[Bug 2133182] [NEW] NFS EACCES regression in 6.15.4

Public bug reported:

Hi, up to the 6.15.2 mainline kernel, these commands correctly returned
EROFS (Read-only file system):

/usr/lib/klibc/bin/nfsmount -o ro 192.168.67.1:/srv/ltsp /mnt
true <>/mnt/some-existing-file
bash: /mnt/some-existing-file: Read-only file system

Strace says the respective call and result is:
openat(AT_FDCWD, "/mnt/some-existing-file", O_RDWR|O_CREAT, 0666) = -1 EROFS (Read-only file system)

Since 6.15.4 mainline kernel, they started incorrectly returning EACCES
instead:

bash: /mnt/some-existing-file: Permission denied
openat(AT_FDCWD, "/mnt/some-existing-file", O_RDWR|O_CREAT, 0666) = -1 EACCES (Permission denied)

This breaks for example the klibc losetup command, which in turn breaks
e.g. netbooting in certain cases:

/usr/lib/klibc/bin/losetup -f /mnt/some-existing-file
Permission denied

Looking at https://kernel.ubuntu.com/mainline/v6.15.4/CHANGES, I wonder if it's related to this change:
nfs: clear SB_RDONLY before getting superblock

** Affects: linux (Ubuntu)
Importance: Undecided
Status: New

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https://bugs.launchpad.net/bugs/2133182

Title:
NFS EACCES regression in 6.15.4

Status in linux package in Ubuntu:
New

Bug description:
Hi, up to the 6.15.2 mainline kernel, these commands correctly
returned EROFS (Read-only file system):

/usr/lib/klibc/bin/nfsmount -o ro 192.168.67.1:/srv/ltsp /mnt
true <>/mnt/some-existing-file
bash: /mnt/some-existing-file: Read-only file system

Strace says the respective call and result is:
openat(AT_FDCWD, "/mnt/some-existing-file", O_RDWR|O_CREAT, 0666) = -1 EROFS (Read-only file system)

Since 6.15.4 mainline kernel, they started incorrectly returning
EACCES instead:

bash: /mnt/some-existing-file: Permission denied
openat(AT_FDCWD, "/mnt/some-existing-file", O_RDWR|O_CREAT, 0666) = -1 EACCES (Permission denied)

This breaks for example the klibc losetup command, which in turn
breaks e.g. netbooting in certain cases:

/usr/lib/klibc/bin/losetup -f /mnt/some-existing-file
Permission denied

Looking at https://kernel.ubuntu.com/mainline/v6.15.4/CHANGES, I wonder if it's related to this change:
nfs: clear SB_RDONLY before getting superblock

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