From cbb766766f3f2f6d9326c561b1020590642c6e39 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Fri, 27 Feb 2009 14:03:04 -0800 Subject: [PATCH] mm: fix lazy vmap purging (use-after-free error) I just got this new warning from kmemcheck: WARNING: kmemcheck: Caught 32-bit read from freed memory (c7806a60) a06a80c7ecde70c1a04080c700000000a06709c1000000000000000000000000 f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f f ^ Pid: 0, comm: swapper Not tainted (2.6.29-rc4 #230) EIP: 0060:[] EFLAGS: 00000286 CPU: 0 EIP is at __purge_vmap_area_lazy+0x117/0x140 EAX: 00070f43 EBX: c7806a40 ECX: c1677080 EDX: 00027b66 ESI: 00002001 EDI: c170df0c EBP: c170df00 ESP: c178830c DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 CR0: 80050033 CR2: c7806b14 CR3: 01775000 CR4: 00000690 DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 DR6: 00004000 DR7: 00000000 [] free_unmap_vmap_area_noflush+0x6e/0x70 [] remove_vm_area+0x2a/0x70 [] __vunmap+0x45/0xe0 [] vunmap+0x1e/0x30 [] text_poke+0x95/0x150 [] alternatives_smp_unlock+0x49/0x60 [] alternative_instructions+0x11b/0x124 [] check_bugs+0xbd/0xdc [] start_kernel+0x2ed/0x360 [] __init_begin+0x9e/0xa9 [] 0xffffffff It happened here: $ addr2line -e vmlinux -i c1096df7 mm/vmalloc.c:540 Code: list_for_each_entry(va, &valist, purge_list) __free_vmap_area(va); It's this instruction: mov 0x20(%ebx),%edx Which corresponds to a dereference of va->purge_list.next: (gdb) p ((struct vmap_area *) 0)->purge_list.next Cannot access memory at address 0x20 It seems that we should use "safe" list traversal here, as the element is freed inside the loop. Please verify that this is the right fix. Acked-by: Nick Piggin Signed-off-by: Vegard Nossum Cc: Pekka Enberg Cc: Ingo Molnar Cc: "Paul E. McKenney" Cc: [2.6.28.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmalloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index ed3705e..520a759 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -505,6 +505,7 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, static DEFINE_SPINLOCK(purge_lock); LIST_HEAD(valist); struct vmap_area *va; + struct vmap_area *n_va; int nr = 0; /* @@ -544,7 +545,7 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, if (nr) { spin_lock(&vmap_area_lock); - list_for_each_entry(va, &valist, purge_list) + list_for_each_entry_safe(va, n_va, &valist, purge_list) __free_vmap_area(va); spin_unlock(&vmap_area_lock); } -- 2.7.4