From 2126fb4bf3672c0dcbbf9f36cd6881e2a7a1230c Mon Sep 17 00:00:00 2001 From: Yochai Eisenrich Date: Fri, 15 May 2026 11:07:04 -0400 Subject: [PATCH] btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which can lead to info-leak [ Upstream commit 973e57c726c1f8e77259d1c8e519519f1e9aea77 ] btrfs_ioctl_space_info() has a TOCTOU race between two passes over the block group RAID type lists. The first pass counts entries to determine the allocation size, then the second pass fills the buffer. The groups_sem rwlock is released between passes, allowing concurrent block group removal to reduce the entry count. When the second pass fills fewer entries than the first pass counted, copy_to_user() copies the full alloc_size bytes including trailing uninitialized kmalloc bytes to userspace. Fix by copying only total_spaces entries (the actually-filled count from the second pass) instead of alloc_size bytes, and switch to kzalloc so any future copy size mismatch cannot leak heap data. Fixes: 7fde62bffb57 ("Btrfs: buffer results in the space_info ioctl") CC: stable@vger.kernel.org # 3.0 Signed-off-by: Yochai Eisenrich Reviewed-by: David Sterba Signed-off-by: David Sterba [ adapted upstream's `return -EFAULT;` to stable's `ret = -EFAULT;` fall-through to existing `out:` cleanup label ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ulrich Hecht --- fs/btrfs/ioctl.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 2ebcb33966bb..2606b3029e1b 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -4603,7 +4603,7 @@ static long btrfs_ioctl_space_info(struct btrfs_fs_info *fs_info, return -ENOMEM; space_args.total_spaces = 0; - dest = kmalloc(alloc_size, GFP_KERNEL); + dest = kzalloc(alloc_size, GFP_KERNEL); if (!dest) return -ENOMEM; dest_orig = dest; @@ -4662,7 +4662,8 @@ static long btrfs_ioctl_space_info(struct btrfs_fs_info *fs_info, user_dest = (struct btrfs_ioctl_space_info __user *) (arg + sizeof(struct btrfs_ioctl_space_args)); - if (copy_to_user(user_dest, dest_orig, alloc_size)) + if (copy_to_user(user_dest, dest_orig, + space_args.total_spaces * sizeof(*dest_orig))) ret = -EFAULT; kfree(dest_orig);