Hi!
From: Vivien Didelot vivien.didelot@gmail.com
[ Upstream commit 0ee4e76937d69128a6a66861ba393ebdc2ffc8a2 ]
ethtool_get_regs() allocates a buffer of size ops->get_regs_len(), and pass it to the kernel driver via ops->get_regs() for filling.
There is no restriction about what the kernel drivers can or cannot do with the open ethtool_regs structure. They usually set regs->version and ignore regs->len or set it to the same size as ops->get_regs_len().
But if userspace allocates a smaller buffer for the registers dump, we would cause a userspace buffer overflow in the final copy_to_user() call, which uses the regs.len value potentially reset by the driver.
To fix this, make this case obvious and store regs.len before calling ops->get_regs(), to only copy as much data as requested by userspace, up to the value returned by ops->get_regs_len().
While at it, remove the redundant check for non-null regbuf.
Mainline differs from 4.19-stable here, and while the non-null check is redundant in -mainline, it does not seem to be redundant in -stable.
In stable, if get_regs_len() returns < 0, we'll pass it to vzalloc.
Pavel