Re: [PATCH] ftrace: fix NULL pointer dereference in free_ftrace_func_mapper()

[Steven Rostedt]

On Thu, 6 Jun 2019 11:17:54 +0800
Wei Li <liwei391@xxxxxxxxxx> wrote:

> The mapper may be NULL when called from register_ftrace_function_probe()
> with probe->data == NULL.
> 
> This issue can be reproduced as follow (it may be coverd by compiler
> optimization sometime):
> 
> / # cat /sys/kernel/debug/tracing/set_ftrace_filter 

I'm not able to reproduce this, but I have nothing against the patch.
It seems like a sane test. We can probably remove all the:

  if (!mapper)
	return;

before callers of this function then.

I'll apply this for my next push to Linus.

-- Steve

> #### all functions enabled ####
> / # echo foo_bar:dump > /sys/kernel/debug/tracing/set_ftrace_filter 
> [  206.949100] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> [  206.952402] Mem abort info:
> [  206.952819]   ESR = 0x96000006
> [  206.955326]   Exception class = DABT (current EL), IL = 32 bits
> [  206.955844]   SET = 0, FnV = 0
> [  206.956272]   EA = 0, S1PTW = 0
> [  206.956652] Data abort info:
> [  206.957320]   ISV = 0, ISS = 0x00000006
> [  206.959271]   CM = 0, WnR = 0
> [  206.959938] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000419f3a000
> [  206.960483] [0000000000000000] pgd=0000000411a87003, pud=0000000411a83003, pmd=0000000000000000
> [  206.964953] Internal error: Oops: 96000006 [#1] SMP
> [  206.971122] Dumping ftrace buffer:
> [  206.973677]    (ftrace buffer empty)
> [  206.975258] Modules linked in:
> [  206.976631] Process sh (pid: 281, stack limit = 0x(____ptrval____))
> [  206.978449] CPU: 10 PID: 281 Comm: sh Not tainted 5.2.0-rc1+ #17
> [  206.978955] Hardware name: linux,dummy-virt (DT)
> [  206.979883] pstate: 60000005 (nZCv daif -PAN -UAO)
> [  206.980499] pc : free_ftrace_func_mapper+0x2c/0x118
> [  206.980874] lr : ftrace_count_free+0x68/0x80
> [  206.982539] sp : ffff0000182f3ab0
> [  206.983102] x29: ffff0000182f3ab0 x28: ffff8003d0ec1700 
> [  206.983632] x27: ffff000013054b40 x26: 0000000000000001 
> [  206.984000] x25: ffff00001385f000 x24: 0000000000000000 
> [  206.984394] x23: ffff000013453000 x22: ffff000013054000 
> [  206.984775] x21: 0000000000000000 x20: ffff00001385fe28 
> [  206.986575] x19: ffff000013872c30 x18: 0000000000000000 
> [  206.987111] x17: 0000000000000000 x16: 0000000000000000 
> [  206.987491] x15: ffffffffffffffb0 x14: 0000000000000000 
> [  206.987850] x13: 000000000017430e x12: 0000000000000580 
> [  206.988251] x11: 0000000000000000 x10: cccccccccccccccc 
> [  206.988740] x9 : 0000000000000000 x8 : ffff000013917550 
> [  206.990198] x7 : ffff000012fac2e8 x6 : ffff000012fac000 
> [  206.991008] x5 : ffff0000103da588 x4 : 0000000000000001 
> [  206.991395] x3 : 0000000000000001 x2 : ffff000013872a28 
> [  206.991771] x1 : 0000000000000000 x0 : 0000000000000000 
> [  206.992557] Call trace:
> [  206.993101]  free_ftrace_func_mapper+0x2c/0x118
> [  206.994827]  ftrace_count_free+0x68/0x80
> [  206.995238]  release_probe+0xfc/0x1d0
> [  206.995555]  register_ftrace_function_probe+0x4a8/0x868
> [  206.995923]  ftrace_trace_probe_callback.isra.4+0xb8/0x180
> [  206.996330]  ftrace_dump_callback+0x50/0x70
> [  206.996663]  ftrace_regex_write.isra.29+0x290/0x3a8
> [  206.997157]  ftrace_filter_write+0x44/0x60
> [  206.998971]  __vfs_write+0x64/0xf0
> [  206.999285]  vfs_write+0x14c/0x2f0
> [  206.999591]  ksys_write+0xbc/0x1b0
> [  206.999888]  __arm64_sys_write+0x3c/0x58
> [  207.000246]  el0_svc_common.constprop.0+0x408/0x5f0
> [  207.000607]  el0_svc_handler+0x144/0x1c8
> [  207.000916]  el0_svc+0x8/0xc
> [  207.003699] Code: aa0003f8 a9025bf5 aa0103f5 f946ea80 (f9400303) 
> [  207.008388] ---[ end trace 7b6d11b5f542bdf1 ]---
> [  207.010126] Kernel panic - not syncing: Fatal exception
> [  207.011322] SMP: stopping secondary CPUs
> [  207.013956] Dumping ftrace buffer:
> [  207.014595]    (ftrace buffer empty)
> [  207.015632] Kernel Offset: disabled
> [  207.017187] CPU features: 0x002,20006008
> [  207.017985] Memory Limit: none
> [  207.019825] ---[ end Kernel panic - not syncing: Fatal exception ]---
> 
> Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
> ---
>  kernel/trace/ftrace.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index a12aff849c04..7e2488da69ac 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4221,10 +4221,13 @@ void free_ftrace_func_mapper(struct ftrace_func_mapper *mapper,
>  	struct ftrace_func_entry *entry;
>  	struct ftrace_func_map *map;
>  	struct hlist_head *hhd;
> -	int size = 1 << mapper->hash.size_bits;
> -	int i;
> +	int size, i;
> +
> +	if (!mapper)
> +		return;
>  
>  	if (free_func && mapper->hash.count) {
> +		size = 1 << mapper->hash.size_bits;
>  		for (i = 0; i < size; i++) {
>  			hhd = &mapper->hash.buckets[i];
>  			hlist_for_each_entry(entry, hhd, hlist) {