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When a malicious or compromised OSD sends a cls_lock_get_info_reply with struct_len=0, ceph_start_decoding() returns success with p == end, leaving zero bytes guaranteed for subsequent reads. The immediately following bare ceph_decode_32(p) in decode_lockers() has no preceding bounds check. With p == end this is a 4-byte read past the validated buffer boundary. The garbage value is then passed to kzalloc_objs() as the locker count. The sibling function decode_watchers() in osd_client.c already uses the safe variant ceph_decode_32_safe() after its own ceph_start_decoding() call. decode_lockers() is the only site using the bare variant, confirming an oversight. Fix by replacing ceph_decode_32(p) with ceph_decode_32_safe(p, end, *num_lockers, err_inval), adding a new err_inval label that returns -EINVAL directly without attempting to free an uninitialized lockers pointer. KASAN report (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) 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 --- net/ceph/cls_lock_client.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ceph/cls_lock_client.c b/net/ceph/cls_lock_client.c index c6956f1df..78276273c 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; @@ -320,6 +320,8 @@ 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