Since commit 1c123c567fb138eb ("bpf: Resolve fext program type when
checking map compatibility"), freplace prog can be used as tail-callee.
However, when freplace prog has been attached and then updates to
PROG_ARRAY map, it will panic, because the updating checks prog type of
freplace prog by 'prog->aux->dst_prog->type' and 'prog->aux->dst_prog' of
freplace prog is NULL.
[309049.036402] BUG: kernel NULL pointer dereference, address: 0000000000000004
[309049.036419] #PF: supervisor read access in kernel mode
[309049.036426] #PF: error_code(0x0000) - not-present page
[309049.036432] PGD 0 P4D 0
[309049.036437] Oops: 0000 [#1] PREEMPT SMP NOPTI
[309049.036444] CPU: 2 PID: 788148 Comm: test_progs Not tainted 6.8.0-31-generic #31-Ubuntu
[309049.036465] Hardware name: VMware, Inc. VMware20,1/440BX Desktop Reference Platform, BIOS VMW201.00V.21805430.B64.2305221830 05/22/2023
[309049.036477] RIP: 0010:bpf_prog_map_compatible+0x2a/0x140
[309049.036488] Code: 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 49 89 fe 41 55 41 54 53 44 8b 6e 04 48 89 f3 41 83 fd 1c 75 0c 48 8b 46 38 48 8b 40 70 <44> 8b 68 04 f6 43 03 01 75 1c 48 8b 43 38 44 0f b6 a0 89 00 00 00
[309049.036505] RSP: 0018:ffffb2e080fd7ce0 EFLAGS: 00010246
[309049.036513] RAX: 0000000000000000 RBX: ffffb2e0807c1000 RCX: 0000000000000000
[309049.036521] RDX: 0000000000000000 RSI: ffffb2e0807c1000 RDI: ffff990290259e00
[309049.036528] RBP: ffffb2e080fd7d08 R08: 0000000000000000 R09: 0000000000000000
[309049.036536] R10: 0000000000000000 R11: 0000000000000000 R12: ffff990290259e00
[309049.036543] R13: 000000000000001c R14: ffff990290259e00 R15: ffff99028e29c400
[309049.036551] FS: 00007b82cbc28140(0000) GS:ffff9903b3f00000(0000) knlGS:0000000000000000
[309049.036559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[309049.036566] CR2: 0000000000000004 CR3: 0000000101286002 CR4: 00000000003706f0
[309049.036573] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[309049.036581] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[309049.036588] Call Trace:
[309049.036592] <TASK>
[309049.036597] ? show_regs+0x6d/0x80
[309049.036604] ? __die+0x24/0x80
[309049.036619] ? page_fault_oops+0x99/0x1b0
[309049.036628] ? do_user_addr_fault+0x2ee/0x6b0
[309049.036634] ? exc_page_fault+0x83/0x1b0
[309049.036641] ? asm_exc_page_fault+0x27/0x30
[309049.036649] ? bpf_prog_map_compatible+0x2a/0x140
[309049.036656] prog_fd_array_get_ptr+0x2c/0x70
[309049.036664] bpf_fd_array_map_update_elem+0x37/0x130
[309049.036671] bpf_map_update_value+0x1d3/0x260
[309049.036677] map_update_elem+0x1fa/0x360
[309049.036683] __sys_bpf+0x54c/0xa10
[309049.036689] __x64_sys_bpf+0x1a/0x30
[309049.036694] x64_sys_call+0x1936/0x25c0
[309049.036700] do_syscall_64+0x7f/0x180
[309049.036706] ? do_syscall_64+0x8c/0x180
[309049.036712] ? do_syscall_64+0x8c/0x180
[309049.036717] ? irqentry_exit+0x43/0x50
[309049.036723] ? common_interrupt+0x54/0xb0
[309049.036729] entry_SYSCALL_64_after_hwframe+0x73/0x7b
Why 'prog->aux->dst_prog' of freplace prog is NULL? It causes by commit 3aac1ead5eb6
("bpf: Move prog->aux->linked_prog and trampoline into bpf_link on attach").
As 'prog->aux->dst_prog' of freplace prog is set as NULL when attach,
freplace prog does not have stable prog type. But when to update
freplace prog to PROG_ARRAY map, it requires checking prog type. They are
conflict in theory.
This patch is unable to resolve this issue thoroughly. It resolves prog
type of freplace prog by 'prog->aux->saved_dst_prog_type' to avoid panic.
Fixes: 1c123c567fb1 ("bpf: Resolve fext program type when checking map compatibility")
Signed-off-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
---
include/linux/bpf_verifier.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 50aa87f8d77ff..b648a96ca310b 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -845,7 +845,7 @@ static inline u32 type_flag(u32 type)
static inline enum bpf_prog_type resolve_prog_type(const struct bpf_prog *prog)
{
return prog->type == BPF_PROG_TYPE_EXT ?
- prog->aux->dst_prog->type : prog->type;
+ prog->aux->saved_dst_prog_type : prog->type;
}
static inline bool bpf_prog_check_recur(const struct bpf_prog *prog)
--
2.44.0
