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Commit 503358ae authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

ext4: avoid divide by zero when trying to mount a corrupted file system 

If s_log_groups_per_flex is greater than 31, then groups_per_flex will
will overflow and cause a divide by zero error.  This can cause kernel
BUG if such a file system is mounted.

Thanks to Nageswara R Sastry for analyzing the failure and providing
an initial patch.

http://bugzilla.kernel.org/show_bug.cgi?id=14287



Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org
parent 2de770a4

fs/ext4/super.c

+4 −4
Original line number Diff line number Diff line
@@ -1673,14 +1673,14 @@ static int ext4_fill_flex_info(struct super_block *sb) 
	size_t size;

	int i;



	if (!sbi->s_es->s_log_groups_per_flex) {

	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;

	groups_per_flex = 1 << sbi->s_log_groups_per_flex;



	if (groups_per_flex < 2) {

		sbi->s_log_groups_per_flex = 0;

		return 1;

	}



	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;

	groups_per_flex = 1 << sbi->s_log_groups_per_flex;



	/* We allocate both existing and potentially added groups */

	flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) +

			((le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) + 1) <<