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Re: [Qemu-devel] [PATCH for v2.3.0] fw_cfg: add check to validate curren
From: |
Stefan Weil |
Subject: |
Re: [Qemu-devel] [PATCH for v2.3.0] fw_cfg: add check to validate current entry value |
Date: |
Tue, 5 Jan 2016 21:22:06 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 |
Am 05.01.2016 um 15:55 schrieb P J P:
> From: Prasad J Pandit <address@hidden>
>
> When processing firmware configurations, an OOB r/w access occurs
> if 's->cur_entry' is set to be invalid(FW_CFG_INVALID=0xffff).
> Add a check to validate 's->cur_entry' to avoid such access.
>
> Reported-by: Donghai Zdh <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
> hw/nvram/fw_cfg.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index 68eff77..ce026bc 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -233,12 +233,15 @@ static void fw_cfg_reboot(FWCfgState *s)
> static void fw_cfg_write(FWCfgState *s, uint8_t value)
> {
> int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
> - FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
> + FWCfgEntry *e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
> + &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
>
> trace_fw_cfg_write(s, value);
>
> - if (s->cur_entry & FW_CFG_WRITE_CHANNEL && e->callback &&
> - s->cur_offset < e->len) {
> + if (s->cur_entry != FW_CFG_INVALID
> + && s->cur_entry & FW_CFG_WRITE_CHANNEL
> + && e->callback
> + && s->cur_offset < e->len) {
I suggest to test e != NULL instead of s->cur_entry != FW_CFG_INVALID.
Of course both variants are equivalent, but e != NULL might be easier
to review and make work of static code analyzers easier, too.
> e->data[s->cur_offset++] = value;
> if (s->cur_offset == e->len) {
> e->callback(e->callback_opaque, e->data);
> @@ -267,7 +270,8 @@ static int fw_cfg_select(FWCfgState *s, uint16_t key)
> static uint8_t fw_cfg_read(FWCfgState *s)
> {
> int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
> - FWCfgEntry *e = &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
> + FWCfgEntry *e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
> + &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
> uint8_t ret;
>
> if (s->cur_entry == FW_CFG_INVALID || !e->data || s->cur_offset >=
> e->len)
>
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