From: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com> mainline inclusion from mainline-v7.1-rc4 commit 0c22d9511cbde746622f8e4c11aaa63fe76d45f9 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15663 CVE: CVE-2026-52961 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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. Cc: stable@vger.kernel.org Fixes: d93231a6bc8a ("ceph: prevent a client from exceeding the MDS maximum xattr size") Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com> Reviewed-by: Alex Markuze <amarkuze@redhat.com> Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Conflicts: fs/ceph/xattr.c [Use dout to print log instead of doutc due to unmerged commit 38d46409c463 ("ceph: print cluster fsid and client global_id in all debug logs")] Signed-off-by: Pan Taixi <pantaixi1@huawei.com> --- fs/ceph/xattr.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c index 6fd6a652499e..3920aa4e40a8 100644 --- a/fs/ceph/xattr.c +++ b/fs/ceph/xattr.c @@ -1238,10 +1238,26 @@ int __ceph_setxattr(struct inode *inode, const char *name, dout("setxattr %p name '%s' issued %s\n", inode, name, ceph_cap_string(issued)); __build_xattrs(inode); + /* + * __build_xattrs() may have released and reacquired i_ceph_lock, + * during which handle_cap_grant() could have replaced i_xattrs.blob + * with a newer MDS-provided blob and bumped i_xattrs.version. If that + * caused __build_xattrs() to rebuild the rb-tree from the new blob, + * count/names_size/vals_size may now be larger than when + * required_blob_size was computed above. Recompute it here so the + * prealloc_blob size check below reflects the current tree state. + */ + required_blob_size = __get_required_blob_size(ci, name_len, val_len); + if (required_blob_size > mdsc->mdsmap->m_max_xattr_size) { + dout("%s sync (size too large): %d > %llu\n", __func__, + required_blob_size, mdsc->mdsmap->m_max_xattr_size); + goto do_sync; + } + if (!ci->i_xattrs.prealloc_blob || required_blob_size > ci->i_xattrs.prealloc_blob->alloc_len) { struct ceph_buffer *blob; spin_unlock(&ci->i_ceph_lock); -- 2.34.1