6.12-stable review patch. If anyone has any objections, please let me know.
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From: Shardul Bankar shardulsb08@gmail.com
[ Upstream commit f260c6aff0b8af236084012d14f9f1bf792ea883 ]
When btrfs_add_qgroup_relation() is called with invalid qgroup levels (src >= dst), the function returns -EINVAL directly without freeing the preallocated qgroup_list structure passed by the caller. This causes a memory leak because the caller unconditionally sets the pointer to NULL after the call, preventing any cleanup.
The issue occurs because the level validation check happens before the mutex is acquired and before any error handling path that would free the prealloc pointer. On this early return, the cleanup code at the 'out' label (which includes 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: 4addc1ffd67a ("btrfs: qgroup: preallocate memory before adding a relation") Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Shardul Bankar shardulsb08@gmail.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2c9b38ae40da2..3c77f3506faf3 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1585,8 +1585,10 @@ 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) {