From 1039bffd6ae9c75b42b7d148d6c1106134107b66 Mon Sep 17 00:00:00 2001 From: Xie Yuanbin Date: Tue, 28 Jul 2026 03:16:42 +0100 Subject: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults 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 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) Reviewed-by: Linus Walleij Signed-off-by: Qi Xi Signed-off-by: Xie Yuanbin Signed-off-by: Russell King --- net/ceph/buffer.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 net/ceph/buffer.c (limited to 'net/ceph/buffer.c') diff --git a/net/ceph/buffer.c b/net/ceph/buffer.c new file mode 100644 index 000000000..98c2ac438 --- /dev/null +++ b/net/ceph/buffer.c @@ -0,0 +1,59 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include + +#include +#include + +#include +#include +#include /* for kvmalloc */ + +struct ceph_buffer *ceph_buffer_new(size_t len, gfp_t gfp) +{ + struct ceph_buffer *b; + + b = kmalloc_obj(*b, gfp); + if (!b) + return NULL; + + b->vec.iov_base = kvmalloc(len, gfp); + if (!b->vec.iov_base) { + kfree(b); + return NULL; + } + + kref_init(&b->kref); + b->alloc_len = len; + b->vec.iov_len = len; + dout("buffer_new %p\n", b); + return b; +} +EXPORT_SYMBOL(ceph_buffer_new); + +void ceph_buffer_release(struct kref *kref) +{ + struct ceph_buffer *b = container_of(kref, struct ceph_buffer, kref); + + dout("buffer_release %p\n", b); + kvfree(b->vec.iov_base); + kfree(b); +} +EXPORT_SYMBOL(ceph_buffer_release); + +int ceph_decode_buffer(struct ceph_buffer **b, void **p, void *end) +{ + size_t len; + + ceph_decode_need(p, end, sizeof(u32), bad); + len = ceph_decode_32(p); + dout("decode_buffer len %d\n", (int)len); + ceph_decode_need(p, end, len, bad); + *b = ceph_buffer_new(len, GFP_NOFS); + if (!*b) + return -ENOMEM; + ceph_decode_copy(p, (*b)->vec.iov_base, len); + return 0; +bad: + return -EINVAL; +} -- cgit v1.3.1