae41bafe31e9a66d8be2ced4e42a6b57fa814 upstream.

The commit "ext4: sanity check the block and cluster size at mount
time" should prevent any problems, but in case the superblock is
modified while the file system is mounted, add an extra safety check
to make sure we won't overrun the allocated buffer.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext4/super.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3193,10 +3193,15 @@ static int count_overhead(struct super_b
 			ext4_set_bit(s++, buf);
 			count++;
 		}
-		for (j = ext4_bg_num_gdb(sb, grp); j > 0; j--) {
-			ext4_set_bit(EXT4_B2C(sbi, s++), buf);
-			count++;
+		j = ext4_bg_num_gdb(sb, grp);
+		if (s + j > EXT4_BLOCKS_PER_GROUP(sb)) {
+			ext4_error(sb, "Invalid number of block group "
+				   "descriptor blocks: %d", j);
+			j = EXT4_BLOCKS_PER_GROUP(sb) - s;
 		}
+		count += j;
+		for (; j > 0; j--)
+			ext4_set_bit(EXT4_B2C(sbi, s++), buf);
 	}
 	if (!count)
 		return 0;

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[PATCH 4.9 00/83] 4.9.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:20 +0100
  [PATCH 4.9 68/83] CIFS: Fix a possible memory corruption during reconnect Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 26/83] ALSA: hda - Gate the mic jack on HP Z1 Gen3 AiO Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 33/83] mm: Add a user_ns owner to mm_struct and fix ptrace permission checks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 38/83] ext4: dont lock buffer in ext4_commit_super if holding spinlock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 39/83] ext4: fix mballoc breakage with 64k block size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 17/83] usb: gadget: f_uac2: fix error handling at afunc_bind Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 41/83] ext4: use more strict checks for inodes_per_block on mount Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 36/83] ptrace: Dont allow accessing an undumpable mm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 56/83] PM / OPP: Pass opp_table to dev_pm_opp_put_regulator() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 35/83] ptrace: Capture the ptracers creds not PT_PTRACE_CAP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 42/83] ext4: fix in-superblock mount options processing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 40/83] ext4: fix stack memory corruption with 64k block size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 25/83] ALSA: hda - fix headset-mic problem on a Dell laptop Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 64/83] dm raid: fix discard support regression Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 31/83] splice: reinstate SIGPIPE/EPIPE handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 59/83] dm table: fix all_blk_mq inconsistency when an empty table is loaded Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 34/83] vfs,mm: fix return value of read() at s_maxbytes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 54/83] mm, page_alloc: keep pcp count and list contents in sync if struct page is corrupted Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 32/83] block_dev: dont test bdev->bd_contains when it is not stable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 13/83] USB: cdc-acm: add device id for GW Instek AFG-125 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 12/83] USB: serial: kl5kusb105: fix open error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 30/83] fs: exec: apply CLOEXEC before changing dumpable task flags Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 29/83] exec: Ensure mm->user_ns contains the execed files Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 62/83] dm crypt: mark key as invalid until properly loaded Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 28/83] clk: ti: omap36xx: Work around sprz319 advisory 2.1 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 66/83] ASoC: intel: Fix crash at suspend/resume without card registration Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 43/83] ext4: add sanity checking to count_overhead() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 55/83] usb: gadget: composite: always set ep->mult to a sensible value Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  [PATCH 4.9 58/83] blk-mq: Do not invoke .queue_rq() for a stopped queue Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:30 +0100
  Re: [PATCH 4.9 00/83] 4.9.1-stable review Shuah Khan <shuah.kh@samsung.com> - 2017-01-05 01:50 +0100
    Re: [PATCH 4.9 00/83] 4.9.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-05 09:00 +0100
  Re: [PATCH 4.9 00/83] 4.9.1-stable review Guenter Roeck <linux@roeck-us.net> - 2017-01-05 06:00 +0100
    Re: [PATCH 4.9 00/83] 4.9.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-05 09:00 +0100

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