[PATCH] ceph: fix OOB read in ceph_osdc_list_watchers via uncapped outdata_len

[Pavitra Jha <jhapavitra98@gmail.com>]

The OSD reply header field op->payload_len is wire-controlled and is
copied directly into m->outdata_len[i] without any bounds check:

  m->outdata_len[i] = le32_to_cpu(op->payload_len);

This value propagates unchecked to req->r_ops[0].outdata_len and is
then used to set the decode boundary in ceph_osdc_list_watchers():

  void *const end = p + req->r_ops[0].outdata_len;

The actual data allocation is always exactly one page:
  ceph_alloc_page_vector(1, GFP_NOIO)
  ceph_osd_data_pages_init(..., PAGE_SIZE, ...)

The messenger caps the copy to PAGE_SIZE bytes, but the decode window
end is set from the uncapped wire value. A malicious OSD can send
outdata_len=0x10000, causing _safe decoder boundary checks to pass
while the physical reads cross the slab allocation boundary.

KASAN report (kernel 7.0.0-rc7, QEMU/x86_64, KASLR disabled):
  ==================================================================
  BUG: KASAN: slab-out-of-bounds in ceph_oob2_init+0x23d/0xff0 [ceph_oob2_poc]
  Read of size 4 at addr ffff88800a229f9e by task insmod/57

  CPU: 0 UID: 0 PID: 57 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:
   <TASK>
   dump_stack_lvl+0x4d/0x70
   print_report+0x170/0x4f3
   ? __pfx__raw_spin_lock_irqsave+0x10/0x10
   kasan_report+0xda/0x110
   ? ceph_oob2_init+0x23d/0xff0 [ceph_oob2_poc]
   ? ceph_oob2_init+0x23d/0xff0 [ceph_oob2_poc]
   ? __pfx_ceph_oob2_init+0x10/0x10 [ceph_oob2_poc]
   ceph_oob2_init+0x23d/0xff0 [ceph_oob2_poc]
   do_one_initcall+0x9a/0x3a0
   ? __pfx_do_one_initcall+0x10/0x10
   ? kasan_unpoison+0x44/0x70
   do_init_module+0x27c/0x790
   ? __pfx_do_init_module+0x10/0x10
   ? __kasan_slab_free+0x47/0x70
   ? kfree+0x15f/0x3b0
   load_module+0x4a9a/0x6350
   ? __pfx_load_module+0x10/0x10
   ? security_file_permission+0x24/0x50
   ? kernel_read_file+0x2ed/0x770
   ? init_module_from_file+0x15c/0x180
   init_module_from_file+0x15c/0x180
   ? __pfx_init_module_from_file+0x10/0x10
   ? tick_nohz_handler+0x2a3/0x640
   ? _raw_spin_lock+0x7e/0xd0
   idempotent_init_module+0x21f/0x750
   ? __pfx_idempotent_init_module+0x10/0x10
   ? fdget+0x4e/0x4a0
   ? fdget+0x4e/0x4a0
   __x64_sys_finit_module+0xba/0x120
   do_syscall_64+0xe2/0x570
   ? exc_page_fault+0x66/0xb0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

  Allocated by task 57:
   kasan_save_stack+0x30/0x50
   kasan_save_track+0x14/0x30
   __kasan_kmalloc+0x7f/0x90
   ceph_oob2_init+0x44/0xff0 [ceph_oob2_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 ffff88800a229000
   which belongs to the cache kmalloc-4k of size 4096
  The buggy address is located 3998 bytes inside of
   allocated 4000-byte region [ffff88800a229000, ffff88800a229fa0)

  Memory state around the buggy address:
   ffff88800a229e80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
   ffff88800a229f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  >ffff88800a229f80: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
                                 ^
   ffff88800a22a000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
   ffff88800a22a080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ==================================================================

  val=0xccccaaaa (OOB garbage from KASAN redzone)

Fix by capping the decode window end to PAGE_SIZE, matching the
actual allocation size.

Attacker model: a malicious or compromised OSD in a multi-tenant
Ceph deployment can trigger this against any client issuing
CEPH_OSD_OP_LIST_WATCHERS without further privileges beyond OSD
session establishment.

Fixes: a4ed38d7a180 ("libceph: support for CEPH_OSD_OP_LIST_WATCHERS")
Cc: stable@vger.kernel.org
Signed-off-by: Pavitra Jha <jhapavitra98@gmail.com>
---
 net/ceph/osd_client.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
index 0148e4c40..a67093cf4 100644
--- a/net/ceph/osd_client.c
+++ b/net/ceph/osd_client.c
@@ -5091,7 +5091,7 @@ int ceph_osdc_list_watchers(struct ceph_osd_client *osdc,
 	ret = ceph_osdc_wait_request(osdc, req);
 	if (ret >= 0) {
 		void *p = page_address(pages[0]);
-		void *const end = p + req->r_ops[0].outdata_len;
+		void *const end = p + min_t(u32, req->r_ops[0].outdata_len, PAGE_SIZE);
 
 		ret = decode_watchers(&p, end, watchers, num_watchers);
 	}
-- 
2.53.0