bpf: do not disable/enable BH in bpf_map_free_id()

Eric Dumazet · davem330 · commit 930651a75bf1 · 2017-09-19T15:42:54.000-07:00
syzkaller reported following splat [1] Since hard irq are disabled by the caller, bpf_map_free_id() should not try to enable/disable BH. Another solution would be to change htab_map_delete_elem() to defer the free_htab_elem() call after raw_spin_unlock_irqrestore(&b->lock, flags), but this might be not enough to cover other code paths. [1] WARNING: CPU: 1 PID: 8052 at kernel/softirq.c:161 __local_bh_enable_ip +0x1e/0x160 kernel/softirq.c:161 Kernel panic - not syncing: panic_on_warn set ... CPU: 1 PID: 8052 Comm: syz-executor1 Not tainted 4.13.0-next-20170915+ torvalds#23 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 panic+0x1e4/0x417 kernel/panic.c:181 __warn+0x1c4/0x1d9 kernel/panic.c:542 report_bug+0x211/0x2d0 lib/bug.c:183 fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:178 do_trap_no_signal arch/x86/kernel/traps.c:212 [inline] do_trap+0x260/0x390 arch/x86/kernel/traps.c:261 do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:298 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:311 invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905 RIP: 0010:__local_bh_enable_ip+0x1e/0x160 kernel/softirq.c:161 RSP: 0018:ffff8801cdcd7748 EFLAGS: 00010046 RAX: 0000000000000082 RBX: 0000000000000201 RCX: 0000000000000000 RDX: 1ffffffff0b5933c RSI: 0000000000000201 RDI: ffffffff85ac99e0 RBP: ffff8801cdcd7758 R08: ffffffff85b87158 R09: 1ffff10039b9aec6 R10: ffff8801c99f24c0 R11: 0000000000000002 R12: ffffffff817b0b47 R13: dffffc0000000000 R14: ffff8801cdcd77e8 R15: 0000000000000001 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:176 [inline] _raw_spin_unlock_bh+0x30/0x40 kernel/locking/spinlock.c:207 spin_unlock_bh include/linux/spinlock.h:361 [inline] bpf_map_free_id kernel/bpf/syscall.c:197 [inline] __bpf_map_put+0x267/0x320 kernel/bpf/syscall.c:227 bpf_map_put+0x1a/0x20 kernel/bpf/syscall.c:235 bpf_map_fd_put_ptr+0x15/0x20 kernel/bpf/map_in_map.c:96 free_htab_elem+0xc3/0x1b0 kernel/bpf/hashtab.c:658 htab_map_delete_elem+0x74d/0x970 kernel/bpf/hashtab.c:1063 map_delete_elem kernel/bpf/syscall.c:633 [inline] SYSC_bpf kernel/bpf/syscall.c:1479 [inline] SyS_bpf+0x2188/0x46a0 kernel/bpf/syscall.c:1451 entry_SYSCALL_64_fastpath+0x1f/0xbe Fixes: f3f1c05 ("bpf: Introduce bpf_map ID") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Martin KaFai Lau <kafai@fb.com> Acked-by: Martin KaFai Lau <kafai@fb.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
@@ -186,15 +186,17 @@ static int bpf_map_alloc_id(struct bpf_map *map)
 
 static void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock)
 {
+	unsigned long flags;
+
 	if (do_idr_lock)
-		spin_lock_bh(&map_idr_lock);
+		spin_lock_irqsave(&map_idr_lock, flags);
 	else
 		__acquire(&map_idr_lock);
 
 	idr_remove(&map_idr, map->id);
 
 	if (do_idr_lock)
-		spin_unlock_bh(&map_idr_lock);
+		spin_unlock_irqrestore(&map_idr_lock, flags);
 	else
 		__release(&map_idr_lock);
 }
