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Mon, 01 Jun 2026 21:18:02 -0700 (PDT) From: Pavitra Jha To: idryomov@gmail.com Cc: Slava.Dubeyko@ibm.com, amarkuze@redhat.com, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Pavitra Jha Subject: [PATCH v3] ceph: fix two unsafe bare decodes in decode_lockers() Date: Tue, 2 Jun 2026 00:17:35 -0400 Message-ID: <20260602041735.1023057-1-jhapavitra98@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <202605310022.LGyGb8eD-lkp@intel.com> References: <202605310022.LGyGb8eD-lkp@intel.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit decode_lockers() in cls_lock_client.c contains two bare decode operations that allow a malicious or compromised OSD to trigger slab-out-of-bounds reads: 1. ceph_decode_32(p) at the num_lockers field has no preceding bounds check. ceph_start_decoding() accepts struct_len=0 as valid -- the internal ceph_decode_need(p, end, 0, bad) always passes -- so when an OSD sends struct_len=0, ceph_start_decoding() returns success with p == end. The immediately following bare ceph_decode_32(p) then reads 4 bytes past the validated buffer boundary. The garbage value is passed directly to kzalloc_objs() as the locker count. The sibling function decode_watchers() in osd_client.c already uses ceph_decode_32_safe() after its own ceph_start_decoding() call. decode_lockers() was the only site using the bare variant. 2. ceph_decode_8(p) after the decode_locker() loop has no preceding bounds check. If an OSD crafts num_lockers such that the loop advances p exactly to end, the subsequent bare ceph_decode_8(p) reads one byte past the validated buffer boundary. The result is passed directly into *type, which is used as a lock type discriminator by callers, giving an OSD-controlled one-byte OOB read with direct influence over the lock type field. Fix both by replacing bare operations with their safe variants: ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers, err_inval) ceph_decode_8(p) -> ceph_decode_8_safe(p, end, *type, err_free_lockers) The goto targets differ intentionally: err_inval: is a new label returning -EINVAL directly. It is used for the pre-allocation failure path where *lockers is not yet allocated and must not be passed to ceph_free_lockers(). err_free_lockers: is the existing label. It is used for the post-allocation failure path where *lockers is allocated and must be freed. ret is set to -EINVAL before ceph_decode_8_safe() so that err_free_lockers returns the correct error code on bounds violation. Without this, err_free_lockers would return a stale ret value (0 from the successful decode_locker() loop), silently swallowing the error. -EINVAL is correct for both failure paths. The data received from the OSD is structurally malformed. -ENOMEM would misrepresent the failure class to callers and to stable@ backporters triaging error paths. KASAN report for bug 1 (kernel 7.0.0-rc7, QEMU/x86_64, KASLR disabled): ================================================================== BUG: KASAN: slab-out-of-bounds in ceph_oob3_init+0x251/0xff0 [ceph_oob3_poc] Read of size 4 at addr ffff88800a29b76e by task insmod/58 CPU: 0 UID: 0 PID: 58 Comm: insmod Tainted: G O 7.0.0-rc7-g9c2abf69da83-dirty #15 PREEMPT(lazy) Tainted: [O]=OOT_MODULE Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 Call Trace: dump_stack_lvl+0x4d/0x70 print_report+0x170/0x4f3 kasan_report+0xda/0x110 ceph_oob3_init+0x251/0xff0 [ceph_oob3_poc] do_one_initcall+0x9a/0x3a0 do_init_module+0x27c/0x790 load_module+0x4a9a/0x6350 init_module_from_file+0x15c/0x180 idempotent_init_module+0x21f/0x750 __x64_sys_finit_module+0xba/0x120 do_syscall_64+0xe2/0x570 entry_SYSCALL_64_after_hwframe+0x77/0x7f Allocated by task 58: kasan_save_stack+0x30/0x50 kasan_save_track+0x14/0x30 __kasan_kmalloc+0x7f/0x90 ceph_oob3_init+0x4d/0xff0 [ceph_oob3_poc] do_one_initcall+0x9a/0x3a0 do_init_module+0x27c/0x790 load_module+0x4a9a/0x6350 init_module_from_file+0x15c/0x180 idempotent_init_module+0x21f/0x750 __x64_sys_finit_module+0xba/0x120 do_syscall_64+0xe2/0x570 entry_SYSCALL_64_after_hwframe+0x77/0x7f The buggy address belongs to the object at ffff88800a29a000 which belongs to the cache kmalloc-8k of size 8192 The buggy address is located 5998 bytes inside of allocated 6000-byte region [ffff88800a29a000, ffff88800a29b770) Memory state around the buggy address: ffff88800a29b600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff88800a29b680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffff88800a29b700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc ^ ffff88800a29b780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== num_lockers=0xccccaaaa (OOB garbage from KASAN redzone) Bug 2 (ceph_decode_8) follows from the identical precondition. A dedicated PoC is available on request. Attacker model: a malicious or compromised OSD in a multi-tenant Ceph deployment can trigger this against any kernel client that issues the lock.get_info class method (e.g. during RBD exclusive lock acquisition) without any further privileges beyond OSD session establishment. Fixes: d4ed4a530562 ("libceph: support for lock.lock_info") Cc: stable@vger.kernel.org Signed-off-by: Pavitra Jha --- v3: Combine both fixes (ceph_decode_32 and ceph_decode_8) into a single patch per Viacheslav Dubeyko's review. Set ret = -EINVAL before ceph_decode_8_safe() so err_free_lockers returns the correct error code, not stale ret (caught by Dan Carpenter / smatch). Clarify err_inval vs err_free_lockers goto selection rationale and -EINVAL justification. --- net/ceph/cls_lock_client.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/ceph/cls_lock_client.c b/net/ceph/cls_lock_client.c index c6956f1df..4e6a6d3e4 100644 --- a/net/ceph/cls_lock_client.c +++ b/net/ceph/cls_lock_client.c @@ -299,7 +299,7 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag, if (ret) return ret; - *num_lockers = ceph_decode_32(p); + ceph_decode_32_safe(p, end, *num_lockers, err_inval); *lockers = kzalloc_objs(**lockers, *num_lockers, GFP_NOIO); if (!*lockers) return -ENOMEM; @@ -310,7 +310,8 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag, goto err_free_lockers; } - *type = ceph_decode_8(p); + ret = -EINVAL; + ceph_decode_8_safe(p, end, *type, err_free_lockers); s = ceph_extract_encoded_string(p, end, NULL, GFP_NOIO); if (IS_ERR(s)) { ret = PTR_ERR(s); @@ -320,6 +321,8 @@ static int decode_lockers(void **p, void *end, u8 *type, char **tag, *tag = s; return 0; +err_inval: + return -EINVAL; err_free_lockers: ceph_free_lockers(*lockers, *num_lockers); return ret; -- 2.53.0