Re: [PATCH bpf v2 3/7] bpf: Preserve param->string when parsing mount options

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Oct 21, 2024 at 09:40:00AM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> In bpf_parse_param(), keep the value of param->string intact so it can
> be freed later. Otherwise, the kmalloc area pointed to by param->string
> will be leaked as shown below:
> 
> unreferenced object 0xffff888118c46d20 (size 8):
>   comm "new_name", pid 12109, jiffies 4295580214
>   hex dump (first 8 bytes):
>     61 6e 79 00 38 c9 5c 7e                          any.8.\~
>   backtrace (crc e1b7f876):
>     [<00000000c6848ac7>] kmemleak_alloc+0x4b/0x80
>     [<00000000de9f7d00>] __kmalloc_node_track_caller_noprof+0x36e/0x4a0
>     [<000000003e29b886>] memdup_user+0x32/0xa0
>     [<0000000007248326>] strndup_user+0x46/0x60
>     [<0000000035b3dd29>] __x64_sys_fsconfig+0x368/0x3d0
>     [<0000000018657927>] x64_sys_call+0xff/0x9f0
>     [<00000000c0cabc95>] do_syscall_64+0x3b/0xc0
>     [<000000002f331597>] entry_SYSCALL_64_after_hwframe+0x4b/0x53
> 
> Fixes: 6c1752e0b6ca ("bpf: Support symbolic BPF FS delegation mount options")
> Signed-off-by: Hou Tao <houtao1@huawei.com>

nice, I saw that memleak report recently and couldn't make sense of it ;-)

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
>  kernel/bpf/inode.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
> index d8fc5eba529d..9aaf5124648b 100644
> --- a/kernel/bpf/inode.c
> +++ b/kernel/bpf/inode.c
> @@ -880,7 +880,7 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  		const struct btf_type *enum_t;
>  		const char *enum_pfx;
>  		u64 *delegate_msk, msk = 0;
> -		char *p;
> +		char *p, *str;
>  		int val;
>  
>  		/* ignore errors, fallback to hex */
> @@ -911,7 +911,8 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  			return -EINVAL;
>  		}
>  
> -		while ((p = strsep(&param->string, ":"))) {
> +		str = param->string;
> +		while ((p = strsep(&str, ":"))) {
>  			if (strcmp(p, "any") == 0) {
>  				msk |= ~0ULL;
>  			} else if (find_btf_enum_const(info.btf, enum_t, enum_pfx, p, &val)) {
> -- 
> 2.29.2
>