6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andrea Righi andrea.righi@canonical.com
commit c312828c37a72fe2d033a961c47c227b0767e9f8 upstream.
bpf_cgroup_from_id() is basically a wrapper to cgroup_get_from_id(), that is relying on kernfs to determine the right cgroup associated to the target id.
As a kfunc, it has the potential to be attached to any function through BPF, particularly in contexts where certain locks are held.
However, kernfs is not using an irq safe spinlock for kernfs_idr_lock, that means any kernfs function that is acquiring this lock can be interrupted and potentially hit bpf_cgroup_from_id() in the process, triggering a deadlock.
For example, it is really easy to trigger a lockdep splat between kernfs_idr_lock and rq->_lock, attaching a small BPF program to __set_cpus_allowed_ptr_locked() that just calls bpf_cgroup_from_id():
===================================================== WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected 6.7.0-rc7-virtme #5 Not tainted ----------------------------------------------------- repro/131 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: ffffffffb2dc4578 (kernfs_idr_lock){+.+.}-{2:2}, at: kernfs_find_and_get_node_by_id+0x1d/0x80
and this task is already holding: ffff911cbecaf218 (&rq->__lock){-.-.}-{2:2}, at: task_rq_lock+0x50/0xc0 which would create a new lock dependency: (&rq->__lock){-.-.}-{2:2} -> (kernfs_idr_lock){+.+.}-{2:2}
but this new dependency connects a HARDIRQ-irq-safe lock: (&rq->__lock){-.-.}-{2:2}
... which became HARDIRQ-irq-safe at: lock_acquire+0xbf/0x2b0 _raw_spin_lock_nested+0x2e/0x40 scheduler_tick+0x5d/0x170 update_process_times+0x9c/0xb0 tick_periodic+0x27/0xe0 tick_handle_periodic+0x24/0x70 __sysvec_apic_timer_interrupt+0x64/0x1a0 sysvec_apic_timer_interrupt+0x6f/0x80 asm_sysvec_apic_timer_interrupt+0x1a/0x20 memcpy+0xc/0x20 arch_dup_task_struct+0x15/0x30 copy_process+0x1ce/0x1eb0 kernel_clone+0xac/0x390 kernel_thread+0x6f/0xa0 kthreadd+0x199/0x230 ret_from_fork+0x31/0x50 ret_from_fork_asm+0x1b/0x30
to a HARDIRQ-irq-unsafe lock: (kernfs_idr_lock){+.+.}-{2:2}
... which became HARDIRQ-irq-unsafe at: ... lock_acquire+0xbf/0x2b0 _raw_spin_lock+0x30/0x40 __kernfs_new_node.isra.0+0x83/0x280 kernfs_create_root+0xf6/0x1d0 sysfs_init+0x1b/0x70 mnt_init+0xd9/0x2a0 vfs_caches_init+0xcf/0xe0 start_kernel+0x58a/0x6a0 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0xc5/0xe0 secondary_startup_64_no_verify+0x178/0x17b
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(kernfs_idr_lock); local_irq_disable(); lock(&rq->__lock); lock(kernfs_idr_lock); <Interrupt> lock(&rq->__lock);
*** DEADLOCK ***
Prevent this deadlock condition converting kernfs_idr_lock to a raw irq safe spinlock.
The performance impact of this change should be negligible and it also helps to prevent similar deadlock conditions with any other subsystems that may depend on kernfs.
Fixes: 332ea1f697be ("bpf: Add bpf_cgroup_from_id() kfunc") Cc: stable stable@kernel.org Signed-off-by: Andrea Righi andrea.righi@canonical.com Acked-by: Tejun Heo tj@kernel.org Link: https://lore.kernel.org/r/20231229074916.53547-1-andrea.righi@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/kernfs/dir.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-)
--- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -27,7 +27,7 @@ static DEFINE_RWLOCK(kernfs_rename_lock) */ static DEFINE_SPINLOCK(kernfs_pr_cont_lock); static char kernfs_pr_cont_buf[PATH_MAX]; /* protected by pr_cont_lock */ -static DEFINE_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */ +static DEFINE_RAW_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */
#define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
@@ -539,6 +539,7 @@ void kernfs_put(struct kernfs_node *kn) { struct kernfs_node *parent; struct kernfs_root *root; + unsigned long flags;
if (!kn || !atomic_dec_and_test(&kn->count)) return; @@ -563,9 +564,9 @@ void kernfs_put(struct kernfs_node *kn) simple_xattrs_free(&kn->iattr->xattrs, NULL); kmem_cache_free(kernfs_iattrs_cache, kn->iattr); } - spin_lock(&kernfs_idr_lock); + raw_spin_lock_irqsave(&kernfs_idr_lock, flags); idr_remove(&root->ino_idr, (u32)kernfs_ino(kn)); - spin_unlock(&kernfs_idr_lock); + raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); kmem_cache_free(kernfs_node_cache, kn);
kn = parent; @@ -607,6 +608,7 @@ static struct kernfs_node *__kernfs_new_ struct kernfs_node *kn; u32 id_highbits; int ret; + unsigned long irqflags;
name = kstrdup_const(name, GFP_KERNEL); if (!name) @@ -617,13 +619,13 @@ static struct kernfs_node *__kernfs_new_ goto err_out1;
idr_preload(GFP_KERNEL); - spin_lock(&kernfs_idr_lock); + raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags); ret = idr_alloc_cyclic(&root->ino_idr, kn, 1, 0, GFP_ATOMIC); if (ret >= 0 && ret < root->last_id_lowbits) root->id_highbits++; id_highbits = root->id_highbits; root->last_id_lowbits = ret; - spin_unlock(&kernfs_idr_lock); + raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags); idr_preload_end(); if (ret < 0) goto err_out2; @@ -659,9 +661,9 @@ static struct kernfs_node *__kernfs_new_ return kn;
err_out3: - spin_lock(&kernfs_idr_lock); + raw_spin_lock_irqsave(&kernfs_idr_lock, irqflags); idr_remove(&root->ino_idr, (u32)kernfs_ino(kn)); - spin_unlock(&kernfs_idr_lock); + raw_spin_unlock_irqrestore(&kernfs_idr_lock, irqflags); err_out2: kmem_cache_free(kernfs_node_cache, kn); err_out1: @@ -702,8 +704,9 @@ struct kernfs_node *kernfs_find_and_get_ struct kernfs_node *kn; ino_t ino = kernfs_id_ino(id); u32 gen = kernfs_id_gen(id); + unsigned long flags;
- spin_lock(&kernfs_idr_lock); + raw_spin_lock_irqsave(&kernfs_idr_lock, flags);
kn = idr_find(&root->ino_idr, (u32)ino); if (!kn) @@ -727,10 +730,10 @@ struct kernfs_node *kernfs_find_and_get_ if (unlikely(!__kernfs_active(kn) || !atomic_inc_not_zero(&kn->count))) goto err_unlock;
- spin_unlock(&kernfs_idr_lock); + raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); return kn; err_unlock: - spin_unlock(&kernfs_idr_lock); + raw_spin_unlock_irqrestore(&kernfs_idr_lock, flags); return NULL; }