This is a note to let you know that I've just added the patch titled
bpf: Fix race between btf_put and btf_idr walk.
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-race-between-btf_put-and-btf_idr-walk.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f479c1f5990f0e8cb7532a9d7e9da7fa324190a2
Author: Alexei Starovoitov <ast@xxxxxxxxxx>
Date: Thu Apr 20 18:49:01 2023 -0700
bpf: Fix race between btf_put and btf_idr walk.
[ Upstream commit acf1c3d68e9a31f10d92bc67ad4673cdae5e8d92 ]
Florian and Eduard reported hard dead lock:
[ 58.433327] _raw_spin_lock_irqsave+0x40/0x50
[ 58.433334] btf_put+0x43/0x90
[ 58.433338] bpf_find_btf_id+0x157/0x240
[ 58.433353] btf_parse_fields+0x921/0x11c0
This happens since btf->refcount can be 1 at the time of btf_put() and
btf_put() will call btf_free_id() which will try to grab btf_idr_lock
and will dead lock.
Avoid the issue by doing btf_put() without locking.
Fixes: 3d78417b60fb ("bpf: Add bpf_btf_find_by_name_kind() helper.")
Fixes: 1e89106da253 ("bpf: Add bpf_core_add_cands() and wire it into bpf_core_apply_relo_insn().")
Reported-by: Florian Westphal <fw@xxxxxxxxx>
Reported-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Tested-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20230421014901.70908-1-alexei.starovoitov@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index a83a3f2745561..a8838a32f750e 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -572,8 +572,8 @@ static s32 bpf_find_btf_id(const char *name, u32 kind, struct btf **btf_p)
*btf_p = btf;
return ret;
}
- spin_lock_bh(&btf_idr_lock);
btf_put(btf);
+ spin_lock_bh(&btf_idr_lock);
}
spin_unlock_bh(&btf_idr_lock);
return ret;
@@ -7957,12 +7957,10 @@ bpf_core_find_cands(struct bpf_core_ctx *ctx, u32 local_type_id)
btf_get(mod_btf);
spin_unlock_bh(&btf_idr_lock);
cands = bpf_core_add_cands(cands, mod_btf, btf_nr_types(main_btf));
- if (IS_ERR(cands)) {
- btf_put(mod_btf);
+ btf_put(mod_btf);
+ if (IS_ERR(cands))
return ERR_CAST(cands);
- }
spin_lock_bh(&btf_idr_lock);
- btf_put(mod_btf);
}
spin_unlock_bh(&btf_idr_lock);
/* cands is a pointer to kmalloced memory here if cands->cnt > 0
