[PATCH] xattr: restrict vfs_getxattr_alloc() allocation size

[Seth Forshee]

On Tue, Mar 05, 2024 at 01:27:06PM +0100, Christian Brauner wrote:
> The vfs_getxattr_alloc() interface is a special-purpose in-kernel api
> that does a racy query-size+allocate-buffer+retrieve-data. It is used by
> EVM, IMA, and fscaps to retrieve xattrs. Recently, we've seen issues
> where 9p returned values that amount to allocating about 8000GB worth of
> memory (cf. [1]). That's now fixed in 9p. But vfs_getxattr_alloc() has
> no reason to allow getting xattr values that are larger than
> XATTR_MAX_SIZE as that's the limit we use for setting and getting xattr
> values and nothing currently goes beyond that limit afaict. Let it check
> for that and reject requests that are larger than that.
> 
> Link: https://lore.kernel.org/r/ZeXcQmHWcYvfCR93@do-x1extreme [1]
> Signed-off-by: Christian Brauner <brauner at kernel.org>

Makes sense.

Reviewed-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>