From: Dan Carpenter dan.carpenter@oracle.com
commit 37b0b6b8b99c0e1c1f11abbe7cf49b6d03795b3f upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/super.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1989,7 +1989,7 @@ int ext4_alloc_flex_bg_array(struct supe { 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; @@ -2010,8 +2010,8 @@ int ext4_alloc_flex_bg_array(struct supe 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);