linux-ext4 - [PATCH] mke2fs: fix check for absurdly large devices

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Message-Id: <1556227470-47076-1-git-send-email-adilger@dilger.ca>
Date:   Thu, 25 Apr 2019 23:24:30 +0200
From:   Andreas Dilger <adilger@...ger.ca>
To:     tytso@....edu
Cc:     linux-ext4@...r.kernel.org, Andreas Dilger <adilger@...ger.ca>
Subject: [PATCH] mke2fs: fix check for absurdly large devices

The check in mke2fs is intended to be for the number of blocks in the
filesystem exceeding the maximum number of addressable blocks in 2^32
bitmaps, which is (2^32 * 8 bits/byte * blocksize) = 2^47 blocks,
or 2^59 bytes = 512PiB for the common 4KiB blocksize.

However, s_log_blocksize holds log2(blocksize_in_kb), so the current
calculation is a factor of 2^10 too small.  This caused mke2fs to fail
while trying to format a 900TB filesystem.

Fixes: 101ef2e93c25 ("mke2fs: Avoid crashes / infinite loops for absurdly large devices")
Signed-off-by: Andreas Dilger <adilger@...ger.ca>
---
 misc/mke2fs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index be3586c..23e313c 100644
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -2190,9 +2190,11 @@ profile_error:
 	}
 	/*
 	 * Guard against group descriptor count overflowing... Mostly to avoid
-	 * strange results for absurdly large devices.
+	 * strange results for absurdly large devices.  This is in log2:
+	 * (blocksize) * (bits per byte) * (maximum number of block groups)
 	 */
-	if (fs_blocks_count > ((1ULL << (fs_param.s_log_block_size + 3 + 32)) - 1)) {
+	if (fs_blocks_count >
+	    (1ULL << (EXT2_BLOCK_SIZE_BITS(&fs_param) + 3 + 32)) - 1) {
 		fprintf(stderr, _("%s: Size of device (0x%llx blocks) %s "
 				  "too big to create\n\t"
 				  "a filesystem using a blocksize of %d.\n"),
-- 
1.8.0