Re: [PATCH 2/2] regmap: Add range check in _regmap_raw_write()

From: Srinivas Kandagatla
Date: Thu Feb 19 2015 - 06:12:09 EST

On 19/02/15 10:31, Mark Brown wrote:
On Thu, Feb 19, 2015 at 08:40:55AM +0000, Srinivas Kandagatla wrote:
regmap_bulk_write() ends up using the path that invokes _regmap_raw_write(),
however _regmap_raw_write() never checks if the registers that are accessed
are actually within the accessible range. This results in kernel crashes when
trying to access registers beyond max_registers.

This patch just adds check before accessing the register range.

/* Check for unwritable registers before we start */
- if (map->writeable_reg)
- for (i = 0; i < val_len / map->format.val_bytes; i++)
- if (!map->writeable_reg(map->dev,
- reg + (i * map->reg_stride)))
- return -EINVAL;
+ for (i = 0; i < count; i++)
+ if (!regmap_writeable(map, reg + (i * map->reg_stride)))
+ return -EINVAL;

Your changelog doesn't correspond to what the code is actually doing
here... what you're actually doing here is replacing an open coding of
regmap_writeable() with calls to the function.

The same papering over the cracks concerns do apply here as well, it's
not immediately obvious that this is a good fix for the issue you
Only reason for me to send this patch was that fact that _regmap_raw_write() also suffers from same issue as _regmap_raw_read(), which is "access beyond max_register".

Should I drop this patch?
Adding similar check of max_register before the writing makes sense?

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