ovl: fix NULL pointer dereference in copy up warning

commit 4ee7e4a6c9b298da44029ed9ec8ed23ae49cc209 upstream.

This patch is fixing a NULL pointer dereference to get a recently
introduced warning m

ovl: fix NULL pointer dereference in copy up warning

commit 4ee7e4a6c9b298da44029ed9ec8ed23ae49cc209 upstream.

This patch is fixing a NULL pointer dereference to get a recently
introduced warning message working.

Fixes: 5b0a414d06c3 ("ovl: fix filattr copy-up failure")
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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ovl: don't fail copy up if no fileattr support on upper

commit 94fd19752b28aa66c98e7991734af91dfc529f8f upstream.

Christoph Fritz is reporting that failure to copy up fileattr when upper
doesn't su

ovl: don't fail copy up if no fileattr support on upper

commit 94fd19752b28aa66c98e7991734af91dfc529f8f upstream.

Christoph Fritz is reporting that failure to copy up fileattr when upper
doesn't support fileattr or xattr results in a regression.

Return success in these failure cases; this reverts overlayfs to the old
behavior.

Add a pr_warn_once() in these cases to still let the user know about the
copy up failures.

Reported-by: Christoph Fritz <chf.fritz@googlemail.com>
Fixes: 72db82115d2b ("ovl: copy up sync/noatime fileattr flags")
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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ovl: fix filattr copy-up failure

commit 5b0a414d06c3ed2097e32ef7944a4abb644b89bd upstream.

This regression can be reproduced with ntfs-3g and overlayfs:

mkdir lower upper work overlay
dd if=/d

ovl: fix filattr copy-up failure

commit 5b0a414d06c3ed2097e32ef7944a4abb644b89bd upstream.

This regression can be reproduced with ntfs-3g and overlayfs:

mkdir lower upper work overlay
dd if=/dev/zero of=ntfs.raw bs=1M count=2
mkntfs -F ntfs.raw
mount ntfs.raw lower
touch lower/file.txt
mount -t overlay -o lowerdir=lower,upperdir=upper,workdir=work - overlay
mv overlay/file.txt overlay/file2.txt

mv fails and (misleadingly) prints

mv: cannot move 'overlay/file.txt' to a subdirectory of itself, 'overlay/file2.txt'

The reason is that ovl_copy_fileattr() is triggered due to S_NOATIME being
set on all inodes (by fuse) regardless of fileattr.

ovl_copy_fileattr() tries to retrieve file attributes from lower file, but
that fails because filesystem does not support this ioctl (this should fail
with ENOTTY, but ntfs-3g return EINVAL instead). This failure is
propagated to origial operation (in this case rename) that triggered the
copy-up.

The fix is to ignore ENOTTY and EINVAL errors from fileattr_get() in copy
up. This also requires turning the internal ENOIOCTLCMD into ENOTTY.

As a further measure to prevent unnecessary failures, only try the
fileattr_get/set on upper if there are any flags to copy up.

Side note: a number of filesystems set S_NOATIME (and sometimes other inode
flags) irrespective of fileattr flags. This causes unnecessary calls
during copy up, which might lead to a performance issue, especially if
latency is high. To fix this, the kernel would need to differentiate
between the two cases. E.g. introduce SB_NOATIME_UPDATE, a per-sb variant
of S_NOATIME. SB_NOATIME doesn't work, because that's interpreted as
"filesystem doesn't store an atime attribute"

Reported-and-tested-by: Kevin Locke <kevin@kevinlocke.name>
Fixes: 72db82115d2b ("ovl: copy up sync/noatime fileattr flags")
Cc: <stable@vger.kernel.org> # v5.15
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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ovl: use kvalloc in xattr copy-up

Extended attributes are usually small, but could be up to 64k in size, so
use the most efficient method for doing the allocation.

Signed-off-by: Miklos Szeredi <ms

ovl: use kvalloc in xattr copy-up

Extended attributes are usually small, but could be up to 64k in size, so
use the most efficient method for doing the allocation.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: consistent behavior for immutable/append-only inodes

When a lower file has immutable/append-only fileattr flags, the behavior of
overlayfs post copy up is inconsistent.

Immediattely after copy

ovl: consistent behavior for immutable/append-only inodes

When a lower file has immutable/append-only fileattr flags, the behavior of
overlayfs post copy up is inconsistent.

Immediattely after copy up, ovl inode still has the S_IMMUTABLE/S_APPEND
inode flags copied from lower inode, so vfs code still treats the ovl inode
as immutable/append-only. After ovl inode evict or mount cycle, the ovl
inode does not have these inode flags anymore.

We cannot copy up the immutable and append-only fileattr flags, because
immutable/append-only inodes cannot be linked and because overlayfs will
not be able to set overlay.* xattr on the upper inodes.

Instead, if any of the fileattr flags of interest exist on the lower inode,
we store them in overlay.protattr xattr on the upper inode and we read the
flags from xattr on lookup and on fileattr_get().

This gives consistent behavior post copy up regardless of inode eviction
from cache.

When user sets new fileattr flags, we update or remove the overlay.protattr
xattr.

Storing immutable/append-only fileattr flags in an xattr instead of upper
fileattr also solves other non-standard behavior issues - overlayfs can now
copy up children of "ovl-immutable" directories and lower aliases of
"ovl-immutable" hardlinks.

Reported-by: Chengguang Xu <cgxu519@mykernel.net>
Link: https://lore.kernel.org/linux-unionfs/20201226104618.239739-1-cgxu519@mykernel.net/
Link: https://lore.kernel.org/linux-unionfs/20210210190334.1212210-5-amir73il@gmail.com/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: copy up sync/noatime fileattr flags

When a lower file has sync/noatime fileattr flags, the behavior of
overlayfs post copy up is inconsistent.

Immediately after copy up, ovl inode still has th

ovl: copy up sync/noatime fileattr flags

When a lower file has sync/noatime fileattr flags, the behavior of
overlayfs post copy up is inconsistent.

Immediately after copy up, ovl inode still has the S_SYNC/S_NOATIME
inode flags copied from lower inode, so vfs code still treats the ovl
inode as sync/noatime. After ovl inode evict or mount cycle,
the ovl inode does not have these inode flags anymore.

To fix this inconsistency, try to copy the fileattr flags on copy up
if the upper fs supports the fileattr_set() method.

This gives consistent behavior post copy up regardless of inode eviction
from cache.

We cannot copy up the immutable/append-only inode flags in a similar
manner, because immutable/append-only inodes cannot be linked and because
overlayfs will not be able to set overlay.* xattr on the upper inodes.

Those flags will be addressed by a followup patch.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: pass ovl_fs to ovl_check_setxattr()

Instead of passing the overlay dentry.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

ovl: fix missing revert_creds() on error path

Smatch complains about missing that the ovl_override_creds() doesn't
have a matching revert_creds() if the dentry is disconnected. Fix this
by moving t

ovl: fix missing revert_creds() on error path

Smatch complains about missing that the ovl_override_creds() doesn't
have a matching revert_creds() if the dentry is disconnected. Fix this
by moving the ovl_override_creds() until after the disconnected check.

Fixes: aa3ff3c152ff ("ovl: copy up of disconnected dentries")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

show more ...

ovl: skip getxattr of security labels

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listsecurity hooks to list the xattrs that LSMs will
intercept in in

ovl: skip getxattr of security labels

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listsecurity hooks to list the xattrs that LSMs will
intercept in inode_getxattr hooks.

When selinux LSM is installed but not initialized, it will list the
security.selinux xattr in inode_listsecurity, but will not intercept it
in inode_getxattr. This results in -ENODATA for a getxattr call for an
xattr returned by listxattr.

This situation was manifested as overlayfs failure to copy up lower
files from squashfs when selinux is built-in but not initialized,
because ovl_copy_xattr() iterates the lower inode xattrs by
vfs_listxattr() and vfs_getxattr().

ovl_copy_xattr() skips copy up of security labels that are indentified by
inode_copy_up_xattr LSM hooks, but it does that after vfs_getxattr().
Since we are not going to copy them, skip vfs_getxattr() of the security
labels.

Reported-by: Michael Labriola <michael.d.labriola@gmail.com>
Tested-by: Michael Labriola <michael.d.labriola@gmail.com>
Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@aldarion.sourceruckus.org/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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xattr: handle idmapped mounts

When interacting with extended attributes the vfs verifies that the
caller is privileged over the inode with which the extended attribute is
associated. For posix acces

xattr: handle idmapped mounts

When interacting with extended attributes the vfs verifies that the
caller is privileged over the inode with which the extended attribute is
associated. For posix access and posix default extended attributes a uid
or gid can be stored on-disk. Let the functions handle posix extended
attributes on idmapped mounts. If the inode is accessed through an
idmapped mount we need to map it according to the mount's user
namespace. Afterwards the checks are identical to non-idmapped mounts.
This has no effect for e.g. security xattrs since they don't store uids
or gids and don't perform permission checks on them like posix acls do.

Link: https://lore.kernel.org/r/20210121131959.646623-10-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

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attr: handle idmapped mounts

When file attributes are changed most filesystems rely on the
setattr_prepare(), setattr_copy(), and notify_change() helpers for
initialization and permission checking.

attr: handle idmapped mounts

When file attributes are changed most filesystems rely on the
setattr_prepare(), setattr_copy(), and notify_change() helpers for
initialization and permission checking. Let them handle idmapped mounts.
If the inode is accessed through an idmapped mount map it into the
mount's user namespace. Afterwards the checks are identical to
non-idmapped mounts. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Helpers that perform checks on the ia_uid and ia_gid fields in struct
iattr assume that ia_uid and ia_gid are intended values and have already
been mapped correctly at the userspace-kernelspace boundary as we
already do today. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-8-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

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ovl: do not fail when setting origin xattr

Comment above call already says this, but only EOPNOTSUPP is ignored, other
failures are not.

For example setting "user.*" will fail with EPERM on symlink

ovl: do not fail when setting origin xattr

Comment above call already says this, but only EOPNOTSUPP is ignored, other
failures are not.

For example setting "user.*" will fail with EPERM on symlink/special.

Ignore this error as well.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: introduce new "uuid=off" option for inodes index feature

This replaces uuid with null in overlayfs file handles and thus relaxes
uuid checks for overlay index feature. It is only possible in ca

ovl: introduce new "uuid=off" option for inodes index feature

This replaces uuid with null in overlayfs file handles and thus relaxes
uuid checks for overlay index feature. It is only possible in case there is
only one filesystem for all the work/upper/lower directories and bare file
handles from this backing filesystem are unique. In other case when we have
multiple filesystems lets just fallback to "uuid=on" which is and
equivalent of how it worked before with all uuid checks.

This is needed when overlayfs is/was mounted in a container with index
enabled (e.g.: to be able to resolve inotify watch file handles on it to
paths in CRIU), and this container is copied and started alongside with the
original one. This way the "copy" container can't have the same uuid on the
superblock and mounting the overlayfs from it later would fail.

That is an example of the problem on top of loop+ext4:

dd if=/dev/zero of=loopbackfile.img bs=100M count=10
losetup -fP loopbackfile.img
losetup -a
#/dev/loop0: [64768]:35 (/loop-test/loopbackfile.img)
mkfs.ext4 loopbackfile.img
mkdir loop-mp
mount -o loop /dev/loop0 loop-mp
mkdir loop-mp/{lower,upper,work,merged}
mount -t overlay overlay -oindex=on,lowerdir=loop-mp/lower,\
upperdir=loop-mp/upper,workdir=loop-mp/work loop-mp/merged
umount loop-mp/merged
umount loop-mp
e2fsck -f /dev/loop0
tune2fs -U random /dev/loop0

mount -o loop /dev/loop0 loop-mp
mount -t overlay overlay -oindex=on,lowerdir=loop-mp/lower,\
upperdir=loop-mp/upper,workdir=loop-mp/work loop-mp/merged
#mount: /loop-test/loop-mp/merged:
#mount(2) system call failed: Stale file handle.

If you just change the uuid of the backing filesystem, overlay is not
mounting any more. In Virtuozzo we copy container disks (ploops) when
create the copy of container and we require fs uuid to be unique for a new
container.

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: propagate ovl_fs to ovl_decode_real_fh and ovl_encode_real_fh

This will be used in next patch to be able to change uuid checks and add
uuid nullification based on ofs->config.index for a new "u

ovl: propagate ovl_fs to ovl_decode_real_fh and ovl_encode_real_fh

This will be used in next patch to be able to change uuid checks and add
uuid nullification based on ofs->config.index for a new "uuid=off" mode.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: fix missing revert_creds() on error path

commit 7b279bbfd2b230c7a210ff8f405799c7e46bbf48 upstream.

Smatch complains about missing that the ovl_override_creds() doesn't
have a matching revert_c

ovl: fix missing revert_creds() on error path

commit 7b279bbfd2b230c7a210ff8f405799c7e46bbf48 upstream.

Smatch complains about missing that the ovl_override_creds() doesn't
have a matching revert_creds() if the dentry is disconnected. Fix this
by moving the ovl_override_creds() until after the disconnected check.

Fixes: aa3ff3c152ff ("ovl: copy up of disconnected dentries")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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ovl: skip getxattr of security labels

[ Upstream commit 03fedf93593c82538b18476d8c4f0e8f8435ea70 ]

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listse

ovl: skip getxattr of security labels

[ Upstream commit 03fedf93593c82538b18476d8c4f0e8f8435ea70 ]

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listsecurity hooks to list the xattrs that LSMs will
intercept in inode_getxattr hooks.

When selinux LSM is installed but not initialized, it will list the
security.selinux xattr in inode_listsecurity, but will not intercept it
in inode_getxattr. This results in -ENODATA for a getxattr call for an
xattr returned by listxattr.

This situation was manifested as overlayfs failure to copy up lower
files from squashfs when selinux is built-in but not initialized,
because ovl_copy_xattr() iterates the lower inode xattrs by
vfs_listxattr() and vfs_getxattr().

ovl_copy_xattr() skips copy up of security labels that are indentified by
inode_copy_up_xattr LSM hooks, but it does that after vfs_getxattr().
Since we are not going to copy them, skip vfs_getxattr() of the security
labels.

Reported-by: Michael Labriola <michael.d.labriola@gmail.com>
Tested-by: Michael Labriola <michael.d.labriola@gmail.com>
Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@aldarion.sourceruckus.org/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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ovl: pass ovl_fs down to functions accessing private xattrs

This paves the way for optionally using the "user.overlay." xattr
namespace.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

ovl: drop flags argument from ovl_do_setxattr()

All callers pass zero flags to ovl_do_setxattr(). So drop this argument.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

ovl: adhere to the vfs_ vs. ovl_do_ conventions for xattrs

Call ovl_do_*xattr() when accessing an overlay private xattr, vfs_*xattr()
otherwise.

This has an effect on debug output, which is made mo

ovl: adhere to the vfs_ vs. ovl_do_ conventions for xattrs

Call ovl_do_*xattr() when accessing an overlay private xattr, vfs_*xattr()
otherwise.

This has an effect on debug output, which is made more consistent by this
patch.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: clean up ovl_getxattr() in copy_up.c

Lose the padding and the failure message (in line with other parts of the
copy up process). Return zero for both nonexistent or empty xattr.

Signed-off-by

ovl: clean up ovl_getxattr() in copy_up.c

Lose the padding and the failure message (in line with other parts of the
copy up process). Return zero for both nonexistent or empty xattr.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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duplicate ovl_getxattr()

ovl_getattr() returns the value of an xattr in a kmalloced buffer. There
are two callers:

ovl_copy_up_meta_inode_data() (copy_up.c)
ovl_get_redirect_xattr() (util.c)

Th

duplicate ovl_getxattr()

ovl_getattr() returns the value of an xattr in a kmalloced buffer. There
are two callers:

ovl_copy_up_meta_inode_data() (copy_up.c)
ovl_get_redirect_xattr() (util.c)

This patch just copies ovl_getxattr() to copy_up.c, the following patches
will deal with the differences in idividual callers.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: provide a mount option "volatile"

Container folks are complaining that dnf/yum issues too many sync while
installing packages and this slows down the image build. Build requirement
is such that

ovl: provide a mount option "volatile"

Container folks are complaining that dnf/yum issues too many sync while
installing packages and this slows down the image build. Build requirement
is such that they don't care if a node goes down while build was still
going on. In that case, they will simply throw away unfinished layer and
start new build. So they don't care about syncing intermediate state to the
disk and hence don't want to pay the price associated with sync.

So they are asking for mount options where they can disable sync on overlay
mount point.

They primarily seem to have two use cases.

- For building images, they will mount overlay with nosync and then sync
upper layer after unmounting overlay and reuse upper as lower for next
layer.

- For running containers, they don't seem to care about syncing upper layer
because if node goes down, they will simply throw away upper layer and
create a fresh one.

So this patch provides a mount option "volatile" which disables all forms
of sync. Now it is caller's responsibility to throw away upper if system
crashes or shuts down and start fresh.

With "volatile", I am seeing roughly 20% speed up in my VM where I am just
installing emacs in an image. Installation time drops from 31 seconds to 25
seconds when nosync option is used. This is for the case of building on top
of an image where all packages are already cached. That way I take out the
network operations latency out of the measurement.

Giuseppe is also looking to cut down on number of iops done on the disk. He
is complaining that often in cloud their VMs are throttled if they cross
the limit. This option can help them where they reduce number of iops (by
cutting down on frequent sync and writebacks).

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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treewide: Remove uninitialized_var() usage

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused vari

treewide: Remove uninitialized_var() usage

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.

In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:

git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
xargs perl -pi -e \
's/\buninitialized_var\(([^\)]+)\)/\1/g;
s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'

drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.

No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
alpha, and m68k.

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Reviewed-by: Leon Romanovsky <leonro@mellanox.com> # drivers/infiniband and mlx4/mlx5
Acked-by: Jason Gunthorpe <jgg@mellanox.com> # IB
Acked-by: Kalle Valo <kvalo@codeaurora.org> # wireless drivers
Reviewed-by: Chao Yu <yuchao0@huawei.com> # erofs
Signed-off-by: Kees Cook <keescook@chromium.org>

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ovl: change ovl_copy_up_flags static

"ovl_copy_up_flags" is used in copy_up.c.
so, change it static.

Signed-off-by: youngjun <her0gyugyu@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.co

ovl: change ovl_copy_up_flags static

"ovl_copy_up_flags" is used in copy_up.c.
so, change it static.

Signed-off-by: youngjun <her0gyugyu@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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ovl: initialize error in ovl_copy_xattr

In ovl_copy_xattr, if all the xattrs to be copied are overlayfs private
xattrs, the copy loop will terminate without assigning anything to the
error variable,

ovl: initialize error in ovl_copy_xattr

In ovl_copy_xattr, if all the xattrs to be copied are overlayfs private
xattrs, the copy loop will terminate without assigning anything to the
error variable, thus returning an uninitialized value.

If ovl_copy_xattr is called from ovl_clear_empty, this uninitialized error
value is put into a pointer by ERR_PTR(), causing potential invalid memory
accesses down the line.

This commit initialize error with 0. This is the correct value because when
there's no xattr to copy, because all xattrs are private, ovl_copy_xattr
should succeed.

This bug is discovered with the help of INIT_STACK_ALL and clang.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405
Fixes: 0956254a2d5b ("ovl: don't copy up opaqueness")
Cc: stable@vger.kernel.org # v4.8
Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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