FAILED: patch "[PATCH] btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 973e57c726c1f8e77259d1c8e519519f1e9aea77
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026051218-budding-fidelity-6094@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 973e57c726c1f8e77259d1c8e519519f1e9aea77 Mon Sep 17 00:00:00 2001
From: Yochai Eisenrich <[email protected]>
Date: Sun, 22 Mar 2026 08:39:35 +0200
Subject: [PATCH] btrfs: fix btrfs_ioctl_space_info() slot_count TOCTOU which
can lead to info-leak

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.

index a4d715bbed57..b2e447f5005c 100644
@@ -2897,7 +2897,7 @@ 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;

@@ -2953,7 +2953,8 @@ 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)))
 		return -EFAULT;
 
 out:

From: Yochai Eisenrich <[email protected]>

[ 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.

---
 fs/btrfs/ioctl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index 4723013995f5b..d17d1eff8eff4 100644
@@ -3087,7 +3087,7 @@ 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;

@@ -3143,7 +3143,8 @@ 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);

2.53.0