From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D1F693A4F46; Tue, 17 Mar 2026 17:03:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773766987; cv=none; b=Rw2v8N9nIdUuQoh+ziTw8lf0ZUd74C0+JBythYGIsUWOwk/XN26pTDg01ajEqUEE6JUMd3uy31DQ0jH3aHC722x3VkGkWNFNcV8ncyyvdDZ3nnIn6qU5nhO/V8aAMpw2iTgahVr3uVhAxn3rhms8cF5qPfg/E8cg6fKfERHFZ2I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773766987; c=relaxed/simple; bh=l/4hA7vBgPxZiNK987BhPsasDJJ3A+FrynTNj0BaCgM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tlSqOizCMh2C9+Z8x0n4GwUG4DpeBW1UBdS2daucDBZECPUm6Q8XCD0u318NB3JGhVCZed4kvKvf5iD80GApzxDcfDL2e4Bv1v++T1Q5rEZnnQQGZ8Y3guXZ0rp1loDvB/4fnLyQ8TzlMdr0vS/ygF1Nc/zcZA4RlJd74aqLvrw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=pLUyUtMk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="pLUyUtMk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 520EAC4CEF7; Tue, 17 Mar 2026 17:03:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773766987; bh=l/4hA7vBgPxZiNK987BhPsasDJJ3A+FrynTNj0BaCgM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pLUyUtMkLOjSXlsdRjxW2XeIOoLz5yjoc1CacDaiYdPvAVKBshW6mV3jwqUeiWXpO 4muFkVVUgPNaNARoVJ0WVnYQkj4o1+LpbuFwOCA1irt2jUQrBvM1oKeRo8uk4F3QIU dYlBNXqZrCJoHVd7+v3NeHFDN28/s0PIF75eSS0g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Boris Burkov , Qu Wenruo , Filipe Manana , David Sterba Subject: [PATCH 6.19 341/378] btrfs: fix transaction abort when snapshotting received subvolumes Date: Tue, 17 Mar 2026 17:34:58 +0100 Message-ID: <20260317163019.534485373@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260317163006.959177102@linuxfoundation.org> References: <20260317163006.959177102@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Filipe Manana commit e1b18b959025e6b5dbad668f391f65d34b39595a upstream. Currently a user can trigger a transaction abort by snapshotting a previously received snapshot a bunch of times until we reach a BTRFS_UUID_KEY_RECEIVED_SUBVOL item overflow (the maximum item size we can store in a leaf). This is very likely not common in practice, but if it happens, it turns the filesystem into RO mode. The snapshot, send and set_received_subvol and subvol_setflags (used by receive) don't require CAP_SYS_ADMIN, just inode_owner_or_capable(). A malicious user could use this to turn a filesystem into RO mode and disrupt a system. Reproducer script: $ cat test.sh #!/bin/bash DEV=/dev/sdi MNT=/mnt/sdi # Use smallest node size to make the test faster. mkfs.btrfs -f --nodesize 4K $DEV mount $DEV $MNT # Create a subvolume and set it to RO so that it can be used for send. btrfs subvolume create $MNT/sv touch $MNT/sv/foo btrfs property set $MNT/sv ro true # Send and receive the subvolume into snaps/sv. mkdir $MNT/snaps btrfs send $MNT/sv | btrfs receive $MNT/snaps # Now snapshot the received subvolume, which has a received_uuid, a # lot of times to trigger the leaf overflow. total=500 for ((i = 1; i <= $total; i++)); do echo -ne "\rCreating snapshot $i/$total" btrfs subvolume snapshot -r $MNT/snaps/sv $MNT/snaps/sv_$i > /dev/null done echo umount $MNT When running the test: $ ./test.sh (...) Create subvolume '/mnt/sdi/sv' At subvol /mnt/sdi/sv At subvol sv Creating snapshot 496/500ERROR: Could not create subvolume: Value too large for defined data type Creating snapshot 497/500ERROR: Could not create subvolume: Read-only file system Creating snapshot 498/500ERROR: Could not create subvolume: Read-only file system Creating snapshot 499/500ERROR: Could not create subvolume: Read-only file system Creating snapshot 500/500ERROR: Could not create subvolume: Read-only file system And in dmesg/syslog: $ dmesg (...) [251067.627338] BTRFS warning (device sdi): insert uuid item failed -75 (0x4628b21c4ac8d898, 0x2598bee2b1515c91) type 252! [251067.629212] ------------[ cut here ]------------ [251067.630033] BTRFS: Transaction aborted (error -75) [251067.630871] WARNING: fs/btrfs/transaction.c:1907 at create_pending_snapshot.cold+0x52/0x465 [btrfs], CPU#10: btrfs/615235 [251067.632851] Modules linked in: btrfs dm_zero (...) [251067.644071] CPU: 10 UID: 0 PID: 615235 Comm: btrfs Tainted: G W 6.19.0-rc8-btrfs-next-225+ #1 PREEMPT(full) [251067.646165] Tainted: [W]=WARN [251067.646733] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [251067.648735] RIP: 0010:create_pending_snapshot.cold+0x55/0x465 [btrfs] [251067.649984] Code: f0 48 0f (...) [251067.653313] RSP: 0018:ffffce644908fae8 EFLAGS: 00010292 [251067.653987] RAX: 00000000ffffff01 RBX: ffff8e5639e63a80 RCX: 00000000ffffffd3 [251067.655042] RDX: ffff8e53faa76b00 RSI: 00000000ffffffb5 RDI: ffffffffc0919750 [251067.656077] RBP: ffffce644908fbd8 R08: 0000000000000000 R09: ffffce644908f820 [251067.657068] R10: ffff8e5adc1fffa8 R11: 0000000000000003 R12: ffff8e53c0431bd0 [251067.658050] R13: ffff8e5414593600 R14: ffff8e55efafd000 R15: 00000000ffffffb5 [251067.659019] FS: 00007f2a4944b3c0(0000) GS:ffff8e5b27dae000(0000) knlGS:0000000000000000 [251067.660115] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [251067.660943] CR2: 00007ffc5aa57898 CR3: 00000005813a2003 CR4: 0000000000370ef0 [251067.661972] Call Trace: [251067.662292] [251067.662653] create_pending_snapshots+0x97/0xc0 [btrfs] [251067.663413] btrfs_commit_transaction+0x26e/0xc00 [btrfs] [251067.664257] ? btrfs_qgroup_convert_reserved_meta+0x35/0x390 [btrfs] [251067.665238] ? _raw_spin_unlock+0x15/0x30 [251067.665837] ? record_root_in_trans+0xa2/0xd0 [btrfs] [251067.666531] btrfs_mksubvol+0x330/0x580 [btrfs] [251067.667145] btrfs_mksnapshot+0x74/0xa0 [btrfs] [251067.667827] __btrfs_ioctl_snap_create+0x194/0x1d0 [btrfs] [251067.668595] btrfs_ioctl_snap_create_v2+0x107/0x130 [btrfs] [251067.669479] btrfs_ioctl+0x1580/0x2690 [btrfs] [251067.670093] ? count_memcg_events+0x6d/0x180 [251067.670849] ? handle_mm_fault+0x1a0/0x2a0 [251067.671652] __x64_sys_ioctl+0x92/0xe0 [251067.672406] do_syscall_64+0x50/0xf20 [251067.673129] entry_SYSCALL_64_after_hwframe+0x76/0x7e [251067.674096] RIP: 0033:0x7f2a495648db [251067.674812] Code: 00 48 89 (...) [251067.678227] RSP: 002b:00007ffc5aa57840 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [251067.679691] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f2a495648db [251067.681145] RDX: 00007ffc5aa588b0 RSI: 0000000050009417 RDI: 0000000000000004 [251067.682511] RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000 [251067.683842] R10: 000000000000000a R11: 0000000000000246 R12: 00007ffc5aa59910 [251067.685176] R13: 00007ffc5aa588b0 R14: 0000000000000004 R15: 0000000000000006 [251067.686524] [251067.686972] ---[ end trace 0000000000000000 ]--- [251067.687890] BTRFS: error (device sdi state A) in create_pending_snapshot:1907: errno=-75 unknown [251067.689049] BTRFS info (device sdi state EA): forced readonly [251067.689054] BTRFS warning (device sdi state EA): Skipping commit of aborted transaction. [251067.690119] BTRFS: error (device sdi state EA) in cleanup_transaction:2043: errno=-75 unknown [251067.702028] BTRFS info (device sdi state EA): last unmount of filesystem 46dc3975-30a2-4a69-a18f-418b859cccda Fix this by ignoring -EOVERFLOW errors from btrfs_uuid_tree_add() in the snapshot creation code when attempting to add the BTRFS_UUID_KEY_RECEIVED_SUBVOL item. This is OK because it's not critical and we are still able to delete the snapshot, as snapshot/subvolume deletion ignores if a BTRFS_UUID_KEY_RECEIVED_SUBVOL is missing (see inode.c:btrfs_delete_subvolume()). As for send/receive, we can still do send/receive operations since it always peeks the first root ID in the existing BTRFS_UUID_KEY_RECEIVED_SUBVOL (it could peek any since all snapshots have the same content), and even if the key is missing, it falls back to searching by BTRFS_UUID_KEY_SUBVOL key. A test case for fstests will be sent soon. Fixes: dd5f9615fc5c ("Btrfs: maintain subvolume items in the UUID tree") CC: stable@vger.kernel.org # 3.12+ Reviewed-by: Boris Burkov Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/transaction.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -1904,6 +1904,22 @@ static noinline int create_pending_snaps ret = btrfs_uuid_tree_add(trans, new_root_item->received_uuid, BTRFS_UUID_KEY_RECEIVED_SUBVOL, objectid); + /* + * We are creating of lot of snapshots of the same root that was + * received (has a received UUID) and reached a leaf's limit for + * an item. We can safely ignore this and avoid a transaction + * abort. A deletion of this snapshot will still work since we + * ignore if an item with a BTRFS_UUID_KEY_RECEIVED_SUBVOL key + * is missing (see btrfs_delete_subvolume()). Send/receive will + * work too since it peeks the first root id from the existing + * item (it could peek any), and in case it's missing it + * falls back to search by BTRFS_UUID_KEY_SUBVOL keys. + * Creation of a snapshot does not require CAP_SYS_ADMIN, so + * we don't want users triggering transaction aborts, either + * intentionally or not. + */ + if (ret == -EOVERFLOW) + ret = 0; if (unlikely(ret && ret != -EEXIST)) { btrfs_abort_transaction(trans, ret); goto fail;