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fuse: Fix VM_BUG_ON_PAGE issue while accessing zero ref count page
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There is a potential race between fuse_abort_conn() and
fuse_copy_page() as shown below, due to which VM_BUG_ON_PAGE
crash is observed for accessing a free page.

context#1:                      context#2:
fuse_dev_do_read()              fuse_abort_conn()
->fuse_copy_args()               ->end_requests()
 ->fuse_copy_pages()              ->request_end()
    ->fuse_copy_page()               ->fuse_writepage_end)
      ->fuse_ref_page()                ->fuse_writepage_free()
                                          ->__free_page()
					    ->put_page_testzero()

      ->get_page()
      ->VM_BUG_ON_PAGE()

This results in below crash as when ->put_page_testzero() in context#2
decrease the page reference and get_page() in context#1 accessed it
with zero page reference count.

[  174.391095]  (1)[10406:Thread-6]page dumped because:
VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))
[  174.391113]  (1)[10406:Thread-6]page allocated via order 0,
migratetype Unmovable, gfp_mask
0x620042(GFP_NOFS|__GFP_HIGHMEM|__GFP_HARDWALL), pid 261, ts
174390946312 ns

[  174.391135]  (1)[10406:Thread-6] prep_new_page+0x13c/0x210
[  174.391148]  (1)[10406:Thread-6] get_page_from_freelist+0x21ac/0x2370
[  174.391161]  (1)[10406:Thread-6] __alloc_pages_nodemask+0x244/0x14a8
[  174.391176]  (1)[10406:Thread-6] fuse_writepages_fill+0x150/0x708
[  174.391190]  (1)[10406:Thread-6] write_cache_pages+0x3d8/0x550
[  174.391202]  (1)[10406:Thread-6] fuse_writepages+0x94/0x130
[  174.391214]  (1)[10406:Thread-6] do_writepages+0x74/0x140
[  174.391228]  (1)[10406:Thread-6] __writeback_single_inode+0x168/0x788
[  174.391239]  (1)[10406:Thread-6] writeback_sb_inodes+0x56c/0xab8
[  174.391251]  (1)[10406:Thread-6] __writeback_inodes_wb+0x94/0x180
[  174.391262]  (1)[10406:Thread-6] wb_writeback+0x318/0x618
[  174.391274]  (1)[10406:Thread-6] wb_workfn+0x468/0x828
[  174.391290]  (1)[10406:Thread-6] process_one_work+0x3d0/0x720
[  174.391302]  (1)[10406:Thread-6] worker_thread+0x234/0x4c0
[  174.391314]  (1)[10406:Thread-6] kthread+0x144/0x158
[  174.391327]  (1)[10406:Thread-6] ret_from_fork+0x10/0x1c
[  174.391363]  (1)[10406:Thread-6]------------[ cut here ]------------
[  174.391371]  (1)[10406:Thread-6]kernel BUG at include/linux/mm.h:980!
[  174.391381]  (1)[10406:Thread-6]Internal error: Oops - BUG: 0 [#1]
...
[  174.486928]  (1)[10406:Thread-6]pc : fuse_copy_page+0x750/0x790
[  174.493029]  (1)[10406:Thread-6]lr : fuse_copy_page+0x750/0x790
[  174.718831]  (1)[10406:Thread-6] fuse_copy_page+0x750/0x790
[  174.718838]  (1)[10406:Thread-6] fuse_copy_args+0xb4/0x1e8
[  174.718843]  (1)[10406:Thread-6] fuse_dev_do_read+0x424/0x888
[  174.718848]  (1)[10406:Thread-6] fuse_dev_splice_read+0x94/0x200
[  174.718856]  (1)[10406:Thread-6] __arm64_sys_splice+0x874/0xb20
[  174.718864]  (1)[10406:Thread-6] el0_svc_common+0xc8/0x240
[  174.718869]  (1)[10406:Thread-6] el0_svc_handler+0x6c/0x88
[  174.718875]  (1)[10406:Thread-6] el0_svc+0x8/0xc
[  174.778853]  (1)[10406:Thread-6]Kernel panic - not syncing: Fatal

Fix this by protecting fuse_ref_page() with the same fc->lock as in
fuse_abort_conn().

Changes since V2:
- Moved the spin lock from fuse_copy_pages() to fuse_ref_page()

Changes since V1:
- Modified the logic as per kernel v5.9-rc1.
- Added Reported by tag.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Pradeep P V K <ppvk@codeaurora.org>
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@intel-lab-lkp
Pradeep P V K authored and intel-lab-lkp committed Sep 7, 2020
1 parent ddca99b commit f99df00
Showing 1 changed file with 14 additions and 12 deletions.
26 changes: 14 additions & 12 deletions fs/fuse/dev.c
View file
Expand Up @@ -875,14 +875,15 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
}

static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page,
unsigned offset, unsigned count)
unsigned offset, unsigned count, struct fuse_conn *fc)
{
struct pipe_buffer *buf;
int err;

if (cs->nr_segs >= cs->pipe->max_usage)
return -EIO;

spin_lock(&fc->lock);
err = unlock_request(cs->req);
if (err)
return err;
Expand All @@ -892,6 +893,7 @@ static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page,
buf = cs->pipebufs;
get_page(page);
buf->page = page;
spin_unlock(&fc->lock);
buf->offset = offset;
buf->len = count;

Expand All @@ -907,7 +909,7 @@ static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page,
* done atomically
*/
static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep,
unsigned offset, unsigned count, int zeroing)
unsigned offset, unsigned count, int zeroing, struct fuse_conn *fc)
{
int err;
struct page *page = *pagep;
Expand All @@ -917,7 +919,7 @@ static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep,

while (count) {
if (cs->write && cs->pipebufs && page) {
return fuse_ref_page(cs, page, offset, count);
return fuse_ref_page(cs, page, offset, count, fc);
} else if (!cs->len) {
if (cs->move_pages && page &&
offset == 0 && count == PAGE_SIZE) {
Expand Down Expand Up @@ -945,7 +947,7 @@ static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep,

/* Copy pages in the request to/from userspace buffer */
static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
int zeroing)
int zeroing, struct fuse_conn *fc)
{
unsigned i;
struct fuse_req *req = cs->req;
Expand All @@ -957,7 +959,7 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
unsigned int offset = ap->descs[i].offset;
unsigned int count = min(nbytes, ap->descs[i].length);

err = fuse_copy_page(cs, &ap->pages[i], offset, count, zeroing);
err = fuse_copy_page(cs, &ap->pages[i], offset, count, zeroing, fc);
if (err)
return err;

Expand All @@ -983,15 +985,15 @@ static int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
/* Copy request arguments to/from userspace buffer */
static int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
unsigned argpages, struct fuse_arg *args,
int zeroing)
int zeroing, struct fuse_conn *fc)
{
int err = 0;
unsigned i;

for (i = 0; !err && i < numargs; i++) {
struct fuse_arg *arg = &args[i];
if (i == numargs - 1 && argpages)
err = fuse_copy_pages(cs, arg->size, zeroing);
err = fuse_copy_pages(cs, arg->size, zeroing, fc);
else
err = fuse_copy_one(cs, arg->value, arg->size);
}
Expand Down Expand Up @@ -1260,7 +1262,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
err = fuse_copy_one(cs, &req->in.h, sizeof(req->in.h));
if (!err)
err = fuse_copy_args(cs, args->in_numargs, args->in_pages,
(struct fuse_arg *) args->in_args, 0);
(struct fuse_arg *) args->in_args, 0, fc);
fuse_copy_finish(cs);
spin_lock(&fpq->lock);
clear_bit(FR_LOCKED, &req->flags);
Expand Down Expand Up @@ -1590,7 +1592,7 @@ static int fuse_notify_store(struct fuse_conn *fc, unsigned int size,
goto out_iput;

this_num = min_t(unsigned, num, PAGE_SIZE - offset);
err = fuse_copy_page(cs, &page, offset, this_num, 0);
err = fuse_copy_page(cs, &page, offset, this_num, 0, fc);
if (!err && offset == 0 &&
(this_num == PAGE_SIZE || file_size == end))
SetPageUptodate(page);
Expand Down Expand Up @@ -1792,7 +1794,7 @@ static struct fuse_req *request_find(struct fuse_pqueue *fpq, u64 unique)
}

static int copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
unsigned nbytes)
unsigned nbytes, struct fuse_conn *fc)
{
unsigned reqsize = sizeof(struct fuse_out_header);

Expand All @@ -1809,7 +1811,7 @@ static int copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
lastarg->size -= diffsize;
}
return fuse_copy_args(cs, args->out_numargs, args->out_pages,
args->out_args, args->page_zeroing);
args->out_args, args->page_zeroing, fc);
}

/*
Expand Down Expand Up @@ -1894,7 +1896,7 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
if (oh.error)
err = nbytes != sizeof(oh) ? -EINVAL : 0;
else
err = copy_out_args(cs, req->args, nbytes);
err = copy_out_args(cs, req->args, nbytes, fc);
fuse_copy_finish(cs);

spin_lock(&fpq->lock);
Expand Down

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