CVE-2026-31412usb: gadget: f_mass_storage: Fix potential integer overflow in check_command_size_in_blocks()

Official description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_mass_storage: Fix potential integer overflow in check_command_size_in_blocks() The `check_command_size_in_blocks()` function calculates the data size in bytes by left shifting `common->data_size_from_cmnd` by the block size (`common->curlun->blkbits`). However, it does not validate whether this shift operation will cause an integer overflow. Initially, the block size is set up in `fsg_lun_open()` , and the `common->data_size_from_cmnd` is set up in `do_scsi_command()`. During initialization, there is no integer overflow check for the interaction between two variables. So if a malicious USB host sends a SCSI READ or WRITE command requesting a large amount of data (`common->data_size_from_cmnd`), the left shift operation can wrap around. This results in a truncated data size, which can bypass boundary checks and potentially lead to memory corruption or out-of-bounds accesses. Fix this by using the check_shl_overflow() macro to safely perform the shift and catch any overflows.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/91817ad5452defe69bc7bc0e355f0ed5d01125cc
• https://git.kernel.org/stable/c/ce0caaed5940162780c5c223b8ae54968a5f059b
• https://git.kernel.org/stable/c/228b37936376143f4b60cc6828663f6eaceb81b5
• https://git.kernel.org/stable/c/3428dc5520c811e66622b2f5fa43341bf9a1f8b3
• https://git.kernel.org/stable/c/387ebb0453b99d71491419a5dc4ab4bee0cacbac
• https://git.kernel.org/stable/c/8479891d1f04a8ce55366fe4ca361ccdb96f02e1