On Fri, Oct 18, 2024 at 9:44 AM Jeff Layton jlayton@kernel.org wrote:
On Thu, 2024-10-17 at 18:24 -0400, Olga Kornievskaia wrote:
There is a race between laundromat handling of revoked delegations and a client sending free_stateid operation. Laundromat thread finds that delegation has expired and needs to be revoked so it marks the delegation stid revoked and it puts it on a reaper list but then it unlock the state lock and the actual delegation revocation happens without the lock. Once the stid is marked revoked a racing free_stateid processing thread does the following (1) it calls list_del_init() which removes it from the reaper list and (2) frees the delegation stid structure. The laundromat thread ends up not calling the revoke_delegation() function for this particular delegation but that means it will no release the lock lease that exists on the file.
Now, a new open for this file comes in and ends up finding that lease list isn't empty and calls nfsd_breaker_owns_lease() which ends up trying to derefence a freed delegation stateid. Leading to the followint use-after-free KASAN warning:
kernel: ================================================================== kernel: BUG: KASAN: slab-use-after-free in nfsd_breaker_owns_lease+0x140/0x160 [nfsd] kernel: Read of size 8 at addr ffff0000e73cd0c8 by task nfsd/6205 kernel: kernel: CPU: 2 UID: 0 PID: 6205 Comm: nfsd Kdump: loaded Not tainted 6.11.0-rc7+ #9 kernel: Hardware name: Apple Inc. Apple Virtualization Generic Platform, BIOS 2069.0.0.0.0 08/03/2024 kernel: Call trace: kernel: dump_backtrace+0x98/0x120 kernel: show_stack+0x1c/0x30 kernel: dump_stack_lvl+0x80/0xe8 kernel: print_address_description.constprop.0+0x84/0x390 kernel: print_report+0xa4/0x268 kernel: kasan_report+0xb4/0xf8 kernel: __asan_report_load8_noabort+0x1c/0x28 kernel: nfsd_breaker_owns_lease+0x140/0x160 [nfsd] kernel: leases_conflict+0x68/0x370 kernel: __break_lease+0x204/0xc38 kernel: nfsd_open_break_lease+0x8c/0xf0 [nfsd] kernel: nfsd_file_do_acquire+0xb3c/0x11d0 [nfsd] kernel: nfsd_file_acquire_opened+0x84/0x110 [nfsd] kernel: nfs4_get_vfs_file+0x634/0x958 [nfsd] kernel: nfsd4_process_open2+0xa40/0x1a40 [nfsd] kernel: nfsd4_open+0xa08/0xe80 [nfsd] kernel: nfsd4_proc_compound+0xb8c/0x2130 [nfsd] kernel: nfsd_dispatch+0x22c/0x718 [nfsd] kernel: svc_process_common+0x8e8/0x1960 [sunrpc] kernel: svc_process+0x3d4/0x7e0 [sunrpc] kernel: svc_handle_xprt+0x828/0xe10 [sunrpc] kernel: svc_recv+0x2cc/0x6a8 [sunrpc] kernel: nfsd+0x270/0x400 [nfsd] kernel: kthread+0x288/0x310 kernel: ret_from_fork+0x10/0x20
This patch proposes a fix that's based on adding 2 new additional stid's sc_status values that help coordinate between the laundromat and other operations (nfsd4_free_stateid() and nfsd4_delegreturn()).
First to make sure, that once the stid is marked revoked, it is not removed by the nfsd4_free_stateid(), the laundromat take a reference on the stateid. Then, coordinating whether the stid has been put on the cl_revoked list or we are processing FREE_STATEID and need to make sure to remove it from the list, each check that state and act accordingly. If laundromat has added to the cl_revoke list before the arrival of FREE_STATEID, then nfsd4_free_stateid() knows to remove it from the list. If nfsd4_free_stateid() finds that operations arrived before laundromat has placed it on cl_revoke list, it marks the state freed and then laundromat will no longer add it to the list.
Also, for nfsd4_delegreturn() when looking for the specified stid, we need to access stid that are marked removed or freeable, it means the laundromat has started processing it but hasn't finished and this delegreturn needs to return nfserr_deleg_revoked and not nfserr_bad_stateid. The latter will not trigger a FREE_STATEID and the lack of it will leave this stid on the cl_revoked list indefinitely.
Fixes: 2d4a532d385f ("nfsd: ensure that clp->cl_revoked list is protected by clp->cl_lock") CC: stable@vger.kernel.org Signed-off-by: Olga Kornievskaia okorniev@redhat.com
fs/nfsd/nfs4state.c | 15 ++++++++++++--- fs/nfsd/state.h | 2 ++ 2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index ac1859c7cc9d..cb989802e896 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -1370,10 +1370,16 @@ static void revoke_delegation(struct nfs4_delegation *dp) if (dp->dl_stid.sc_status & (SC_STATUS_REVOKED | SC_STATUS_ADMIN_REVOKED)) {
Now that I look, we'll never call revoke_delegation() without one of these bits set. Maybe we should turn that if statement into a WARN_ON_ONCE check, and then just do the rest unconditionally.
spin_lock(&clp->cl_lock);
refcount_inc(&dp->dl_stid.sc_count);If you're going to remove this, then I think you also need to add a recount_inc() to nfs4_revoke_states() before the call to revoke_delegation().
if (dp->dl_stid.sc_status & SC_STATUS_FREED) {list_del_init(&dp->dl_recall_lru);spin_unlock(&clp->cl_lock);goto out;}The FREEABLE/FREED dance is pretty complex. It'd be nice to have some documentation around it. Maybe consider adding a kerneldoc header over this function that explains that, and the requirement that you need to take an extra reference to the stateid before calling this.
list_add(&dp->dl_recall_lru, &clp->cl_revoked);
dp->dl_stid.sc_status |= SC_STATUS_FREEABLE; spin_unlock(&clp->cl_lock); }+out:
I'd just move the spin_unlock to here and get rid of the two above.
destroy_unhashed_deleg(dp);}
@@ -6545,6 +6551,7 @@ nfs4_laundromat(struct nfsd_net *nn) dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru); if (!state_expired(<, dp->dl_time)) break;
refcount_inc(&dp->dl_stid.sc_count); unhash_delegation_locked(dp, SC_STATUS_REVOKED); list_add(&dp->dl_recall_lru, &reaplist); }@@ -7156,7 +7163,9 @@ nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, if (s->sc_status & SC_STATUS_REVOKED) { spin_unlock(&s->sc_lock); dp = delegstateid(s);
list_del_init(&dp->dl_recall_lru);
if (s->sc_status & SC_STATUS_FREEABLE)list_del_init(&dp->dl_recall_lru);s->sc_status |= SC_STATUS_FREED; spin_unlock(&cl->cl_lock); nfs4_put_stid(s); ret = nfs_ok;@@ -7486,7 +7495,7 @@ nfsd4_delegreturn(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, if ((status = fh_verify(rqstp, &cstate->current_fh, S_IFREG, 0))) return status;
status = nfsd4_lookup_stateid(cstate, stateid, SC_TYPE_DELEG, 0, &s, nn);
status = nfsd4_lookup_stateid(cstate, stateid, SC_TYPE_DELEG, SC_STATUS_REVOKED|SC_STATUS_FREEABLE, &s, nn); if (status) goto out; dp = delegstateid(s);diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h index 79c743c01a47..35b3564c065f 100644 --- a/fs/nfsd/state.h +++ b/fs/nfsd/state.h @@ -114,6 +114,8 @@ struct nfs4_stid { /* For a deleg stateid kept around only to process free_stateid's: */ #define SC_STATUS_REVOKED BIT(1) #define SC_STATUS_ADMIN_REVOKED BIT(2) +#define SC_STATUS_FREEABLE BIT(3) +#define SC_STATUS_FREED BIT(4) unsigned short sc_status;
struct list_head sc_cp_list;Other than the problems above, this looks reasonable. Nice work!
Thank you for the comments Jeff! I'll address them all in v3.
-- Jeff Layton jlayton@kernel.org