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authorToke Høiland-Jørgensen <toke@redhat.com>2021-10-26 14:00:19 +0300
committerAlexei Starovoitov <ast@kernel.org>2021-10-26 22:37:28 +0300
commit54713c85f536048e685258f880bf298a74c3620d (patch)
treea3641b7d50d144bb45f184aea271f72b34ff85a7 /include/linux
parent99d0a3831e3500d945162cdb2310e3a5fce90b60 (diff)
downloadlinux-54713c85f536048e685258f880bf298a74c3620d.tar.xz
bpf: Fix potential race in tail call compatibility check
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: 3324b584b6f6 ("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
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/bpf.h7
1 files changed, 5 insertions, 2 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 020a7d5bf470..3db6f6c95489 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -929,8 +929,11 @@ struct bpf_array_aux {
* stored in the map to make sure that all callers and callees have
* the same prog type and JITed flag.
*/
- enum bpf_prog_type type;
- bool jited;
+ struct {
+ spinlock_t lock;
+ enum bpf_prog_type type;
+ bool jited;
+ } owner;
/* Programs with direct jumps into programs part of this array. */
struct list_head poke_progs;
struct bpf_map *map;