ncludes kfree(prealloc)) is never reached. In btrfs_ioctl_qgroup_assign(), the code pattern is: prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL); ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst, prealloc); prealloc = NULL; // Always set to NULL regardless of return value ... kfree(prealloc); // This becomes kfree(NULL), does nothing When the level check fails, 'prealloc' is never freed by either the callee or the caller, resulting in a 64-byte memory leak per failed operation. This can be triggered repeatedly by an unprivileged user with access to a writable btrfs mount, potentially exhausting kernel memory. Fix this by freeing prealloc before the early return, ensuring prealloc is always freed on all error paths. Fixes: 8465ecec9611 ("btrfs: Check qgroup level in kernel qgroup assign.") Cc: stable@vger.kernel.org # v4.0+ Signed-off-by: Shardul Bankar --- v2: - Free prealloc directly before returning -EINVAL (no mutex held), per review from Qu Wenruo. - Drop goto-based cleanup. fs/btrfs/qgroup.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 1175b8192cd7..31ad8580322a 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1539,8 +1539,10 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst ASSERT(prealloc); /* Check the level of src and dst first */ - if (btrfs_qgroup_level(src) >= btrfs_qgroup_level(dst)) + if (btrfs_qgroup_level(src) >= btrfs_qgroup_level(dst)) { + kfree(prealloc); return -EINVAL; + } mutex_lock(&fs_info->qgroup_ioctl_lock); if (!fs_info->quota_root) { -- 2.34.1[PATCH v2 fs/btrfs v2] btrfs: fix memory leak of qgroup_list in btrfs_add_qgroup_relationShardul Bankar undefinedlinux-btrfs@vger.kernel.org undefined undefined undefined undefined undefinedƒ