Re: [PATCH] cifs: Fix encryption of cleared, but unset rq_iter data buffers

Steve French
2023-11-07T18:51:40Z

cleaned up some minor whitespace warnings in the patch, added
Tested-by and Cc: stable and pushed to cifs-2.6.git for-next

On Mon, Nov 6, 2023 at 11:18 PM Damian Tometzki <damian@riscv-rocks.de> wrote:
>
> 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@riscv-rocks.de>
> > Link: https://lore.kernel.org/r/ZUfQo47uo0p2ZsYg@fedora.fritz.box/
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > cc: Steve French <smfrench@gmail.com>
> > cc: Shyam Prasad N <sprasad@microsoft.com>
> > cc: Rohith Surabattula <rohiths.msft@gmail.com>
> > cc: Paulo Alcantara <pc@manguebit.com>
> > cc: Namjae Jeon <linkinjeon@kernel.org>
> > cc: Tom Talpey <tom@talpey.com>
> > cc: Jeff Layton <jlayton@kernel.org>
> > cc: Eric Biggers <ebiggers@kernel.org>
> > cc: linux-cifs@vger.kernel.org
> > cc: linux-fsdevel@vger.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;
> >

--
Thanks,

Steve