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From 8358b02bf67d3a5d8a825070e1aa73f25fb2e4c7 Mon Sep 17 00:00:00 2001
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From: Jann Horn <jannh@google.com>
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Date: Tue, 26 Apr 2016 22:26:26 +0200
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Subject: [PATCH] bpf: fix double-fdput in replace_map_fd_with_map_ptr()
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When bpf(BPF_PROG_LOAD, ...) was invoked with a BPF program whose bytecode
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references a non-map file descriptor as a map file descriptor, the error
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handling code called fdput() twice instead of once (in __bpf_map_get() and
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in replace_map_fd_with_map_ptr()). If the file descriptor table of the
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current task is shared, this causes f_count to be decremented too much,
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allowing the struct file to be freed while it is still in use
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(use-after-free). This can be exploited to gain root privileges by an
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unprivileged user.
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This bug was introduced in
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commit 0246e64d9a5f ("bpf: handle pseudo BPF_LD_IMM64 insn"), but is only
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exploitable since
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commit 1be7f75d1668 ("bpf: enable non-root eBPF programs") because
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previously, CAP_SYS_ADMIN was required to reach the vulnerable code.
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(posted publicly according to request by maintainer)
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Signed-off-by: Jann Horn <jannh@google.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Acked-by: Alexei Starovoitov <ast@kernel.org>
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Acked-by: Daniel Borkmann <daniel@iogearbox.net>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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kernel/bpf/verifier.c | 1 -
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1 file changed, 1 deletion(-)
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
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index 618ef77c302a..db2574e7b8b0 100644
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--- a/kernel/bpf/verifier.c
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+++ b/kernel/bpf/verifier.c
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@@ -2030,7 +2030,6 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env)
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if (IS_ERR(map)) {
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verbose("fd %d is not pointing to valid bpf_map\n",
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insn->imm);
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- fdput(f);
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return PTR_ERR(map);
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}
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--
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2.5.5
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