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commit54713c85f5upstream. Lorenzo noticed that the code testing for program type compatibility of tail call maps is potentially racy in that two threads could encounter a map with an unset type simultaneously and both return true even though they are inserting incompatible programs. The race window is quite small, but artificially enlarging it by adding a usleep_range() inside the check in bpf_prog_array_compatible() makes it trivial to trigger from userspace with a program that does, essentially: map_fd = bpf_create_map(BPF_MAP_TYPE_PROG_ARRAY, 4, 4, 2, 0); pid = fork(); if (pid) { key = 0; value = xdp_fd; } else { key = 1; value = tc_fd; } err = bpf_map_update_elem(map_fd, &key, &value, 0); While the race window is small, it has potentially serious ramifications in that triggering it would allow a BPF program to tail call to a program of a different type. So let's get rid of it by protecting the update with a spinlock. The commit in the Fixes tag is the last commit that touches the code in question. v2: - Use a spinlock instead of an atomic variable and cmpxchg() (Alexei) v3: - Put lock and the members it protects into an embedded 'owner' struct (Daniel) Fixes:3324b584b6("ebpf: misc core cleanup") Reported-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211026110019.363464-1-toke@redhat.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.