it's almost always equal to current_fsuid(), but there's an exception -
if the first writeback fid is opened by non-root *and* that happens before
root has done any lookups in /, we end up doing attach for root. The
current code leaves the resulting FID owned by root from the server POV
and by non-root from the client one. Unfortunately, it means that e.g.
massive dcache eviction will leave that user buggered - they'll end
up redoing walks from / *and* picking that FID every time. As soon as
they try to create something, the things will get nasty.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We check if ->ki_pos is positive. However, by that point we have
already done rw_verify_area(), which would have rejected such
unless the file had been one of /dev/mem, /dev/kmem and /proc/kcore.
All of which do not have vectored rw methods, so we would've bailed
out even earlier.
This check had been introduced before rw_verify_area() had been added there
- in fact, it was a subset of checks done on sync paths by rw_verify_area()
(back then the /dev/mem exception didn't exist at all). The rest of checks
(mandatory locking, etc.) hadn't been added until later. Unfortunately,
by the time the call of rw_verify_area() got added, the /dev/mem exception
had already appeared, so it wasn't obvious that the older explicit check
downstream had become dead code. It *is* a dead code, though, since the few
files for which the exception applies do not have ->aio_{read,write}() or
->{read,write}_iter() and for them we won't reach that check anyway.
What's more, even if we ever introduce vectored methods for /dev/mem
and friends, they'll have to cope with negative positions anyway, since
readv(2) and writev(2) are using the same checks as read(2) and write(2) -
i.e. rw_verify_area().
Let's bury it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Way, way back kiocb used to be picked from arrays, so ioctx_alloc()
checked for multiplication overflow when calculating the size of
such array. By the time fs/aio.c went into the tree (in 2002) they
were already allocated one-by-one by kmem_cache_alloc(), so that
check had already become pointless. Let's bury it...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
unfortunately, allowing an arbitrary 16bit value means a possibility of
overflow in the calculation of total number of pages in bio_map_user_iov() -
we rely on there being no more than PAGE_SIZE members of sum in the
first loop there. If that sum wraps around, we end up allocating
too small array of pointers to pages and it's easy to overflow it in
the second loop.
X-Coverup: TINC (and there's no lumber cartel either)
Cc: stable@vger.kernel.org # way, way back
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We don't need req in either of those. We don't need nr_segs in caller.
We don't really need len in caller either - iov_iter_count(&iter) will do.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
the only non-trivial detail is that we do it before rw_verify_area(),
so we'd better cap the length ourselves in aio_setup_single_rw()
case (for vectored case rw_copy_check_uvector() will do that for us).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We have observed a BUG() crash in fs/attr.c:notify_change(). The crash
occurs during an rsync into a filesystem that is exported via NFS.
1.) fs/attr.c:notify_change() modifies the caller's version of attr.
2.) 6de0ec00ba ("VFS: make notify_change pass ATTR_KILL_S*ID to
setattr operations") introduced a BUG() restriction such that "no
function will ever call notify_change() with both ATTR_MODE and
ATTR_KILL_S*ID set". Under some circumstances though, it will have
assisted in setting the caller's version of attr to this very
combination.
3.) 27ac0ffeac ("locks: break delegations on any attribute
modification") introduced code to handle breaking
delegations. This can result in notify_change() being re-called. attr
_must_ be explicitly reset to avoid triggering the BUG() established
in #2.
4.) The path that that triggers this is via fs/open.c:chmod_common().
The combination of attr flags set here and in the first call to
notify_change() along with a later failed break_deleg_wait()
results in notify_change() being called again via retry_deleg
without resetting attr.
Solution is to move retry_deleg in chmod_common() a bit further up to
ensure attr is completely reset.
There are other places where this seemingly could occur, such as
fs/utimes.c:utimes_common(), but the attr flags are not initially
set in such a way to trigger this.
Fixes: 27ac0ffeac ("locks: break delegations on any attribute modification")
Reported-by: Eric Meddaugh <etmsys@rit.edu>
Tested-by: Eric Meddaugh <etmsys@rit.edu>
Signed-off-by: Andrew Elble <aweits@rit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
On a distributed filesystem it's possible for lookup to discover that a
directory it just found is already cached elsewhere in the directory
heirarchy. The dcache won't let us keep the directory in both places,
so we have to move the dentry to the new location from the place we
previously had it cached.
If the parent has changed, then this requires all the same locks as we'd
need to do a cross-directory rename. But we're already in lookup
holding one parent's i_mutex, so it's too late to acquire those locks in
the right order.
The (unreliable) solution in __d_unalias is to trylock() the required
locks and return -EBUSY if it fails.
I see no particular reason for returning -EBUSY, and -ESTALE is already
the result of some other lookup races on NFS. I think -ESTALE is the
more helpful error return. It also allows us to take advantage of the
logic Jeff Layton added in c6a9428401 "vfs: fix renameat to retry on
ESTALE errors" and ancestors, which hopefully resolves some of these
errors before they're returned to userspace.
I can reproduce these cases using NFS with:
ssh root@$client '
mount -olookupcache=pos '$server':'$export' /mnt/
mkdir /mnt/TO
mkdir /mnt/DIR
touch /mnt/DIR/test.txt
while true; do
strace -e open cat /mnt/DIR/test.txt 2>&1 | grep EBUSY
done
'
ssh root@$server '
while true; do
mv $export/DIR $export/TO/DIR
mv $export/TO/DIR $export/DIR
done
'
It also helps to add some other concurrent use of the directory on the
client (e.g., "ls /mnt/TO"). And you can replace the server-side mv's
by client-side mv's that are repeatedly killed. (If the client is
interrupted while waiting for the RENAME response then it's left with a
dentry that has to go under one parent or the other, but it doesn't yet
know which.)
Acked-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
simillar to iov_iter_fault_in_readable() but differs in that it is
not limited to faulting in the first iovec and instead faults in
"bytes" bytes iterating over the iovecs as necessary.
Also, instead of only faulting in the first and last page of the
range, all pages are faulted in.
This function is needed by NTFS when it does multi page file
writes.
Signed-off-by: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
For one thing, LOOKUP_DIRECTORY will be dealt with in do_last().
For another, name can be an empty string, but not NULL - no callers
pass that and it would oops immediately if they would.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
flush_old_exec() has already done that. Back on 2011 a bunch of
instances like that had been kicked out, but that hadn't taken
care of then-out-of-tree architectures, obviously, and they served
as reinfection vector...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
just make const char iname[] the last member and compare name->name with
name->iname instead of checking name->separate
We need to make sure that out-of-line name doesn't end up allocated adjacent
to struct filename refering to it; fortunately, it's easy to achieve - just
allocate that struct filename with one byte in ->iname[], so that ->iname[0]
will be inside the same object and thus have an address different from that
of out-of-line name [spotted by Boqun Feng <boqun.feng@gmail.com>]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
For kernel_sendmsg() that eliminates the need to play with setfs();
for kernel_recvmsg() it does *not* - a couple of callers are using
it with non-NULL ->msg_control, which would be treated as userland
address on recvmsg side of things.
In all cases we are really setting a kvec-backed iov_iter, though.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
