Commit 37b0b6b8 authored Feb 28, 2020 by Dan Carpenter Committed by Theodore Ts'o Feb 29, 2020

ext4: potential crash on allocation error in ext4_alloc_flex_bg_array()



If sbi->s_flex_groups_allocated is zero and the first allocation fails
then this code will crash.  The problem is that "i--" will set "i" to
-1 but when we compare "i >= sbi->s_flex_groups_allocated" then the -1
is type promoted to unsigned and becomes UINT_MAX.  Since UINT_MAX
is more than zero, the condition is true so we call kvfree(new_groups[-1]).
The loop will carry on freeing invalid memory until it crashes.

Fixes: 7c990728 ("ext4: fix potential race between s_flex_groups online resizing and access")
Reviewed-by: Suraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20200228092142.7irbc44yaz3by7nb@kili.mountain


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

parent 6c5d9112

fs/ext4/super.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -2391,7 +2391,7 @@ int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
		{
		struct ext4_sb_info *sbi = EXT4_SB(sb);
		struct flex_groups old_groups, new_groups;
		int size, i;
		int size, i, j;

		if (!sbi->s_log_groups_per_flex)
		return 0;
		@@ -2412,8 +2412,8 @@ int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
		sizeof(struct flex_groups)),
		GFP_KERNEL);
		if (!new_groups[i]) {
		for (i--; i >= sbi->s_flex_groups_allocated; i--)
		kvfree(new_groups[i]);
		for (j = sbi->s_flex_groups_allocated; j < i; j++)
		kvfree(new_groups[j]);
		kvfree(new_groups);
		ext4_msg(sb, KERN_ERR,
		"not enough memory for %d flex groups", size);

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