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Message-Id: <1464112523-3701-41-git-send-email-kamal@canonical.com> Date: Tue, 24 May 2016 10:55:10 -0700 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Jann Horn <jannh@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, "David S . Miller" <davem@...emloft.net>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 4.2.y-ckt 40/53] bpf: fix double-fdput in replace_map_fd_with_map_ptr() 4.2.8-ckt11 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Jann Horn <jannh@...gle.com> [ Upstream commit 8358b02bf67d3a5d8a825070e1aa73f25fb2e4c7 ] When bpf(BPF_PROG_LOAD, ...) was invoked with a BPF program whose bytecode references a non-map file descriptor as a map file descriptor, the error handling code called fdput() twice instead of once (in __bpf_map_get() and in replace_map_fd_with_map_ptr()). If the file descriptor table of the current task is shared, this causes f_count to be decremented too much, allowing the struct file to be freed while it is still in use (use-after-free). This can be exploited to gain root privileges by an unprivileged user. This bug was introduced in commit 0246e64d9a5f ("bpf: handle pseudo BPF_LD_IMM64 insn"), but is only exploitable since commit 1be7f75d1668 ("bpf: enable non-root eBPF programs") because previously, CAP_SYS_ADMIN was required to reach the vulnerable code. (posted publicly according to request by maintainer) Signed-off-by: Jann Horn <jannh@...gle.com> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> Acked-by: Alexei Starovoitov <ast@...nel.org> Acked-by: Daniel Borkmann <daniel@...earbox.net> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- kernel/bpf/verifier.c | 1 - 1 file changed, 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b1f68c2..9718319 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1896,7 +1896,6 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env) if (IS_ERR(map)) { verbose("fd %d is not pointing to valid bpf_map\n", insn->imm); - fdput(f); return PTR_ERR(map); } -- 2.7.4
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