[PATCH 5.9 250/252] mm: fix readahead_page_batch for retry entries

Greg Kroah-Hartman
2020-11-23T13:00:13Z

From: Matthew Wilcox (Oracle) <willy@infradead.org>

commit 4349a83a3190c1d4414371161b0f4a4c3ccd3f9d upstream.

Both btrfs and fuse have reported faults caused by seeing a retry entry
instead of the page they were looking for. This was caused by a missing
check in the iterator.

As can be seen in the below panic log, the accessing 0x402 causes a
panic. In the xarray.h, 0x402 means RETRY_ENTRY.

BUG: kernel NULL pointer dereference, address: 0000000000000402
CPU: 14 PID: 306003 Comm: as Not tainted 5.9.0-1-amd64 #1 Debian 5.9.1-1
Hardware name: Lenovo ThinkSystem SR665/7D2VCTO1WW, BIOS D8E106Q-1.01 05/30/2020
RIP: 0010:fuse_readahead+0x152/0x470 [fuse]
Code: 41 8b 57 18 4c 8d 54 10 ff 4c 89 d6 48 8d 7c 24 10 e8 d2 e3 28 f9 48 85 c0 0f 84 fe 00 00 00 44 89 f2 49 89 04 d4 44 8d 72 01 <48> 8b 10 41 8b 4f 1c 48 c1 ea 10 83 e2 01 80 fa 01 19 d2 81 e2 01
RSP: 0018:ffffad99ceaebc50 EFLAGS: 00010246
RAX: 0000000000000402 RBX: 0000000000000001 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffff94c5af90bd98 RDI: ffffad99ceaebc60
RBP: ffff94ddc1749a00 R08: 0000000000000402 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000100 R12: ffff94de6c429ce0
R13: ffff94de6c4d3700 R14: 0000000000000001 R15: ffffad99ceaebd68
FS: 00007f228c5c7040(0000) GS:ffff94de8ed80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000402 CR3: 0000001dbd9b4000 CR4: 0000000000350ee0
Call Trace:
read_pages+0x83/0x270
page_cache_readahead_unbounded+0x197/0x230
generic_file_buffered_read+0x57a/0xa20
new_sync_read+0x112/0x1a0
vfs_read+0xf8/0x180
ksys_read+0x5f/0xe0
do_syscall_64+0x33/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 042124cc64c3 ("mm: add new readahead_control API")
Reported-by: David Sterba <dsterba@suse.com>
Reported-by: Wonhyuk Yang <vvghjk1234@gmail.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201103142852.8543-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20201103124349.16722-1-vvghjk1234@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/pagemap.h | 2 ++
1 file changed, 2 insertions(+)

--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -794,6 +794,8 @@ static inline unsigned int __readahead_b
xas_set(&xas, rac->_index);
rcu_read_lock();
xas_for_each(&xas, page, rac->_index + rac->_nr_pages - 1) {
+ if (xas_retry(&xas, page))
+ continue;
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageTail(page), page);
array[i++] = page;