diff options
authorDan Carpenter <>2020-02-28 12:22:56 +0300
committerTheodore Ts'o <>2020-02-29 17:48:08 -0500
commit37b0b6b8b99c0e1c1f11abbe7cf49b6d03795b3f (patch)
parent6c5d911249290f41f7b50b43344a7520605b1acb (diff)
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: 7c990728b99e ("ext4: fix potential race between s_flex_groups online resizing and access") Reviewed-by: Suraj Jitindar Singh <> Signed-off-by: Dan Carpenter <> Cc: Link: Signed-off-by: Theodore Ts'o <>
1 files 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)),
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]);
ext4_msg(sb, KERN_ERR,
"not enough memory for %d flex groups", size);