[3.19.y-ckt stable] Patch "bpf: fix double-fdput in replace_map_fd_with_map_ptr()" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    bpf: fix double-fdput in replace_map_fd_with_map_ptr()

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From d22bb0f0b558e213b31eb04e2e3afbe8d5c6702b Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh at google.com>
Date: Tue, 26 Apr 2016 22:26:26 +0200
Subject: bpf: fix double-fdput in replace_map_fd_with_map_ptr()

[ 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 at google.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Acked-by: Alexei Starovoitov <ast at kernel.org>
Acked-by: Daniel Borkmann <daniel at iogearbox.net>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/bpf/verifier.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0d2cbc9..45fdf5c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1817,7 +1817,6 @@ 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