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From: Al Viro <viro@zeniv.linux.org.uk>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	David Laight <David.Laight@aculab.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
	linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-s390@vger.kernel.org, sparclinux@vger.kernel.org,
	linux-block@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
	io-uring@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, netdev@vger.kernel.org,
	keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec
Date: Wed, 23 Sep 2020 15:40:25 +0100
Message-ID: <20200923144025.GL3421308@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200923141654.GJ3421308@ZenIV.linux.org.uk>

On Wed, Sep 23, 2020 at 03:16:54PM +0100, Al Viro wrote:
> On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote:
> 
> > +struct iovec *iovec_from_user(const struct iovec __user *uvec,
> > +		unsigned long nr_segs, unsigned long fast_segs,
> 
> Hmm...  For fast_segs unsigned long had always been ridiculous
> (4G struct iovec on caller stack frame?), but that got me wondering about
> nr_segs and I wish I'd thought of that when introducing import_iovec().
> 
> The thing is, import_iovec() takes unsigned int there.  Which is fine
> (hell, the maximal value that can be accepted in 1024), except that
> we do pass unsigned long syscall argument to it in some places.
> 
> E.g. vfs_readv() quietly truncates vlen to 32 bits, and vlen can
> come unchanged through sys_readv() -> do_readv() -> vfs_readv().
> With unsigned long passed by syscall glue.
> 
> AFAICS, passing 4G+1 as the third argument to readv(2) on 64bit box
> will be quietly treated as 1 these days.  Which would be fine, except
> that before "switch {compat_,}do_readv_writev() to {compat_,}import_iovec()"
> it used to fail with -EINVAL.
> 
> Userland, BTW, describes readv(2) iovcnt as int; process_vm_readv(),
> OTOH, has these counts unsigned long from the userland POV...
> 
> I suppose we ought to switch import_iovec() to unsigned long for nr_segs ;-/
> Strictly speaking that had been a userland ABI change, even though nothing
> except regression tests checking for expected errors would've been likely
> to notice.  And it looks like no regression tests covered that one...
> 
> Linus, does that qualify for your "if no userland has noticed the change,
> it's not a breakage"?

Egads...  We have sys_readv() with unsigned long for file descriptor, since
1.3.31 when it had been introduced.  And originally it did comparison with
NR_OPEN right in sys_readv().  Then in 2.1.60 it had been switched to
fget(), which used to take unsigned long at that point.  And in 2.1.90pre1
it went unsigned int, so non-zero upper 32 bits in readv(2) first argument
ceased to cause EBADF...

Of course, libc had it as int fd all along.

  parent reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-23  6:05 let import_iovec deal with compat_iovecs as well v3 Christoph Hellwig
2020-09-23  6:05 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-23  6:05 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-09-23  6:05 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-23 14:16   ` Al Viro
2020-09-23 14:38     ` David Laight
2020-09-23 14:49       ` Al Viro
2020-09-23 14:40     ` Al Viro [this message]
2020-09-23  6:05 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-23  6:05 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-23 14:25   ` Al Viro
2020-09-23 14:32     ` Christoph Hellwig
2020-09-23 14:59       ` Al Viro
2020-09-23 16:38         ` Al Viro
2020-09-23 17:05           ` Al Viro
2020-09-23 17:46             ` Christoph Hellwig
2020-09-23 17:08           ` Brian Gerst
2020-09-23 18:45           ` Arnd Bergmann
2020-09-23 19:47             ` Al Viro
2020-09-23 19:52               ` Arnd Bergmann
2020-09-23 21:30             ` David Laight
2020-09-23  6:05 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-23  6:05 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-23  6:05 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-23  6:05 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
2020-09-25  4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25  4:51 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig

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