The patch titled
Subject: fs/proc/vmcore: disallow vmcore modifications while the vmcore is open
has been added to the -mm mm-unstable branch. Its filename is
fs-proc-vmcore-disallow-vmcore-modifications-while-the-vmcore-is-open.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-vmcore-disallow-vmcore-modifications-while-the-vmcore-is-open.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: fs/proc/vmcore: disallow vmcore modifications while the vmcore is open
Date: Wed, 4 Dec 2024 13:54:34 +0100
The vmcoredd_update_size() call and its effects (size/offset changes) are
currently completely unsynchronized, and will cause trouble when performed
concurrently, or when done while someone is already reading the vmcore.
Let's protect all vmcore modifications by the vmcore_mutex, disallow
vmcore modifications while the vmcore is open, and warn on vmcore
modifications after the vmcore was already opened once: modifications
while the vmcore is open are unsafe, and modifications after the vmcore
was opened indicates trouble. Properly synchronize against concurrent
opening of the vmcore.
No need to grab the mutex during mmap()/read(): after we opened the
vmcore, modifications are impossible.
It's worth noting that modifications after the vmcore was opened are
completely unexpected, so failing if open, and warning if already opened
(+closed again) is good enough.
This change not only handles concurrent adding of device dumps +
concurrent reading of the vmcore properly, it also prepares for other
mechanisms that will modify the vmcore.
Link: https://lkml.kernel.org/r/20241204125444.1734652-4-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Eric Farman <farman@xxxxxxxxxxxxx>
Cc: Eugenio Pérez <eperezma@xxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Janosch Frank <frankja@xxxxxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Thomas Huth <thuth@xxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/vmcore.c | 57 ++++++++++++++++++++++++++-------------------
1 file changed, 34 insertions(+), 23 deletions(-)
--- a/fs/proc/vmcore.c~fs-proc-vmcore-disallow-vmcore-modifications-while-the-vmcore-is-open
+++ a/fs/proc/vmcore.c
@@ -68,6 +68,8 @@ DEFINE_STATIC_SRCU(vmcore_cb_srcu);
static LIST_HEAD(vmcore_cb_list);
/* Whether the vmcore has been opened once. */
static bool vmcore_opened;
+/* Whether the vmcore is currently open. */
+static unsigned int vmcore_open;
void register_vmcore_cb(struct vmcore_cb *cb)
{
@@ -122,6 +124,20 @@ static int open_vmcore(struct inode *ino
{
mutex_lock(&vmcore_mutex);
vmcore_opened = true;
+ if (vmcore_open + 1 == 0) {
+ mutex_unlock(&vmcore_mutex);
+ return -EBUSY;
+ }
+ vmcore_open++;
+ mutex_unlock(&vmcore_mutex);
+
+ return 0;
+}
+
+static int release_vmcore(struct inode *inode, struct file *file)
+{
+ mutex_lock(&vmcore_mutex);
+ vmcore_open--;
mutex_unlock(&vmcore_mutex);
return 0;
@@ -243,33 +259,27 @@ static int vmcoredd_copy_dumps(struct io
{
struct vmcoredd_node *dump;
u64 offset = 0;
- int ret = 0;
size_t tsz;
char *buf;
- mutex_lock(&vmcore_mutex);
list_for_each_entry(dump, &vmcoredd_list, list) {
if (start < offset + dump->size) {
tsz = min(offset + (u64)dump->size - start, (u64)size);
buf = dump->buf + start - offset;
- if (copy_to_iter(buf, tsz, iter) < tsz) {
- ret = -EFAULT;
- goto out_unlock;
- }
+ if (copy_to_iter(buf, tsz, iter) < tsz)
+ return -EFAULT;
size -= tsz;
start += tsz;
/* Leave now if buffer filled already */
if (!size)
- goto out_unlock;
+ return 0;
}
offset += dump->size;
}
-out_unlock:
- mutex_unlock(&vmcore_mutex);
- return ret;
+ return 0;
}
#ifdef CONFIG_MMU
@@ -278,20 +288,16 @@ static int vmcoredd_mmap_dumps(struct vm
{
struct vmcoredd_node *dump;
u64 offset = 0;
- int ret = 0;
size_t tsz;
char *buf;
- mutex_lock(&vmcore_mutex);
list_for_each_entry(dump, &vmcoredd_list, list) {
if (start < offset + dump->size) {
tsz = min(offset + (u64)dump->size - start, (u64)size);
buf = dump->buf + start - offset;
if (remap_vmalloc_range_partial(vma, dst, buf, 0,
- tsz)) {
- ret = -EFAULT;
- goto out_unlock;
- }
+ tsz))
+ return -EFAULT;
size -= tsz;
start += tsz;
@@ -299,14 +305,12 @@ static int vmcoredd_mmap_dumps(struct vm
/* Leave now if buffer filled already */
if (!size)
- goto out_unlock;
+ return 0;
}
offset += dump->size;
}
-out_unlock:
- mutex_unlock(&vmcore_mutex);
- return ret;
+ return 0;
}
#endif /* CONFIG_MMU */
#endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
@@ -691,6 +695,7 @@ static int mmap_vmcore(struct file *file
static const struct proc_ops vmcore_proc_ops = {
.proc_open = open_vmcore,
+ .proc_release = release_vmcore,
.proc_read_iter = read_vmcore,
.proc_lseek = default_llseek,
.proc_mmap = mmap_vmcore,
@@ -1516,12 +1521,18 @@ int vmcore_add_device_dump(struct vmcore
dump->buf = buf;
dump->size = data_size;
- /* Add the dump to driver sysfs list */
+ /* Add the dump to driver sysfs list and update the elfcore hdr */
mutex_lock(&vmcore_mutex);
- list_add_tail(&dump->list, &vmcoredd_list);
- mutex_unlock(&vmcore_mutex);
+ if (vmcore_opened)
+ pr_warn_once("Unexpected adding of device dump\n");
+ if (vmcore_open) {
+ ret = -EBUSY;
+ goto out_err;
+ }
+ list_add_tail(&dump->list, &vmcoredd_list);
vmcoredd_update_size(data_size);
+ mutex_unlock(&vmcore_mutex);
return 0;
out_err:
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm.patch
mm-filemap-dont-call-folio_test_locked-without-a-reference-in-next_uptodate_folio.patch
docs-tmpfs-update-the-large-folios-policy-for-tmpfs-and-shmem.patch
mm-memory_hotplug-move-debug_pagealloc_map_pages-into-online_pages_range.patch
mm-page_isolation-dont-pass-gfp-flags-to-isolate_single_pageblock.patch
mm-page_isolation-dont-pass-gfp-flags-to-start_isolate_page_range.patch
mm-page_alloc-make-__alloc_contig_migrate_range-static.patch
mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch
mm-page_alloc-forward-the-gfp-flags-from-alloc_contig_range-to-post_alloc_hook.patch
powernv-memtrace-use-__gfp_zero-with-alloc_contig_pages.patch
mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork.patch
fs-proc-vmcore-convert-vmcore_cb_lock-into-vmcore_mutex.patch
fs-proc-vmcore-replace-vmcoredd_mutex-by-vmcore_mutex.patch
fs-proc-vmcore-disallow-vmcore-modifications-while-the-vmcore-is-open.patch
fs-proc-vmcore-prefix-all-pr_-with-vmcore.patch
fs-proc-vmcore-move-vmcore-definitions-out-of-kcoreh.patch
fs-proc-vmcore-factor-out-allocating-a-vmcore-range-and-adding-it-to-a-list.patch
fs-proc-vmcore-factor-out-freeing-a-list-of-vmcore-ranges.patch
fs-proc-vmcore-introduce-proc_vmcore_device_ram-to-detect-device-ram-ranges-in-2nd-kernel.patch
virtio-mem-mark-device-ready-before-registering-callbacks-in-kdump-mode.patch
virtio-mem-remember-usable-region-size.patch
virtio-mem-support-config_proc_vmcore_device_ram.patch
s390-kdump-virtio-mem-kdump-support-config_proc_vmcore_device_ram.patch
