Re: [PATCH v3] ceph: fix multiple unsafe decodes in decode_locker()

[Ilya Dryomov]

On Fri, Aug 7, 2026 at 5:15 PM Pavitra Jha <jhapavitra98@xxxxxxxxx> wrote:
>
> Ilya,
>
> This has been Reviewed-by'd by Slava since Jun 2 (v3), no outstanding
> comments or NACKs on this one. It's been quiet for two months now.
> Any blocker to applying, or should I rebase and resend?

Hi Pavitra,

Sorry, no need to resend.  Slava forgot to add this patch to our
integration branch like he did another similar patch of yours which
is already upstream -- "libceph: fix two unsafe bare decodes in
decode_lockers()".  I'll eventually scrub the list and pick up anything
that was missed this way, at this point likely into 7.3.

Thanks,

                Ilya

>
> thanks,
> Pavitra
>
> On Tue, 2 Jun 2026 at 10:32, Pavitra Jha <jhapavitra98@xxxxxxxxx> wrote:
> >
> > decode_locker() in cls_lock_client.c contains three unsafe decode
> > operations that allow a malicious or compromised OSD to trigger
> > slab-out-of-bounds reads:
> >
> > 1. ceph_decode_copy() at the locker_id_t name field has no preceding
> >    bounds check. With p == end after ceph_start_decoding() accepts
> >    struct_len=0, this reads sizeof(ceph_entity_name) = 9 bytes past
> >    the validated buffer boundary.
> >
> > 2. *p += sizeof(struct ceph_timespec) after the locker_info_t header
> >    is an unchecked pointer advance. A malicious OSD can position p
> >    past end, causing all subsequent _safe checks to pass against a
> >    bogus boundary.
> >
> > 3. len = ceph_decode_32(p) has no preceding bounds check, and the
> >    immediately following *p += len is uncapped. A malicious OSD can
> >    send len=0xffffffff, advancing p gigabytes past end and escaping
> >    the decode window entirely.
> >
> > Fix all three by replacing bare operations with their safe variants:
> >   ceph_decode_copy   -> ceph_decode_copy_safe
> >   *p += sizeof(...)  -> ceph_decode_skip_n
> >   ceph_decode_32(p)  -> ceph_decode_32_safe
> >   *p += len          -> ceph_decode_skip_n
> >
> > A new out_bad: label is added to return -EINVAL on any bounds
> > violation. -EINVAL is appropriate here: the data received from the OSD
> > is structurally malformed, which is an invalid argument to the decode
> > contract regardless of whether the caller or the wire is at fault.
> >
> > KASAN report (kernel 7.0.0-rc7, QEMU/x86_64, KASLR disabled):
> >
> >   [   26.183969] ceph_oob4_poc: buf=ffff888009e31000 end=ffff888009e31fa0
> >   [   26.186087] ceph_oob4_poc: struct_v=1 struct_len=0 p==end: 1
> >   [   26.186738] ceph_oob4_poc: triggering bare ceph_decode_32 past slab boundary...
> >   [   26.187679] ==================================================================
> >   [   26.188236] BUG: KASAN: slab-out-of-bounds in ceph_oob4_init+0x22b/0xff0 [ceph_oob4_poc]
> >   [   26.188236] Read of size 4 at addr ffff888009e31fa0 by task insmod/59
> >   [   26.188236] CPU: 0 UID: 0 PID: 59 Comm: insmod Tainted: G           O        7.0.0-rc7-g9c2abf69da83-dirty #15 PREEMPT(lazy)
> >   [   26.188236] Tainted: [O]=OOT_MODULE
> >   [   26.188236] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
> >   [   26.188236] Call Trace:
> >   [   26.188236]  <TASK>
> >   [   26.188236]  dump_stack_lvl+0x4d/0x70
> >   [   26.188236]  print_report+0x170/0x4f3
> >   [   26.188236]  kasan_report+0xda/0x110
> >   [   26.188236]  ceph_oob4_init+0x22b/0xff0 [ceph_oob4_poc]
> >   [   26.188236]  do_one_initcall+0x9a/0x3a0
> >   [   26.188236]  do_init_module+0x27c/0x790
> >   [   26.188236]  load_module+0x4a9a/0x6350
> >   [   26.188236]  init_module_from_file+0x15c/0x180
> >   [   26.188236]  idempotent_init_module+0x21f/0x750
> >   [   26.188236]  __x64_sys_finit_module+0xba/0x120
> >   [   26.188236]  do_syscall_64+0xe2/0x570
> >   [   26.188236]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >   [   26.188236]  </TASK>
> >   [   26.188236] The buggy address belongs to the object at ffff888009e31000
> >   [   26.188236]  which belongs to the cache kmalloc-4k of size 4096
> >   [   26.188236] The buggy address is located 0 bytes to the right of
> >   [   26.188236]  allocated 4000-byte region [ffff888009e31000, ffff888009e31fa0)
> >   [   26.188236]  ffff888009e31f80: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
> >   [   26.188236]                                ^
> >   [   26.188236]  ffff888009e32000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >   [   26.188236] ==================================================================
> >   [   26.255513] ceph_oob4_poc: len=0xcccccccc (OOB garbage from KASAN redzone)
> >
> >   0xCCCCCCCC is KASAN redzone poison, confirming the read landed in
> >   the slab redzone immediately past the 4000-byte allocation.
> >
> > 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@xxxxxxxxxxxxxxx
> > Signed-off-by: Pavitra Jha <jhapavitra98@xxxxxxxxx>
> > ---
> > v3: Split ceph_decode_copy_safe call to fit 80-column limit,
> >     per Viacheslav Dubeyko's review of v2.
> > v2: Move inline comments above ceph_decode_skip_n calls, rename
> >     label bad -> out_bad, per Viacheslav Dubeyko's review.
> > ---
> >  net/ceph/cls_lock_client.c | 13 +++++++++----
> >  1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/ceph/cls_lock_client.c b/net/ceph/cls_lock_client.c
> > index 4e6a6d3e4..79a449897 100644
> > --- a/net/ceph/cls_lock_client.c
> > +++ b/net/ceph/cls_lock_client.c
> > @@ -259,7 +259,8 @@ static int decode_locker(void **p, void *end, struct ceph_locker *locker)
> >         if (ret)
> >                 return ret;
> >
> > -       ceph_decode_copy(p, &locker->id.name, sizeof(locker->id.name));
> > +       ceph_decode_copy_safe(p, end, &locker->id.name,
> > +                             sizeof(locker->id.name), out_bad);
> >         s = ceph_extract_encoded_string(p, end, NULL, GFP_NOIO);
> >         if (IS_ERR(s))
> >                 return PTR_ERR(s);
> > @@ -270,19 +271,23 @@ static int decode_locker(void **p, void *end, struct ceph_locker *locker)
> >         if (ret)
> >                 return ret;
> >
> > -       *p += sizeof(struct ceph_timespec); /* skip expiration */
> > +       /* skip expiration */
> > +       ceph_decode_skip_n(p, end, sizeof(struct ceph_timespec), out_bad);
> >
> >         ret = ceph_decode_entity_addr(p, end, &locker->info.addr);
> >         if (ret)
> >                 return ret;
> >
> > -       len = ceph_decode_32(p);
> > -       *p += len; /* skip description */
> > +       ceph_decode_32_safe(p, end, len, out_bad);
> > +       /* skip description */
> > +       ceph_decode_skip_n(p, end, len, out_bad);
> >
> >         dout("%s %s%llu cookie %s addr %s\n", __func__,
> >              ENTITY_NAME(locker->id.name), locker->id.cookie,
> >              ceph_pr_addr(&locker->info.addr));
> >         return 0;
> > +out_bad:
> > +       return -EINVAL;
> >  }
> >
> >  static int decode_lockers(void **p, void *end, u8 *type, char **tag,
> > --
> > 2.53.0
> >