mtd: physmap: physmap-bt1-rom: Fix unintentional stack access

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.

Fixes b3e79e7682e0 ("mtd: physmap: Add Baikal-T1 physically mapped ROM support")

Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
 drivers/mtd/maps/physmap-bt1-rom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/mtd/maps/physmap-bt1-rom.c +0 -0

index a35450002284..58782cfaf71c 100644

Hi Gustavo,

"Gustavo A. R. Silva" <[email protected]> wrote on Fri, 12 Feb 2021 04:40:22 -0600:

Quoted 6 lines

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).

I'm sure this would be the case if we dereferenced data like data[shift] though, but in this case I don't see what this cast is fixing. Can you enlighten me?

Could the out-of-bounds warning come from the fact that shift might be bigger than the data array spread?

Quoted 9 lines

Fixes b3e79e7682e0 ("mtd: physmap: Add Baikal-T1 physically mapped ROM support")

Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
 drivers/mtd/maps/physmap-bt1-rom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/mtd/maps/physmap-bt1-rom.c static void __xipram bt1_rom_map_copy_from(struct map_info *map, · line 85

Quoted 13 lines

drivers/mtd/maps/physmap-bt1-rom.c +1 -1

index a35450002284..58782cfaf71c 100644
@@ -79,7 +79,7 @@ static void __xipram bt1_rom_map_copy_from(struct map_info *map,
 	if (shift) {
 		chunk = min_t(ssize_t, 4 - shift, len);
 		data = readl_relaxed(src - shift);
-		memcpy(to, &data + shift, chunk);
+		memcpy(to, (char *)&data + shift, chunk);
 		src += chunk;
 		to += chunk;
 		len -= chunk;

Thanks,
Miquèl

Quoted 12 lines

Hi Gustavo,

"Gustavo A. R. Silva" <[email protected]> wrote on Fri, 12 Feb 2021 04:40:22 -0600:

Quoted 6 lines

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.

Quoted 6 lines

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++

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.

Quoted 2 lines

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.

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.

Fixes b3e79e7682e0 ("mtd: physmap: Add Baikal-T1 physically mapped ROM support")

Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
 drivers/mtd/maps/physmap-bt1-rom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/mtd/maps/physmap-bt1-rom.c +1 -1

index a35450002284..58782cfaf71c 100644
@@ -79,7 +79,7 @@ static void __xipram bt1_rom_map_copy_from(struct map_info *map,
 	if (shift) {
 		chunk = min_t(ssize_t, 4 - shift, len);
 		data = readl_relaxed(src - shift);
-		memcpy(to, &data + shift, chunk);
+		memcpy(to, (char *)&data + shift, chunk);
 		src += chunk;
 		to += chunk;
 		len -= chunk;

Signature · 1 line

2.27.0

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.

Fixes b3e79e7682e0 ("mtd: physmap: Add Baikal-T1 physically mapped ROM support")

Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

Acked-by Serge Semin <[email protected]>