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Date: Tue, 7 Nov 2023 06:18:41 +0100
From: Damian Tometzki <damian@...cv-rocks.de>
To: David Howells <dhowells@...hat.com>
Cc: Damian Tometzki <damian@...cv-rocks.de>,
Eric Biggers <ebiggers@...nel.org>,
Steve French <smfrench@...il.com>,
John Sanpe <sanpeqf@...il.com>,
CIFS <linux-cifs@...r.kernel.org>,
Namjae Jeon <linkinjeon@...nel.org>,
Paulo Alcantara <pc@...guebit.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cifs: Fix encryption of cleared, but unset rq_iter data
buffers
On Mon, 06. Nov 14:40, David Howells wrote:
> Hi Damian,
>
> Does the attached fix it for you?
Hello David,
this fix my issue with the cifs mount.
Great many Thanks
Damian
>
> David
> ---
> cifs: Fix encryption of cleared, but unset rq_iter data buffers
>
> Each smb_rqst struct contains two things: an array of kvecs (rq_iov) that
> contains the protocol data for an RPC op and an iterator (rq_iter) that
> contains the data payload of an RPC op. When an smb_rqst is allocated
> rq_iter is it always cleared, but we don't set it up unless we're going to
> use it.
>
> The functions that determines the size of the ciphertext buffer that will
> be needed to encrypt a request, cifs_get_num_sgs(), assumes that rq_iter is
> always initialised - and employs user_backed_iter() to check that the
> iterator isn't user-backed. This used to incidentally work, because
> ->user_backed was set to false because the iterator has never been
> initialised, but with commit f1b4cb650b9a0eeba206d8f069fcdc532bfbcd74[1]
> which changes user_backed_iter() to determine this based on the iterator
> type insted, a warning is now emitted:
>
> WARNING: CPU: 7 PID: 4584 at fs/smb/client/cifsglob.h:2165 smb2_get_aead_req+0x3fc/0x420 [cifs]
> ...
> RIP: 0010:smb2_get_aead_req+0x3fc/0x420 [cifs]
> ...
> crypt_message+0x33e/0x550 [cifs]
> smb3_init_transform_rq+0x27d/0x3f0 [cifs]
> smb_send_rqst+0xc7/0x160 [cifs]
> compound_send_recv+0x3ca/0x9f0 [cifs]
> cifs_send_recv+0x25/0x30 [cifs]
> SMB2_tcon+0x38a/0x820 [cifs]
> cifs_get_smb_ses+0x69c/0xee0 [cifs]
> cifs_mount_get_session+0x76/0x1d0 [cifs]
> dfs_mount_share+0x74/0x9d0 [cifs]
> cifs_mount+0x6e/0x2e0 [cifs]
> cifs_smb3_do_mount+0x143/0x300 [cifs]
> smb3_get_tree+0x15e/0x290 [cifs]
> vfs_get_tree+0x2d/0xe0
> do_new_mount+0x124/0x340
> __se_sys_mount+0x143/0x1a0
>
> The problem is that rq_iter was never set, so the type is 0 (ie. ITER_UBUF)
> which causes user_backed_iter() to return true. The code doesn't
> malfunction because it checks the size of the iterator - which is 0.
>
> Fix cifs_get_num_sgs() to ignore rq_iter if its count is 0, thereby
> bypassing the warnings.
>
> It might be better to explicitly initialise rq_iter to a zero-length
> ITER_BVEC, say, as it can always be reinitialised later.
>
> Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
> Reported-by: Damian Tometzki <damian@...cv-rocks.de>
> Link: https://lore.kernel.org/r/ZUfQo47uo0p2ZsYg@fedora.fritz.box/
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Steve French <smfrench@...il.com>
> cc: Shyam Prasad N <sprasad@...rosoft.com>
> cc: Rohith Surabattula <rohiths.msft@...il.com>
> cc: Paulo Alcantara <pc@...guebit.com>
> cc: Namjae Jeon <linkinjeon@...nel.org>
> cc: Tom Talpey <tom@...pey.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: Eric Biggers <ebiggers@...nel.org>
> cc: linux-cifs@...r.kernel.org
> cc: linux-fsdevel@...r.kernel.org
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f1b4cb650b9a0eeba206d8f069fcdc532bfbcd74 [1]
> ---
> fs/smb/client/cifsglob.h | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
> index 02082621d8e0..c70760871606 100644
> --- a/fs/smb/client/cifsglob.h
> +++ b/fs/smb/client/cifsglob.h
> @@ -2143,6 +2143,7 @@ static inline int cifs_get_num_sgs(const struct smb_rqst *rqst,
> unsigned int len, skip;
> unsigned int nents = 0;
> unsigned long addr;
> + size_t data_size;
> int i, j;
>
> /*
> @@ -2158,17 +2159,21 @@ static inline int cifs_get_num_sgs(const struct smb_rqst *rqst,
> * rqst[1+].rq_iov[0+] data to be encrypted/decrypted
> */
> for (i = 0; i < num_rqst; i++) {
> + data_size = iov_iter_count(&rqst[i].rq_iter);
> +
> /* We really don't want a mixture of pinned and unpinned pages
> * in the sglist. It's hard to keep track of which is what.
> * Instead, we convert to a BVEC-type iterator higher up.
> */
> - if (WARN_ON_ONCE(user_backed_iter(&rqst[i].rq_iter)))
> + if (data_size &&
> + WARN_ON_ONCE(user_backed_iter(&rqst[i].rq_iter)))
> return -EIO;
>
> /* We also don't want to have any extra refs or pins to clean
> * up in the sglist.
> */
> - if (WARN_ON_ONCE(iov_iter_extract_will_pin(&rqst[i].rq_iter)))
> + if (data_size &&
> + WARN_ON_ONCE(iov_iter_extract_will_pin(&rqst[i].rq_iter)))
> return -EIO;
>
> for (j = 0; j < rqst[i].rq_nvec; j++) {
> @@ -2184,7 +2189,8 @@ static inline int cifs_get_num_sgs(const struct smb_rqst *rqst,
> }
> skip = 0;
> }
> - nents += iov_iter_npages(&rqst[i].rq_iter, INT_MAX);
> + if (data_size)
> + nents += iov_iter_npages(&rqst[i].rq_iter, INT_MAX);
> }
> nents += DIV_ROUND_UP(offset_in_page(sig) + SMB2_SIGNATURE_SIZE, PAGE_SIZE);
> return nents;
>
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