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bpf: Fix race between btf_put and btf_idr walk. 

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: 3d78417b60 ("bpf: Add bpf_btf_find_by_name_kind() helper.")
Fixes: 1e89106da2 ("bpf: Add bpf_core_add_cands() and wire it into bpf_core_apply_relo_insn().")
Reported-by: Florian Westphal <fw@strlen.de>
Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20230421014901.70908-1-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2023-04-20 18:49:01 -07:00 committed by Daniel Borkmann
parent 267a6e4e78
commit acf1c3d68e
1 changed files with 4 additions and 6 deletions
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10
kernel/bpf/btf.c
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@ -577,8 +577,8 @@ 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;
@ -8354,12 +8354,10 @@ check_modules:
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);
return ERR_CAST(cands);
}
spin_lock_bh(&btf_idr_lock);
btf_put(mod_btf);
if (IS_ERR(cands))
return ERR_CAST(cands);
spin_lock_bh(&btf_idr_lock);
}
spin_unlock_bh(&btf_idr_lock);
/* cands is a pointer to kmalloced memory here if cands->cnt > 0