From 37b0b6b8b99c0e1c1f11abbe7cf49b6d03795b3f Mon Sep 17 00:00:00 2001
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Fri, 28 Feb 2020 12:22:56 +0300
Subject: [PATCH] ext4: potential crash on allocation error in
ext4_alloc_flex_bg_array()
Git-commit: 37b0b6b8b99c0e1c1f11abbe7cf49b6d03795b3f
Patch-mainline: v5.6-rc4
References: bsc#1166940
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: 7c990728b99e ("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>
Acked-by: Jan Kara <jack@suse.cz>
---
fs/ext4/super.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ff1b764b0c0e..0c7c4adb664e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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);
--
2.16.4