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SubjectRe: [PATCH] tmpfs: Disallow CONFIG_TMPFS_INODE64 on s390
On Fri,  5 Feb 2021 17:06:20 -0600 Seth Forshee <seth.forshee@canonical.com> wrote:

> This feature requires ino_t be 64-bits, which is true for every
> 64-bit architecture but s390, so prevent this option from being
> selected there.
>

The previous patch nicely described the end-user impact of the bug.
This is especially important when requesting a -stable backport.

Here's what I ended up with:


From: Seth Forshee <seth.forshee@canonical.com>
Subject: tmpfs: disallow CONFIG_TMPFS_INODE64 on s390

Currently there is an assumption in tmpfs that 64-bit architectures also
have a 64-bit ino_t. This is not true on s390 which has a 32-bit ino_t.
With CONFIG_TMPFS_INODE64=y tmpfs mounts will get 64-bit inode numbers and
display "inode64" in the mount options, but passing the "inode64" mount
option will fail. This leads to the following behavior:

# mkdir mnt
# mount -t tmpfs nodev mnt
# mount -o remount,rw mnt
mount: /home/ubuntu/mnt: mount point not mounted or bad option.

As mount sees "inode64" in the mount options and thus passes it in the
options for the remount.


So prevent CONFIG_TMPFS_INODE64 from being selected on s390.

Link: https://lkml.kernel.org/r/20210205230620.518245-1-seth.forshee@canonical.com
Fixes: ea3271f7196c ("tmpfs: support 64-bit inums per-sb")
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: <stable@vger.kernel.org> [5.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

fs/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/Kconfig~tmpfs-disallow-config_tmpfs_inode64-on-s390
+++ a/fs/Kconfig
@@ -203,7 +203,7 @@ config TMPFS_XATTR

config TMPFS_INODE64
bool "Use 64-bit ino_t by default in tmpfs"
- depends on TMPFS && 64BIT
+ depends on TMPFS && 64BIT && !S390
default n
help
tmpfs has historically used only inode numbers as wide as an unsigned
_
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