[PATCH] mke2fs: Avoid crashes / infinite loops for absurdly large devices

[PATCH] mke2fs: Avoid crashes / infinite loops for absurdly large devices

[Jan Kara]

When a device reports absurdly high size, some arithmetics in mke2fs can
overflow (e.g. number of block descriptors) and we end in an infinite
loop. Fix that by checking and refusing insanely large devices.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 misc/mke2fs.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index d98e71e0d706..6a83bd9fe2af 100644
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -2089,6 +2089,18 @@ profile_error:
 			EXT2_BLOCK_SIZE(&fs_param));
 		exit(1);
 	}
+	/*
+	 * Guard against group descriptor count overflowing... Mostly to avoid
+	 * strange results for absurdly large devices.
+	 */
+	if (fs_blocks_count > ((1ULL << (fs_param.s_log_block_size + 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"),
+			program_name, fs_blocks_count, device_name,
+			EXT2_BLOCK_SIZE(&fs_param));
+		exit(1);
+	}
 
 	ext2fs_blocks_count_set(&fs_param, fs_blocks_count);
 
-- 
2.6.6

Re: [PATCH] mke2fs: Avoid crashes / infinite loops for absurdly large devices

[Theodore Ts'o]

On Tue, Oct 25, 2016 at 02:11:44PM +0200, Jan Kara wrote:
> When a device reports absurdly high size, some arithmetics in mke2fs can
> overflow (e.g. number of block descriptors) and we end in an infinite
> loop. Fix that by checking and refusing insanely large devices.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Thanks, applied.

					- Ted