Re: [PATCH v4] w1: therm: Fix off-by-one buffer overflow in alarms_store

[Thorsten Blum]

Hi Krzysztof,

On 11. Nov 2025, at 21:44, Thorsten Blum wrote:
> The sysfs buffer passed to alarms_store() is allocated with 'size + 1'
> bytes and a NUL terminator is appended. However, the 'size' argument
> does not account for this extra byte. The original code then allocated
> 'size' bytes and used strcpy() to copy 'buf', which always writes one
> byte past the allocated buffer since strcpy() copies until the NUL
> terminator at index 'size'.
> 
> Fix this by parsing the 'buf' parameter directly using simple_strtoll()
> without allocating any intermediate memory or string copying. This
> removes the overflow while simplifying the code.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: e2c94d6f5720 ("w1_therm: adding alarm sysfs entry")
> Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
> ---
> Compile-tested only.
> 
> Changes in v4:
> - Use simple_strtoll because kstrtoint also parses long long internally
> - Return -ERANGE in addition to -EINVAL to match kstrtoint's behavior
> - Remove any changes unrelated to fixing the buffer overflow (Krzysztof)
> while maintaining the same behavior and return values as before
> - Link to v3: https://lore.kernel.org/lkml/20251030155614.447905-1-thorsten.blum@xxxxxxxxx/
> 
> Changes in v3:
> - Add integer range check for 'temp' to match kstrtoint() behavior
> - Explicitly cast 'temp' to int when calling int_to_short()
> - Link to v2: https://lore.kernel.org/lkml/20251029130045.70127-2-thorsten.blum@xxxxxxxxx/
> 
> Changes in v2:
> - Fix buffer overflow instead of truncating the copy using strscpy()
> - Parse buffer directly using simple_strtol() as suggested by David
> - Update patch subject and description
> - Link to v1: https://lore.kernel.org/lkml/20251017170047.114224-2-thorsten.blum@xxxxxxxxx/
> ---
> drivers/w1/slaves/w1_therm.c | 64 ++++++++++++------------------------
> 1 file changed, 21 insertions(+), 43 deletions(-)
> [...]

Could you take another look at v4?

Thanks,
Thorsten