Patch "bpf: fix double-fdput in replace_map_fd_with_map_ptr()" has been added to the 4.5-stable tree

This is a note to let you know that I've just added the patch titled

bpf: fix double-fdput in replace_map_fd_with_map_ptr()

to the 4.5-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-double-fdput-in-replace_map_fd_with_map_ptr.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jann Horn <[email protected]>
Date: Tue, 26 Apr 2016 22:26:26 +0200
Subject: bpf: fix double-fdput in replace_map_fd_with_map_ptr()

From: Jann Horn <[email protected]>

[ 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)

---
 kernel/bpf/verifier.c |    1 -
 1 file changed, 1 deletion(-)

@@ -2004,7 +2004,6 @@ static int replace_map_fd_with_map_ptr(s
 			if (IS_ERR(map)) {
 				verbose("fd %d is not pointing to valid bpf_map\n",
 					insn->imm);
-				fdput(f);
 				return PTR_ERR(map);
 			}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/bpf-fix-double-fdput-in-replace_map_fd_with_map_ptr.patch queue-4.5/bpf-fix-refcnt-overflow.patch queue-4.5/bpf-fix-check_map_func_compatibility-logic.patch