In the Linux kernel, the following vulnerability has been resolved:
bpf: Prevent tailcall infinite loop caused by freplace
There is a potential infinite loop issue that can occur when using a combination of tail calls and freplace.
In an upcoming selftest, the attach target for entry_freplace of tailcall_freplace.c is subprog_tc of tc_bpf2bpf.c, while the tail call in entry_freplace leads to entry_tc. This results in an infinite loop:
entry_tc -> subprog_tc -> entry_freplace --tailcall-> entry_tc.
The problem arises because the tail_call_cnt in entry_freplace resets to zero each time entry_freplace is executed, causing the tail call mechanism to never terminate, eventually leading to a kernel panic.
To fix this issue, the solution is twofold:
This ensures that:
Moreover, an extension program should not be tailcalled. As such, return -EINVAL if the program has a type of BPF_PROG_TYPE_EXT when adding it to a prog_array map.
Additionally, fix a minor code style issue by replacing eight spaces with a tab for proper formatting.