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72 lines
2.5 KiB
Diff
72 lines
2.5 KiB
Diff
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From cde863587b6809fdf61ea3c5391ecf06884b5516 Mon Sep 17 00:00:00 2001
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From: Eryu Guan <guaneryu@gmail.com>
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Date: Thu, 1 Dec 2016 15:08:37 -0500
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Subject: ext4: validate s_first_meta_bg at mount time
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commit 3a4b77cd47bb837b8557595ec7425f281f2ca1fe upstream.
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Ralf Spenneberg reported that he hit a kernel crash when mounting a
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modified ext4 image. And it turns out that kernel crashed when
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calculating fs overhead (ext4_calculate_overhead()), this is because
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the image has very large s_first_meta_bg (debug code shows it's
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842150400), and ext4 overruns the memory in count_overhead() when
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setting bitmap buffer, which is PAGE_SIZE.
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ext4_calculate_overhead():
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buf = get_zeroed_page(GFP_NOFS); <=== PAGE_SIZE buffer
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blks = count_overhead(sb, i, buf);
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count_overhead():
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for (j = ext4_bg_num_gdb(sb, grp); j > 0; j--) { <=== j = 842150400
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ext4_set_bit(EXT4_B2C(sbi, s++), buf); <=== buffer overrun
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count++;
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}
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This can be reproduced easily for me by this script:
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#!/bin/bash
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rm -f fs.img
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mkdir -p /mnt/ext4
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fallocate -l 16M fs.img
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mke2fs -t ext4 -O bigalloc,meta_bg,^resize_inode -F fs.img
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debugfs -w -R "ssv first_meta_bg 842150400" fs.img
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mount -o loop fs.img /mnt/ext4
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Fix it by validating s_first_meta_bg first at mount time, and
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refusing to mount if its value exceeds the largest possible meta_bg
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number.
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Reported-by: Ralf Spenneberg <ralf@os-t.de>
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Signed-off-by: Eryu Guan <guaneryu@gmail.com>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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Reviewed-by: Andreas Dilger <adilger@dilger.ca>
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[bwh: Backported to 3.16: use EXT4_HAS_INCOMPAT_FEATURE()]
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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fs/ext4/super.c | 9 +++++++++
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1 file changed, 9 insertions(+)
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diff --git a/fs/ext4/super.c b/fs/ext4/super.c
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index a1fed66..13a33c3 100644
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--- a/fs/ext4/super.c
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+++ b/fs/ext4/super.c
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@@ -3905,6 +3905,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
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(EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb)));
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db_count = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) /
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EXT4_DESC_PER_BLOCK(sb);
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+ if (EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG)) {
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+ if (le32_to_cpu(es->s_first_meta_bg) >= db_count) {
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+ ext4_msg(sb, KERN_WARNING,
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+ "first meta block group too large: %u "
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+ "(group descriptor block count %u)",
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+ le32_to_cpu(es->s_first_meta_bg), db_count);
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+ goto failed_mount;
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+ }
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+ }
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sbi->s_group_desc = ext4_kvmalloc(db_count *
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sizeof(struct buffer_head *),
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GFP_KERNEL);
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--
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cgit v1.1
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