[PATCH] mtd: physmap: physmap-bt1-rom: Fix unintentional stack access
miquel.raynal at bootlin.com
Fri Feb 12 09:50:31 EST 2021
"Gustavo A. R. Silva" <gustavo at embeddedor.com> wrote on Fri, 12 Feb
2021 08:45:33 -0600:
> On 2/12/21 08:12, Miquel Raynal wrote:
> > Hi Gustavo,
> > "Gustavo A. R. Silva" <gustavoars at kernel.org> wrote on Fri, 12 Feb 2021
> > 04:40:22 -0600:
> >> Cast &data to (char *) in order to avoid unintentionally accessing
> >> the stack.
> >> Notice that data is of type u32, so any increment to &data
> >> will be in the order of 4-byte chunks, and this piece of code
> >> is actually intended to be a byte offset.
> > I don't have the same reading. I don't say that Coverity report is
> > wrong, but let's discuss this a bit further.
> > Given that &data is of type u32 *, you say that "&data + shift"
> > produces increments of 4-bytes, ie. we would access "&data + 4 *
> > shift"? Because I don't think this is the case (again, I may be wrong).
> Yep; this is pointer arithmetic. If you have an object ptr of type u32 *:
> u32 *ptr;
> and let's say it points to address 100. If you increment it by one:
> ptr will now point to address 104, not to 101.
> Now, if instead, you first cast ptr to 'char *' and increment it by 1,
> then it will point to address 101.
Yep, I got confused with the proper addition compared to dereferencing.
Patch looks legitimate.
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