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[PATCH 4.4 36/60] ext4: add sanity checking to count_overhead()

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4.4-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
@@ -3037,10 +3037,15 @@ 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 4.4 00/60] 4.4.40-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:30 +0100
  [PATCH 4.4 47/60] dm flakey: return -EINVAL on interval bounds error in flakey_ctr() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:30 +0100
  [PATCH 4.4 07/60] USB: serial: kl5kusb105: fix open error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 34/60] ext4: use more strict checks for inodes_per_block on mount Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 33/60] ext4: fix stack memory corruption with 64k block size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 36/60] ext4: add sanity checking to count_overhead() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 30/60] ptrace: Capture the ptracers creds not PT_PTRACE_CAP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 18/60] ALSA: hda - Gate the mic jack on HP Z1 Gen3 AiO Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 03/60] btrfs: store and load values of stripes_min/stripes_max in balance status item Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 21/60] Btrfs: fix memory leak in reading btree blocks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 06/60] USB: serial: option: add dlink dwm-158 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 05/60] USB: serial: option: add support for Telit LE922A PIDs 0x1040, 0x1041 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 08/60] USB: cdc-acm: add device id for GW Instek AFG-125 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 32/60] ext4: fix mballoc breakage with 64k block size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 04/60] Btrfs: fix qgroup rescan worker initialization Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 09/60] usb: hub: Fix auto-remount of safely removed or ejected USB-3 devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 35/60] ext4: fix in-superblock mount options processing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:40 +0100
  [PATCH 4.4 15/60] ALSA: hda/ca0132 - Add quirk for Alienware 15 R2 2016 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:50 +0100
  [PATCH 4.4 13/60] ALSA: usb-audio: Add QuickCam Communicate Deluxe/S7500 to volume_control_quirks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 22:50 +0100
  Re: [PATCH 4.4 00/60] 4.4.40-stable review Shuah Khan <shuah.kh@samsung.com> - 2017-01-05 01:50 +0100
  Re: [PATCH 4.4 00/60] 4.4.40-stable review Guenter Roeck <linux@roeck-us.net> - 2017-01-05 06:30 +0100
  Re: [PATCH 4.4 00/60] 4.4.40-stable review Guillaume Nault <g.nault@alphalink.fr> - 2017-01-05 16:50 +0100
    Re: [PATCH 4.4 00/60] 4.4.40-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-05 21:40 +0100

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