From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-52961: ceph: fix BUG_ON in __ceph_build_xattrs_blob() due to stale blob size
Date: Wed, 24 Jun 2026 17:29:45 +0100 [thread overview]
Message-ID: <2026062436-CVE-2026-52961-c768@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
ceph: fix BUG_ON in __ceph_build_xattrs_blob() due to stale blob size
The generic/642 test-case can reproduce the kernel crash:
[40243.605254] ------------[ cut here ]------------
[40243.605956] kernel BUG at fs/ceph/xattr.c:918!
[40243.607142] Oops: invalid opcode: 0000 [#1] SMP PTI
[40243.608067] CPU: 7 UID: 0 PID: 498762 Comm: kworker/7:1 Not tainted 7.0.0-rc7+ #3 PREEMPT(full)
[40243.609700] Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[40243.611820] Workqueue: ceph-msgr ceph_con_workfn
[40243.612715] RIP: 0010:__ceph_build_xattrs_blob+0x1b8/0x1e0
[40243.613731] Code: 0f 84 82 fe ff ff e9 cf 8e 56 ff 48 8d 65 e8 31 c0 5b 41 5c 41 5d 5d 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 c3 cc cc cc cc <0f> 0b 4c 8b 62 08 41 8b 85 24 07 00 00 49 83 c4 04 41 89 44 24 fc
[40243.616888] RSP: 0018:ffffcc80c4d4b688 EFLAGS: 00010287
[40243.617773] RAX: 0000000000010026 RBX: 0000000000000001 RCX: 0000000000000000
[40243.618928] RDX: ffff8a773798dee0 RSI: 0000000000000000 RDI: 0000000000000000
[40243.620158] RBP: ffffcc80c4d4b6a0 R08: 0000000000000000 R09: 0000000000000000
[40243.621573] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8a75f3b58000
[40243.622907] R13: ffff8a75f3b58000 R14: 0000000000000080 R15: 000000000000bffd
[40243.624054] FS: 0000000000000000(0000) GS:ffff8a787d1b4000(0000) knlGS:0000000000000000
[40243.625331] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[40243.626269] CR2: 000072f390b623c0 CR3: 000000011c02a003 CR4: 0000000000372ef0
[40243.627408] Call Trace:
[40243.627839] <TASK>
[40243.628188] __prep_cap+0x3fd/0x4a0
[40243.628789] ? do_raw_spin_unlock+0x4e/0xe0
[40243.629474] ceph_check_caps+0x46a/0xc80
[40243.630094] ? __lock_acquire+0x4a2/0x2650
[40243.630773] ? find_held_lock+0x31/0x90
[40243.631347] ? handle_cap_grant+0x79f/0x1060
[40243.632068] ? lock_release+0xd9/0x300
[40243.632696] ? __mutex_unlock_slowpath+0x3e/0x340
[40243.633429] ? lock_release+0xd9/0x300
[40243.634052] handle_cap_grant+0xcf6/0x1060
[40243.634745] ceph_handle_caps+0x122b/0x2110
[40243.635415] mds_dispatch+0x5bd/0x2160
[40243.636034] ? ceph_con_process_message+0x65/0x190
[40243.636828] ? lock_release+0xd9/0x300
[40243.637431] ceph_con_process_message+0x7a/0x190
[40243.638184] ? kfree+0x311/0x4f0
[40243.638749] ? kfree+0x311/0x4f0
[40243.639268] process_message+0x16/0x1a0
[40243.639915] ? sg_free_table+0x39/0x90
[40243.640572] ceph_con_v2_try_read+0xf58/0x2120
[40243.641255] ? lock_acquire+0xc8/0x300
[40243.641863] ceph_con_workfn+0x151/0x820
[40243.642493] process_one_work+0x22f/0x630
[40243.643093] ? process_one_work+0x254/0x630
[40243.643770] worker_thread+0x1e2/0x400
[40243.644332] ? __pfx_worker_thread+0x10/0x10
[40243.645020] kthread+0x109/0x140
[40243.645560] ? __pfx_kthread+0x10/0x10
[40243.646125] ret_from_fork+0x3f8/0x480
[40243.646752] ? __pfx_kthread+0x10/0x10
[40243.647316] ? __pfx_kthread+0x10/0x10
[40243.647919] ret_from_fork_asm+0x1a/0x30
[40243.648556] </TASK>
[40243.648902] Modules linked in: overlay hctr2 libpolyval chacha libchacha adiantum libnh libpoly1305 essiv intel_rapl_msr intel_rapl_common intel_uncore_frequency_common skx_edac_common nfit kvm_intel kvm irqbypass joydev ghash_clmulni_intel aesni_intel rapl input_leds mac_hid psmouse vga16fb serio_raw vgastate floppy i2c_piix4 pata_acpi bochs qemu_fw_cfg i2c_smbus sch_fq_codel rbd dm_crypt msr parport_pc ppdev lp parport efi_pstore
[40243.654766] ---[ end trace 0000000000000000 ]---
Commit d93231a6bc8a ("ceph: prevent a client from exceeding the MDS
maximum xattr size") moved the required_blob_size computation to before
the __build_xattrs() call, introducing a race.
__build_xattrs() releases and reacquires i_ceph_lock during execution.
In that window, handle_cap_grant() may update i_xattrs.blob with a
newer MDS-provided blob and bump i_xattrs.version. When
__build_xattrs() detects that index_version < version, it destroys and
rebuilds the entire xattr rb-tree from the new blob, potentially
increasing count, names_size, and vals_size.
The prealloc_blob size check that follows still uses the stale
required_blob_size computed before the rebuild, so it passes even when
prealloc_blob is too small for the now-larger tree. After __set_xattr()
adds one more xattr on top, __ceph_build_xattrs_blob() is called from
the cap flush path and hits:
BUG_ON(need > ci->i_xattrs.prealloc_blob->alloc_len);
Fix this by recomputing required_blob_size after __build_xattrs()
returns, using the current tree state. Also re-validate against
m_max_xattr_size to fall back to the sync path if the rebuilt tree now
exceeds the MDS limit.
The Linux kernel CVE team has assigned CVE-2026-52961 to this issue.
Affected and fixed versions
===========================
Issue introduced in 6.0 with commit d93231a6bc8a452323d5fef16cca7107ce483a27 and fixed in 6.12.91 with commit 7eb72425c4e3234926502eb262f9d6193ccd572c
Issue introduced in 6.0 with commit d93231a6bc8a452323d5fef16cca7107ce483a27 and fixed in 6.18.33 with commit d5bd8b4e39cfa8b087448adcd48088065cd629d5
Issue introduced in 6.0 with commit d93231a6bc8a452323d5fef16cca7107ce483a27 and fixed in 7.0.10 with commit 368d21ae9081c93497b1c8163bed3eddcb2443ff
Issue introduced in 6.0 with commit d93231a6bc8a452323d5fef16cca7107ce483a27 and fixed in 7.1 with commit 0c22d9511cbde746622f8e4c11aaa63fe76d45f9
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2026-52961
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
fs/ceph/xattr.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/7eb72425c4e3234926502eb262f9d6193ccd572c
https://git.kernel.org/stable/c/d5bd8b4e39cfa8b087448adcd48088065cd629d5
https://git.kernel.org/stable/c/368d21ae9081c93497b1c8163bed3eddcb2443ff
https://git.kernel.org/stable/c/0c22d9511cbde746622f8e4c11aaa63fe76d45f9
reply other threads:[~2026-06-24 16:32 UTC|newest]
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