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Linux: Fix zfs_prune panics v2 #17121

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Linux: Fix zfs_prune panics v2 #17121

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19 changes: 19 additions & 0 deletions config/kernel-sb-dying.m4
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
dnl #
dnl # SB_DYING exists since Linux 6.6
dnl #
AC_DEFUN([ZFS_AC_KERNEL_SRC_SB_DYING], [
ZFS_LINUX_TEST_SRC([sb_dying], [
#include <linux/fs.h>
],[
(void) SB_DYING;
])
])

AC_DEFUN([ZFS_AC_KERNEL_SB_DYING], [
AC_MSG_CHECKING([whether SB_DYING is defined])
ZFS_LINUX_TEST_RESULT([sb_dying], [
AC_MSG_RESULT(yes)
],[
AC_MSG_RESULT(no)
])
])
2 changes: 2 additions & 0 deletions config/kernel.m4
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
ZFS_AC_KERNEL_SRC_TRUNCATE_SETSIZE
ZFS_AC_KERNEL_SRC_SECURITY_INODE
ZFS_AC_KERNEL_SRC_FST_MOUNT
ZFS_AC_KERNEL_SRC_SB_DYING
ZFS_AC_KERNEL_SRC_SET_NLINK
ZFS_AC_KERNEL_SRC_SGET
ZFS_AC_KERNEL_SRC_VFS_FILEMAP_DIRTY_FOLIO
Expand Down Expand Up @@ -184,6 +185,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
ZFS_AC_KERNEL_TRUNCATE_SETSIZE
ZFS_AC_KERNEL_SECURITY_INODE
ZFS_AC_KERNEL_FST_MOUNT
ZFS_AC_KERNEL_SB_DYING
ZFS_AC_KERNEL_SET_NLINK
ZFS_AC_KERNEL_SGET
ZFS_AC_KERNEL_VFS_FILEMAP_DIRTY_FOLIO
Expand Down
26 changes: 17 additions & 9 deletions module/os/linux/zfs/zpl_super.c
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Original file line number Diff line number Diff line change
Expand Up @@ -376,17 +376,25 @@ zpl_prune_sb(uint64_t nr_to_scan, void *arg)
int objects = 0;

/*
* deactivate_locked_super calls shrinker_free and only then
* sops->kill_sb cb, resulting in UAF on umount when trying to reach
* for the shrinker functions in zpl_prune_sb of in-umount dataset.
* Increment if s_active is not zero, but don't prune if it is -
* umount could be underway.
* Ensure the superblock is not in the process of being torn down.
*/
if (atomic_inc_not_zero(&sb->s_active)) {
(void) -zfs_prune(sb, nr_to_scan, &objects);
atomic_dec(&sb->s_active);
#ifdef HAVE_SB_DYING
if (down_read_trylock(&sb->s_umount)) {
if (!(sb->s_flags & SB_DYING) && sb->s_root &&
(sb->s_flags & SB_BORN)) {
(void) zfs_prune(sb, nr_to_scan, &objects);
}
up_read(&sb->s_umount);
}

#else
if (down_read_trylock(&sb->s_umount)) {
if (!hlist_unhashed(&sb->s_instances) &&
sb->s_root && (sb->s_flags & SB_BORN)) {
(void) zfs_prune(sb, nr_to_scan, &objects);
}
up_read(&sb->s_umount);
}
#endif
}

const struct super_operations zpl_super_operations = {
Expand Down
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