strlen_user and keys

strlen_user and keys

[Andries.Brouwer]

[faraway from home, not near recent kernel source]

strnlen_user() is documented as returning the string length including
terminating NUL. Probably that was a bad idea - people expect that
if user space and kernel library functions have similar names, they do
similar things. The shouting "INCLUDING" in the description already
shows that also the author expected that bugs would be created by
using this name.

[see, e.g., arch/i386/lib/usercopy.c]

security/keys/keyctl.c does

        dlen = strnlen_user(_description, PAGE_SIZE - 1);
	description = kmalloc(dlen + 1, GFP_KERNEL);
	copy_from_user(description, _description, dlen + 1);

copying one byte too many.
(Thus in some unknown kernel source tree, maybe 2.6.14.
This may have been fixed already.)

Andries

Re: strlen_user and keys

[David Howells]

<Andries.Brouwer@cwi.nl> wrote:

> strnlen_user() is documented as returning the string length including
> terminating NUL.

There's now a strndup_user() in Linus's git tree.

> security/keys/keyctl.c does

This now uses strndup_user().

David