ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 113 insertions, 0 deletions

diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
new file mode 100644
index 000000000..5f1f969f4
--- /dev/null
+++ b/fs/udf/ialloc.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ialloc.c
+ *
+ * PURPOSE
+ *	Inode allocation handling routines for the OSTA-UDF(tm) filesystem.
+ *
+ * COPYRIGHT
+ *  (C) 1998-2001 Ben Fennema
+ *
+ * HISTORY
+ *
+ *  02/24/99 blf  Created.
+ *
+ */
+
+#include "udfdecl.h"
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+
+#include "udf_i.h"
+#include "udf_sb.h"
+
+void udf_free_inode(struct inode *inode)
+{
+	udf_free_blocks(inode->i_sb, NULL, &UDF_I(inode)->i_location, 0, 1);
+}
+
+struct inode *udf_new_inode(struct inode *dir, umode_t mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct udf_sb_info *sbi = UDF_SB(sb);
+	struct inode *inode;
+	udf_pblk_t block;
+	uint32_t start = UDF_I(dir)->i_location.logicalBlockNum;
+	struct udf_inode_info *iinfo;
+	struct udf_inode_info *dinfo = UDF_I(dir);
+	int err;
+
+	inode = new_inode(sb);
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	iinfo = UDF_I(inode);
+	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
+		iinfo->i_efe = 1;
+		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
+			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
+		iinfo->i_data = kzalloc(inode->i_sb->s_blocksize -
+					sizeof(struct extendedFileEntry),
+					GFP_KERNEL);
+	} else {
+		iinfo->i_efe = 0;
+		iinfo->i_data = kzalloc(inode->i_sb->s_blocksize -
+					sizeof(struct fileEntry),
+					GFP_KERNEL);
+	}
+	if (!iinfo->i_data) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	err = -ENOSPC;
+	block = udf_new_block(dir->i_sb, NULL,
+			      dinfo->i_location.partitionReferenceNum,
+			      start, &err);
+	if (err) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(err);
+	}
+
+	iinfo->i_unique = lvid_get_unique_id(sb);
+	inode->i_generation = iinfo->i_unique;
+
+	inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_UID_SET))
+		inode->i_uid = sbi->s_uid;
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_GID_SET))
+		inode->i_gid = sbi->s_gid;
+
+	iinfo->i_location.logicalBlockNum = block;
+	iinfo->i_location.partitionReferenceNum =
+				dinfo->i_location.partitionReferenceNum;
+	inode->i_ino = udf_get_lb_pblock(sb, &iinfo->i_location, 0);
+	inode->i_blocks = 0;
+	iinfo->i_lenEAttr = 0;
+	iinfo->i_lenAlloc = 0;
+	iinfo->i_use = 0;
+	iinfo->i_checkpoint = 1;
+	iinfo->i_extraPerms = FE_PERM_U_CHATTR;
+	udf_update_extra_perms(inode, mode);
+
+	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
+	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_SHORT;
+	else
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_LONG;
+	simple_inode_init_ts(inode);
+	iinfo->i_crtime = inode_get_mtime(inode);
+	if (unlikely(insert_inode_locked(inode) < 0)) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(-EIO);
+	}
+	mark_inode_dirty(inode);
+
+	return inode;
+}