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 <ja...@google.com>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
---
kernel/bpf/verifier.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2e08f8e..8291251 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2029,7 +2029,6 @@ 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);
}
--
2.8.0.rc3.226.g39d4020
